{"id":152,"date":"2019-01-30T18:55:13","date_gmt":"2019-01-30T17:55:13","guid":{"rendered":"https:\/\/grupos.unican.es\/apye\/2019\/?page_id=152"},"modified":"2022-12-22T10:50:25","modified_gmt":"2022-12-22T09:50:25","slug":"investigacion","status":"publish","type":"page","link":"https:\/\/grupos.unican.es\/apye\/investigacion\/","title":{"rendered":"INVESTIGACI\u00d3N"},"content":{"rendered":"\n

PUBLICACIONES<\/h2>\n\n\n\n

2022<\/a> 2021<\/a> 2020<\/a> 2019<\/a> 2018<\/a> 2017<\/a> 2016<\/a> 2015<\/a> 2014<\/a> 2013<\/a> 2012<\/a> 2010<\/a> 2009<\/a> 2008 <\/a> 2007<\/a> 2006<\/a> 2005<\/a> 2004<\/a> 2003<\/a> 2002<\/a> 2001<\/a> 2000<\/a> 1999<\/a> 1998<\/a> 1997<\/a> 1996<\/a> 1995<\/a> 1994<\/a> 1993<\/a> 1992<\/a> 1991<\/a> 1990 <\/a> 1989<\/a> 1988<\/a> 1987<\/a> 1986<\/a> 1985<\/a> 1984<\/a> 1983<\/a> 1982<\/a> 1981<\/a> 1980<\/a><\/p>\n\n\n\n

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LIBROS<\/h2>\n\n\n\n
\"\"<\/figure>\n\n\n\n
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PATENTES<\/h2>\n\n\n\n

Vidrios de alta transmitancia, procedimiento de obtenci\u00f3n y aplicaciones fotovoltaicas<\/strong><\/p>\n\n\n\n

ES 2 381 948 B2<\/p>\n\n\n\n

INVENTORS: R. Valiente, F. Rodr\u00edguez, S. G\u00f3mez-Salces, J. A. Barreda-Ag\u00fceso.  Universidad de Cantabria<\/p>\n\n\n\n

High-transmittance glasses, synthesis method and photovoltaic applications<\/strong><\/p>\n\n\n\n

PCT\/ES2013\/000044R<\/p>\n\n\n\n

INVENTORS: R. Valiente, F. Rodr\u00edguez, S. G\u00f3mez-Salces, J. A. Barreda-Ag\u00fceso.  Universidad de Cantabria<\/p>\n\n\n\n

Microscopio para la caracterizaci\u00f3n espectrosc\u00f3pica de una muestra<\/strong><\/p>\n\n\n\n

P201300973 & PCT\/ES2014\/000049<\/p>\n\n\n\n

INVENTORS: J. A. Barreda-Ag\u00fceso, F. Rodr\u00edguez.  Universidad de Cantabria<\/p>\n\n\n\n

M\u00e9todo espectrosc\u00f3pico para la determinaci\u00f3n de prote\u00ednas en medios complejos<\/strong><\/p>\n\n\n\n

P201400165<\/p>\n\n\n\n

INVENTORS: V. Vali\u00f1o Llamazares, R. Valiente, M. F. San Rom\u00e1n San Emeterio, R. Ib\u00e1\u00f1ez Mendizabal, I. Ortiz Uribe.  Universidad de Cantabria<\/p>\n\n\n\n

Composici\u00f3n de nanofilamentos y su aplicaci\u00f3n t\u00f3pica en tumores de la piel<\/strong><\/p>\n\n\n\n

P201400254<\/p>\n\n\n\n

INVENTORS: M. L\u00f3pez-Fanarraga, R. Valiente, J. Gonz\u00e1lez. Universidad de Cantabria<\/p>\n\n\n\n

SENSOR LUMINISCENTE PARA LA MONITORIZACI\u00d3N DE RESIDUOS RADIACTIVOS Y USO DEL MISMO<\/strong><\/p>\n\n\n\n

(P202030404)<\/p>\n\n\n\n

INVENTORS: F. Aguado, R. Mart\u00edn-Rodr\u00edguez, A. C. Perdig\u00f3n, R. Valiente<\/p>\n\n\n\n

2022<\/strong><\/p>\n\n\n\n

Crystal-field mediated electronic transitions of EuS up to 35 GPa<\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

V. Monteseguro Padron, J.A. Barreda Argu\u0308eso, J. Ruiz Fuertes, A.D. Rosa, H.L. Meyerheim, T. Irifune, F. Rodriguez<\/p>\n\n\n\n

Source:<\/strong> Scientific Reports<\/p>\n\n\n\n

Volume:<\/strong> 12   P\u00e1ginas:<\/strong> 1217<\/p>\n\n\n\n

Abstract<\/strong>: An advanced experimental and theoretical model to explain the correlation between the electronic and local structure of Eu2+ in two different environments within a same compound, EuS, is presented. EuX<\/em> monochalcogenides (X<\/em>: O, S, Se, Te) exhibit anomalies in all their properties around 14 GPa with a semiconductor to metal transition. Although it is known that these changes are related to the 4\ud835\udc53<\/em>75\ud835\udc51<\/em>0 \u2192 4\ud835\udc53<\/em>65\ud835\udc51<\/em>1 electronic transition, no consistent model of the pressure-induced modifications of the electronic structure currently exists. We show, by optical and x-ray absorption spectroscopy, and by ab initio<\/em> calculations up to 35 GPa, that the pressure evolution of the crystal field plays a major role in triggering the observed electronic transitions from semiconductor to the half-metal and finally to the metallic state.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1038\/s41598-022-05321-9<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Correlation between Spectroscopic and Mechanical Properties of Gold Nanocrystals under Pressure<\/summary>
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Author(s):<\/strong> C. Martin Sanchez, A. S\u00e1nchez-Iglesias, P. Mulvaney, L. M. Liz-Marz\u00e1n, F. Rodriguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physical Chemistry C<\/p>\n\n\n\n

Volume:<\/strong> 12 6(4)  P\u00e1ginas:<\/strong> 1982-1990<\/p>\n\n\n\n

Abstract<\/strong>: The effects of nonhydrostatic pressure on the morphology and stability of gold nanorods (AuNRs) and nanospheres (AuNSs) in 4:1 methanol\u2013ethanol mixtures were studied by optical absorption spectroscopy and transmission electron microscopy at pressures of up to 23 and 30 GPa, respectively. Solvent solidification and associated nonhydrostatic stresses were found to have a negligible effect on the shape and size of AuNSs. On the contrary, while AuNRs maintained their initial morphology in the hydrostatic range, the uniaxial stress component induced under nonhydrostatic conditions had a shearing effect on the AuNRs, breaking them into smaller particles. Interestingly, colloidal stability was maintained in all cases, and the particles showed no sign of aggregation, despite the severe nonhydrostatic conditions to which both AuNR and AuNS colloids were subjected.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1021\/acs.jpcc.1c10767<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Graphene-encapsulated magnetic nanoparticles for safe and steady delivery of ferulic acid in diabetic mice<\/summary>
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Author(s):<\/strong> <\/p>\n\n\n\n

B. Zhong, A. Mateu-Rold\u00e1n, M. Lopez Fanarraga, W. Han, D. Mu\u00f1oz Guerra, J. Gonzalez, L. T. Weng, M. R. Ibarra, C. Marquina, K. L. Yeung<\/p>\n\n\n\n

Source:<\/strong> Chemical Engineering Journal<\/p>\n\n\n\n

Volume:<\/strong> 435  P\u00e1ginas:<\/strong> 134466<\/p>\n\n\n\n

Abstract<\/strong>: Iron nanoparticles<\/a> encapsulated within graphene shells (Fe@C) were examined for cellular internalization, subcellular behavior, biocompatibility, and influence on cell viability and proliferation. Studies on human lung (adenocarcinoma human alveolar basal epithelial) and skin (epidermoid carcinoma) cells indicate Fe@C is less toxic and more biocompatible than the magnetite<\/a> nanoparticles coated by an amorphous carbon (Fe3<\/sub>O4<\/sub>@C). Fe3<\/sub>O4<\/sub>@C exhibited more signs of degradation than Fe@C when exposed to murine macrophages (mouse monocyte-macrophages J774). Unlike Fe3<\/sub>O4<\/sub>@C, Fe@C has a high drug loading capacity (0.18 g\/g) for ferulic acid, an active pharmaceutical ingredient found in the traditional Chinese herb Angelica sinensis<\/em> and releases the drug at a constant dosing rate of 8.75 mg\/g\/day over 30 days. Ferulic acid released by Fe@C injected subcutaneously in diabetic BALB\/c mice is effective in lowering the blood glucose level.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Drug delivery, Diabetic mice, Carbon-coated magnetic nanoparticles, Graphene, Cytotoxicity<\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1016\/j.cej.2021.134466<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting \u03b2\u2010Cu2V2O7<\/summary>
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Author(s):<\/strong> <\/p>\n\n\n\n

R. Turnbull, J. Gonzalez-Platas, F. Rodr\u00edguez, A. Liang, C. Popescu, Z. He, D. Santamar\u00eda-P\u00e9rez, P. Rodr\u00edguez-Hern\u00e1ndez, A. Mu\u00f1oz, D. Errandonea<\/p>\n\n\n\n

Source:<\/strong> Inorganic Chemistry<\/p>\n\n\n\n

Volume:<\/strong> 61  P\u00e1ginas:<\/strong> 3697\u22123707<\/p>\n\n\n\n

Abstract<\/strong>: The understanding of the interplay between crystal structure and electronic structure in semiconductor materials is of great importance due to their potential technological applications. Pressure is an ideal external control parameter to tune the crystal structures of semiconductor materials in order to investigate their emergent piezo-electrical and optical properties. Accordingly, we investigate here the high-pressure behavior of the semiconducting antiferromagnetic material \u03b2-Cu2<\/sub>V2<\/sub>O7<\/sub>, finding it undergoes a pressure-induced phase transition to \u03b3-Cu2<\/sub>V2<\/sub>O7<\/sub> below 4000 atm. The pressure-induced structural and electronic evolutions are investigated by single-crystal X-ray diffraction, absorption spectroscopy and ab initio<\/em> density functional theory calculations. \u03b2-Cu2<\/sub>V2<\/sub>O7<\/sub> has previously been suggested as a promising photocatalyst for water splitting. Now, these new results suggest that \u03b2-Cu2<\/sub>V2<\/sub>O7<\/sub> could also be of interest with regards to barocaloric effects, due to the low phase -transition pressure, in particular because it is a multiferroic material. Moreover, the phase transition involves an electronic band gap decrease of approximately 0.2 eV (from 1.93 to 1.75 eV) and a large structural volume collapse of approximately 7%.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1021\/acs.inorgchem.1c03878<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Comment on \u201cMechanisms for Pressure-Induced Isostructural Phase Transitions in EuO\u201d<\/summary>
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Author(s):<\/strong> V. Monteseguro, J. Ruiz-Fuertes, J. A. Barreda-Argu\u0308eso, H. L. Meyerheim, A. D. Rosa, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Physical Review Letters<\/p>\n\n\n\n

Volume:<\/strong> 128  P\u00e1ginas:<\/strong> 099701<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1103\/PhysRevLett.128.099701<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure tuning of d\u2013d crystal-field electronic transitions and electronic band gap in Co(IO3)2<\/summary>
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Author(s):<\/strong> A. Liang, F. Rodr\u00edguez, P. Rodr\u00edguez-Hernandez, A. Mu\u00f1oz, R. Turnbull, and D. Errandonea<\/p>\n\n\n\n

Source:<\/strong> Physical Review B<\/p>\n\n\n\n

Volume:<\/strong> 105 (11)  P\u00e1ginas:<\/strong> 115204<\/p>\n\n\n\n

Abstract<\/strong>: High-pressure optical-absorption measurements performed on polycrystalline Co(IO3)2 samples were used to characterize the influence of pressure on the electronic d\u2013d transitions associated with Co2+ and the fundamental band gap of Co(IO3)2. The results shed light on the electron-lattice coupling and show that Co(IO3)2 exhibits an unusual behavior because the compression of Co\u2013O bond distances is not coupled to pressure-induced changes induced in the unit-cell volume. Experimental results on the internal d\u2013d transitions of Co2+ have been explained based on changes in the constituent CoO6 octahedral units using the semiempirical Tanabe-Sugano diagram. Our findings support that the high-spin ground state (T14) is very stable in Co(IO3)2. We have also determined the band-gap energy of Co(IO3)2 and its pressure dependence which is highly nonlinear. According to density-functional theory band-structure calculations, this nonlinearity occurs because the bottom of the conduction band is dominated by I-5p orbitals and the top of the valence band by Co-3d and O-2p orbitals, and because the Co\u2013O and I\u2013O bond lengths exhibit different pressure dependences.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.105.115204<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Non-resonant energy transfer from Eu3+ to Yb3+ in C-type and B-type (Eu1-xYbx)2O3 nanocrystals.<\/summary>
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Author(s):<\/strong> M. T. Candela, F. Aguado, A. Diego-Rucabado, J. A. Gonz\u00e1lez, and R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 921  P\u00e1ginas:<\/strong> 166043<\/p>\n\n\n\n

Abstract<\/strong>: The structural and spectroscopic properties of (Eu1-x<\/em><\/sub>Ybx<\/em><\/sub>)2<\/sub>O3<\/sub> nanocrystals<\/a> with cubic (C-type) and monoclinic (B-type) crystalline structures have been studied. NCs have been synthetized by the sol-gel Pechini method and characterized at room temperature by X-ray diffraction, transmission electron microscopy, diffuse reflectance, Raman spectroscopy<\/a> and photoluminescence<\/a> techniques. NIR emission from Yb3+<\/sup> ions has been observed in both C- and B-type NCs upon excitation of Eu3+<\/sup> ions at 532 nm, where Yb3+<\/sup> ions do not absorb photons. This fact reveals that an efficient non-resonant energy transfer process from Eu3+<\/sup> to Yb3+<\/sup> takes place, allowing to obtain simultaneous visible and NIR emissions under visible excitation. The decay curves of the 5<\/sup>D0<\/sub> \u2192 7<\/sup>F2<\/sub> Eu3+<\/sup> emission of C-type NCs corroborate this phenomenon since the Eu3+<\/sup> lifetime has been found to decrease as the Yb3+<\/sup> content increases. Finally, we discuss the use of the Eu3+<\/sup> luminescence as a structural probe to distinguish between different RE2<\/sub>O3<\/sub> polymorphs.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Rare Earth sesquioxides, Polymorphism, (Eu1-x<\/em><\/sub>Ybx<\/em><\/sub>)2<\/sub>O3<\/sub>, Nanocrystals, Photoluminescence, Non-resonant Energy transfer<\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1016\/j.jallcom.2022.166043<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Non-resonant energy transfer from Eu3+ to Yb3+ in C-type and B-type (Eu1-xYbx)2O3 nanocrystals.<\/summary>
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Author(s):<\/strong> M. T. Candela, F. Aguado, A. Diego-Rucabado, J. A. Gonz\u00e1lez, and R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 921  P\u00e1ginas:<\/strong> 166043<\/p>\n\n\n\n

Abstract<\/strong>: The structural and spectroscopic properties of (Eu1-x<\/em><\/sub>Ybx<\/em><\/sub>)2<\/sub>O3<\/sub> nanocrystals<\/a> with cubic (C-type) and monoclinic (B-type) crystalline structures have been studied. NCs have been synthetized by the sol-gel Pechini method and characterized at room temperature by X-ray diffraction, transmission electron microscopy, diffuse reflectance, Raman spectroscopy<\/a> and photoluminescence<\/a> techniques. NIR emission from Yb3+<\/sup> ions has been observed in both C- and B-type NCs upon excitation of Eu3+<\/sup> ions at 532 nm, where Yb3+<\/sup> ions do not absorb photons. This fact reveals that an efficient non-resonant energy transfer process from Eu3+<\/sup> to Yb3+<\/sup> takes place, allowing to obtain simultaneous visible and NIR emissions under visible excitation. The decay curves of the 5<\/sup>D0<\/sub> \u2192 7<\/sup>F2<\/sub> Eu3+<\/sup> emission of C-type NCs corroborate this phenomenon since the Eu3+<\/sup> lifetime has been found to decrease as the Yb3+<\/sup> content increases. Finally, we discuss the use of the Eu3+<\/sup> luminescence as a structural probe to distinguish between different RE2<\/sub>O3<\/sub> polymorphs.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Rare Earth sesquioxides, Polymorphism, (Eu1-x<\/em><\/sub>Ybx<\/em><\/sub>)2<\/sub>O3<\/sub>, Nanocrystals, Photoluminescence, Non-resonant Energy transfer<\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1016\/j.jallcom.2022.166043<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Exploring the local environment of the engineered nanoclay Mica-4 under hydrothermal conditions using Eu3+ as a luminescent probe<\/summary>
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Author(s):<\/strong> R. Mart\u00edn-Rodr\u00edguez, F. Aguado, M. D. Alba, R. Valiente, E. Pav\u00f3n, A. C. Perdig\u00f3n<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 921  P\u00e1ginas:<\/strong> 166086<\/p>\n\n\n\n

Abstract<\/strong>: High charge mica Na4<\/sub>Al4<\/sub>Si4<\/sub>Mg6<\/sub>O20<\/sub>F4<\/sub>, Mica-4, is a promising candidate as a filling material to immobilize high-level radioactive waste in deep geological repositories due to its extraordinary adsorption capacity. In contrast to traditional clay materials, the structural composition of this mica, with a high content of aluminum in the tetrahedral sheet, enhances its chemical reactivity, favoring the formation of new crystalline phases under mild hydrothermal conditions, and thus providing a definitive isolation of the radionuclides in the engineered barrier. Moreover, this synthetic clay has some features that allow its use as an optical sensor<\/a> by doping with luminescent rare earth cations such as Eu3+<\/sup>. In this paper we discuss the local structure of the nanoclay<\/a> Mica-4 using Eu3+<\/sup> as a local probe to track the physical and chemical modifications under hydrothermal conditions. For that purpose, a set of hydrothermal experiments has been carried out heating Mica-4 and an aqueous Eu(NO3<\/sub>)3<\/sub> solution in a stainless steel reactor at different temperatures and times. Optical properties of the as-treated samples were characterized by spectroscopic measurements. The fine peak structure of emission and the relative intensity of different Eu3+<\/sup> transitions as well as the luminescence lifetime have been correlated with the structure and composition of this nanoclay, and the interaction mechanisms between the lanthanide<\/a> ions and the clay mineral at different temperatures and times. Special attention has been paid to understanding the role of the aluminum content, which may act as either an aggregating or dispersing agent, in the optical features and reactivity of the system.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Deep Geological Repository, Adsorption, Luminescence, Optical sensor, Radionuclide, High-charge mica<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1016\/j.jallcom.2022.166086<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical spectroscopy of the Sr4Al14O25: Mn4+, Cr3+ phosphor: pressure and temperature dependences.<\/summary>
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Author(s):<\/strong> E. Jara, R. Valiente, J. Gonz\u00e1lez, J. I. Espeso, N. Khaidukov, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Materials Chemistry C<\/p>\n\n\n\n

Volume:<\/strong> 10 (16)  P\u00e1ginas:<\/strong> 6380-6391<\/p>\n\n\n\n

Abstract<\/strong>: We present a spectroscopic study of the doubly Mn4+<\/sup><\/small> and Cr3+<\/sup><\/small>-doped Sr4<\/sub><\/small>Al14<\/sub><\/small>O25<\/sub><\/small>, synthesised via<\/em> solid state reaction, as a function of pressure and temperature to check its potential as a red emitting phosphor. The strong crystal field acting on Cr3+<\/sup><\/small> yields a ruby-like narrow R-line emission that is used as an intrinsic temperature sensor and, in comparison to ruby, provides a fair estimate of the bulk modulus K<\/em> = 172 GPa for Sr4<\/sub><\/small>Al14<\/sub><\/small>O25<\/sub><\/small>. The photoluminescence (PL) and associated excitation spectra of Sr4<\/sub><\/small>Al14<\/sub><\/small>O25<\/sub><\/small>:Mn4+<\/sup><\/small>,Cr3+<\/sup><\/small> unravel a strong-field 3d3<\/sup><\/small> configuration with R<\/em>1<\/sub><\/small> and R<\/em>2<\/sub><\/small> emission lines largely separated by 10.7 meV, which characterizes the non-centrosymmetric distorted Al4 site in the Sr4<\/sub><\/small>Al14<\/sub><\/small>O25<\/sub><\/small> structure. Eighteen Raman modes have been detected at ambient pressure. They correspond to the stretching modes of the Al\u2013O bonds and show frequency shifts with pressure consistent with Gr\u00fcneisen parameters (\u03b3<\/em> = 0.65), similar to those measured for other aluminates. The variations of PL intensity and lifetime with temperature exhibit a similar concomitant behaviour indicating an efficient pumping to the 4<\/sup><\/small>T<\/em>2<\/sub><\/small> level and hence down to the 2<\/sup><\/small>E emitting level in both Mn4+<\/sup><\/small> and Cr3+<\/sup><\/small> ions at low and moderate temperatures. Multiphonon non-radiative processes yield a quenching temperature of 400 K for Mn4+<\/sup><\/small> with an effective activation energy of 0.57 eV. Unexpectedly, this energy decreases with pressure enhancing the non-radiative processes and thus PL intensity reduction. A thoroughly coordinate configurational energy diagram is presented for explaining the main spectroscopic features and excited-state dynamics.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D2TC00485B<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Shiga toxin-B targeted gold nanorods for local photothermal treatment in oral cancer clinical simples.<\/summary>
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Author(s):<\/strong> E. Navarro-Palomares, L. Garc\u00eda-Hevia, J. Gal\u00e1n-Vidal, A. Gandarillas, F. Garc\u00eda-Reija, A. S\u00e1nchez-Iglesias, L. M. Liz- Marzan, R. Valiente and M. L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> International J. Nanomedicine<\/p>\n\n\n\n

Volume:<\/strong>   P\u00e1ginas:<\/strong> Aceptado<\/p>\n\n\n\n

Abstract<\/strong>: A great challenge in nanomedicine, and more specifically in theranostics, is to improve the specificity, selectivity, and targeting of nanomaterials towards target tissues or cells. The topical use of nanomedicines as adjuvants to systemic chemotherapy can significantly improve the survival of patients affected by localized carcinomas, reducing the side effects of traditional drugs and preventing local recurrences.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> unctionalized nanomaterial; globotriaosylceramide; nanoparticle targeting; natural ligand; squamous carcinoma.<\/p>\n\n\n\n

DOI:<\/strong> 10.2147\/IJN.S381628<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Behavior of Au Nanoparticles under Pressure Observed by In Situ Small-Angle X\u2010ray Scattering<\/summary>
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Author(s):<\/strong> C. Mart\u00edn-S\u00e1nchez, A. S\u00e1nchez-Iglesias, J.A. Barreda-Argu\u0308eso, A Polian, L. M. Liz-Marz\u00e1n, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> ACS Nano<\/p>\n\n\n\n

Volume:<\/strong>   P\u00e1ginas:<\/strong> Aceptado<\/p>\n\n\n\n

Abstract<\/strong>: The mechanical properties and stability of metal nanoparticle colloids under high-pressure conditions are investigated by means of optical extinction spectroscopy and small-angle X-ray scattering (SAXS), for colloidal dispersions of gold nanorods and gold nanospheres. SAXS allows us to follow in situ the structural evolution of the nanoparticles induced by pressure, regarding both nanoparticle size and shape (form factor) and their aggregation through the interparticle correlation function S<\/em>(q<\/em>) (structure factor). The observed behavior changes under hydrostatic and nonhydrostatic conditions are discussed in terms of liquid solidification processes yielding nanoparticle aggregation. We show that pressure-induced diffusion and aggregation of gold nanorods take place after solidification of the solvent. The effect of nanoparticle shape on the aggregation process is additionally discussed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> gold nanoparticles, high-pressure, small-angle X-ray scattering, aggregation, pressure-induced diffusion<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1021\/acsnano.2c10643<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

2021<\/strong><\/p>\n\n\n\n

Pressure dependence of the crystal-field spectrum of KNiF3 : Single and double excitations<\/summary>
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Author(s):<\/strong> J.A. Barreda-Argu\u0308eso, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Physical Review B<\/p>\n\n\n\n

Volume:<\/strong> 103   P\u00e1ginas:<\/strong> 085115<\/p>\n\n\n\n

Abstract<\/strong>: This work investigates the Ni-F distance dependence of the crystal-field (CF) transitions of Ni2+ in KNiF3 by high-pressure spectroscopy. All peaks shift to higher energy with pressure according to trends foreseen by the Tanabe-Sugano diagram. At ambient conditions, we obtain Racah and CF splitting parameters of B=0.118eV, 10Dq=0.908eV; C\/B=4.4 (10Dq\/B=7.7). B and 10Dq vary with pressure as \u2202B\u2202P=\u20130.11meVGPa\u20131 and \u220210Dq\u2202P=24meVGPa\u20131. Similar to KCoF3, the slight decrease of B with pressure reflects the strong ionic character of the Ni-F bond and its high stability against compression. We have correlated the measured pressure dependence of 10Dq with the Ni-F bond distance, showing that it follows a potential law as 10Dq=CR\u2013n with an exponent n=6.6\u00b10.5, thus providing experimental data for checking the suitability of theoretical models aiming to explain the slight deviations of observed R dependencies of 10Dq from the CF theory (n=5). We have applied the experimental 10Dq(R) relationship to determine the real Ni-F bond distances in fluoroperovskites ABF3:Ni2+ from the spectroscopically measured 10Dq as an alternative method for determining bond distances, RNi\u2212F, in impurity systems. We show that the so-obtained RNi\u2212F deviates from the bond distance of the host site, RB\u2212F, proportionally to the difference RB\u2212F\u2212R0, with R0 being the sum of ionic radii RF\u2212+RNi2+. The behavior is compared to that found for Mn2+ along the fluoroperovskite series ABF3:Mn2+. Finally, weak UV peaks observed below the charge-transfer band gap (Eg\u226410eV) in the absorption spectrum, the assignment of which still remains controversial, have been assigned to single and double excitation transitions. The assignment was unveiled on the basis of their energy and pressure shift.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1103\/PhysRevB.103.085115<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Local structure in Ga1-xInxSe alloys<\/summary>
\n

Author(s):<\/strong> J. Pellicer-Porres, A. Segura, Ch. Ferrer-Roca, J. A. Gonzalez, V. Mu\u00f1oz-San jose<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 852   P\u00e1ginas:<\/strong> 156365<\/p>\n\n\n\n

Abstract<\/strong>: In this work we study the local structure of layered alloys by means of X-ray Absorption. We complement our research with a Raman study. The available alloys have compositions close to the host binaries. The dependence of XANES (X-ray Near Edge Structure) features with synchrotron polarization clearly establishes the substitutional character of the alloying cations. Interstitial atoms, if present, remain under the detection limit of the technique. EXAFS (Extended X-ray Absorption Fine Structure) demonstrates the existence of bonds in the alloys. The cation-anion bond-lengths in the alloys remain similar to that of the pure compounds. There is no significant increase of the static disorder. The basic features of Raman spectra are those of the pure compounds, with the Raman peaks shifting continuously as the impurity cation is introduced. New features associated to defects are discussed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

Layered semiconductor, X-ray absorption, XANES, EXAFS, Raman, Alloy<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1103\/PhysRevB.103.085115<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Solid Lipid Particles for Lung Metastasis Treatment<\/summary>
\n

Author(s):<\/strong> L. Valdivia, L. Garc\u00eda-Hevia, M. Ba\u00f1obre-L\u00f3pez, J. Gallo, R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Pharmaceutics<\/p>\n\n\n\n

Volume:<\/strong> 13   P\u00e1ginas:<\/strong> 93<\/p>\n\n\n\n

Abstract<\/strong>: Solid lipid particles (SLPs) can sustainably encapsulate and release therapeutic agents over long periods, modifying their biodistribution, toxicity, and side effects. To date, no studies have been reported using SLPs loaded with doxorubicin chemotherapy for the treatment of metastatic cancer. This study characterizes the effect of doxorubicin-loaded carnauba wax particles in the treatment of lung metastatic malignant melanoma in vivo. Compared with the free drug, intravenously administrated doxorubicin-loaded SLPs significantly reduce the number of pulmonary metastatic foci in mice. In vitro kinetic studies show two distinctive drug release profiles. A first chemotherapy burst-release wave occurs during the first 5 h, which accounts for approximately 30% of the entrapped drug rapidly providing therapeutic concentrations. The second wave occurs after the arrival of the particles to the final destination in the lung. This release is sustained for long periods (>40 days), providing constant levels of chemotherapy in situ that trigger the inhibition of metastatic growth. Our findings suggest that the use of chemotherapy with loaded SLPs could substantially improve the effectiveness of the drug locally, reducing side effects while improving overall survival.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> cancer; doxorubicin; drug delivery; melanoma; nanomedicine.<\/p>\n\n\n\n

DOI:<\/strong> 10.3390\/pharmaceutics13010093<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photocatalytic activity of undoped and Mn-and Co-doped TiO2 nanocrystals incorporated in enamel coatings on stainless steel<\/summary>
\n

Author(s):<\/strong> A Diego-Rucabado, M.T. Candela, F. Aguado, J. Gonz\u00e1lez, E. G\u00f3mez, R. Valiente, I. Cano, R. Mart\u00edn-Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Reaction Chemistry & Engineering<\/p>\n\n\n\n

Volume:<\/strong> 6   P\u00e1ginas:<\/strong> 2376-2390<\/p>\n\n\n\n

Abstract<\/strong>: A series of undoped and transition-metal (TM)-doped TiO2<\/sub><\/small> nanocrystals (NCs) were synthesized and calcined at different temperatures, and fully characterized. Such NCs were employed as catalysts for the photodegradation of methylene blue, which enabled us to study the influence of both NC size and anatase\/brookite\/rutile phase ratio on the photocatalytic activity, as well as the effect of different TM dopants, namely Mn and Co. Then, the NCs were used as active additives for the fabrication of a new photocatalytic system composed of an enamel incorporating these NCs supported onto a stainless-steel sheet. NCs both in powder form and incorporated in enamels deposited on steel were characterized by transmission electron microscopy, X-ray diffraction, and reflectance and Raman spectroscopy. We demonstrate how the calcination of TiO2<\/sub><\/small> NCs induces both a growth in the anatase ratio and formation of the rutile form, which leads to a photocatalytic activity increase. Similarly, doping with Mn and Co gives rise to an enhancement of the catalytic performance attributed to a displacement of the energy bandgap. The obtained material combines the resistance of steel and the photocatalytic activity of TiO2<\/sub><\/small> deposited on enamel, which also operates as a corrosion protection layer for the former. The resulting smart photocatalytic surface presents many applications such as a self-cleaning coating and potential use for NOx photodegradation.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D1RE00293G<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-Driven Metallization in Hafnium Diselenide<\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

A. Andrada-Chac\u00f3n, \u00c1. Morales-Garc\u00eda, M. A. Salvad\u00f3, P. Pertierra, R. Franco, G. Garbarino, M. Taravillo, J. A. Barreda-Argu\u0308eso, J. Gonz\u00e1lez, Valent\u00edn Garc\u00eda Baonza, J. Manuel Recio, Javier S\u00e1nchez-Ben\u00edtez<\/p>\n\n\n\n

Source:<\/strong> Inorg. Chem.<\/p>\n\n\n\n

Volume:<\/strong> 60, 3   P\u00e1ginas:<\/strong> 1746-1754<\/p>\n\n\n\n

Abstract<\/strong>: The quest for new transition metal dichalcogenides (TMDs) with outstanding electronic properties operating under ambient conditions draws us to investigate the 1T-HfSe2<\/sub> polytype under hydrostatic pressure. Diamond anvil cell (DAC) devices coupled to in situ<\/em> synchrotron X-ray, Raman, and optical (VIS\u2013NIR) absorption experiments along with density functional theory (DFT)-based calculations prove that (i) bulk 1T-HfSe2<\/sub> exhibits strong structural and vibrational anisotropies, being the interlayer direction especially sensitive to pressure changes, (ii) the indirect gap of 1T-HfSe2<\/sub> tends to vanish by a \u22120.1 eV\/GPa pressure rate, slightly faster than MoS2<\/sub> or WS2<\/sub>, (iii) the onset of the metallic behavior appears at P<\/em>met<\/sub> \u223c10 GPa, which is to date the lowest pressure among common TMDs, and finally, (iv) the electronic transition is explained by the bulk modulus B<\/em>0<\/sub>–P<\/em>met<\/sub> correlation, along with the pressure coefficient of the band gap, in terms of the electronic overlap between chalcogenide p-type and metal d-type orbitals. Overall, our findings identify 1T-HfSe2<\/sub> as a new efficient TMD material with potential multipurpose technological applications.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1021\/acs.inorgchem.0c03223<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Revealing a masked Verwey transition in nanoparticles of coexisting Fe-oxide phases<\/summary>
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Author(s):<\/strong> <\/p>\n\n\n\n

D. Gonzalez-Alonso, J. Gonz\u00e1lez, H. Gavilan, J. Fock, L. Zeng, K. Witte, P. Bender, L. Fernandez-Barquin, C. Johansson<\/p>\n\n\n\n

Source:<\/strong> RSC Advances<\/p>\n\n\n\n

Volume:<\/strong> 11   P\u00e1ginas:<\/strong> 390<\/p>\n\n\n\n

Abstract<\/strong>: The attractive electronic and magnetic properties together with their biocompatibility make iron-oxide nanoparticles appear as functional materials. In Fe-oxide nanoparticle (IONP) ensembles, it is crucial to enhance their performance thanks to controlled size, shape, and stoichiometry ensembles. In light of this, we conduct a comprehensive investigation in an ensemble of ca.<\/em> 28 nm cuboid-shaped IONPs in which all the analyses concur with the coexistence of magnetite\/maghemite phases in their cores. Here, we are disclosing the Verwey transition by temperature dependent (4\u2013210 K) Raman spectroscopy.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D0RA09226F<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Modification of the spectroscopic properties of Tb2O3 phosphor under the high-pressure phase transitions sequence<\/summary>
\n

Author(s):<\/strong> M.T. Candela, F. Aguado, J.A. Gonzalez, R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 859   P\u00e1ginas:<\/strong> 157899<\/p>\n\n\n\n

Abstract<\/strong>: The attractive electronic and magnetic properties together with their biocompatibility make iron-oxide nanoparticles appear as functional materials. In Fe-oxide nanoparticle (IONP) ensembles, it is crucial to enhance their performance thanks to controlled size, shape, and stoichiometry ensembles. In light of this, we conduct a comprehensive investigation in an ensemble of ca.<\/em> 28 nm cuboid-shaped IONPs in which all the analyses concur with the coexistence of magnetite\/maghemite phases in their cores. Here, we are disclosing the Verwey transition by temperature dependent (4\u2013210 K) Raman spectroscopy.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Phosphors, High-pressure, Phase transitions, Luminescence, Inelastic light scattering<\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1016\/j.jallcom.2020.157899<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopy of the frustrated quantum antiferromagnet Cs2<\/sub>CuCl4<\/sub><\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

A.O. Fumega, D. Wong, C. Schulz, F. Rodr\u00edguez, S. Blanco-Canosa<\/p>\n\n\n\n

Source:<\/strong> Journal of Physics: Condensed Matter<\/p>\n\n\n\n

Volume:<\/strong> 33(49)   P\u00e1ginas:<\/strong> 495603<\/p>\n\n\n\n

Abstract<\/strong>: We investigate the electronic structure of Cs2<\/sub>CuCl4<\/sub>, a material discussed in the framework of a frustrated quantum antiferromagnet, by means of resonant inelastic x-ray scattering (RIXS) and density functional theory (DFT). From the non-dispersive highly localized dd<\/em> excitations, we resolve the crystal field splitting of the Cu2+<\/sup> ions in a strongly distorted tetrahedral coordination. This allows us to model the RIXS spectrum within the crystal field theory (CFT), assign the dd<\/em> orbital excitations and retrieve experimentally the values of the crystal field splitting parameters D<\/em>q<\/em><\/sub>, D<\/em>s<\/em><\/sub> and D<\/em>\u03c4<\/em><\/sub>. The electronic structure obtained ab-initio<\/em> agrees with the RIXS spectrum and modelled by CFT, highlighting the potential of combined spectroscopic, cluster and DFT calculations to determine the electronic ground state of complex materials.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/1361-648X\/ac2648<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Nd3+-Doped Lanthanum Oxychloride Nanocrystals as Nanothermometers<\/summary>
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Author(s):<\/strong> C. Renero, A. Herrero, D. Jimenez, M. Mart\u00ednez-Fl\u00f3rez, R. Valiente, M. Mychinko, S. Bals, L. M. Liz-Marz\u00e1n<\/p>\n\n\n\n

<\/p>\n\n\n\n

Source:<\/strong> The Journal of Physical Chemistry C<\/p>\n\n\n\n

Volume:<\/strong> 125   P\u00e1ginas:<\/strong> 19887-19896<\/p>\n\n\n\n

Abstract<\/strong>: The development of optical nanothermometers operating in the near-infrared (NIR) is of high relevance toward temperature measurements in biological systems. We propose herein the use of Nd3+<\/sup>-doped lanthanum oxychloride nanocrystals as an efficient system with intense photoluminescence under NIR irradiation in the first biological transparency window and emission in the second biological window with excellent emission stability over time under 808 nm excitation, regardless of Nd3+<\/sup> concentration, which can be considered as a particular strength of our system. Additionally, surface passivation through overgrowth of an inert LaOCl shell around optically active LaOCl\/Nd3+<\/sup> cores was found to further enhance the photoluminescence intensity and also the lifetime of the 1066 nm, 4<\/sup>F3\/2<\/sub> to 4<\/sup>I11\/2<\/sub> transition, without affecting its (ratiometric) sensitivity toward temperature changes. As required for biological applications, we show that the obtained (initially hydrophobic) nanocrystals can be readily transferred into aqueous solvents with high, long-term stability, through either ligand exchange or encapsulation with an amphiphilic polymer.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1021\/acs.jpcc.1c05828<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Targeting Nanomaterials to Head and Neck Cancer Cells Using A Fragment of the Shiga Toxin as a Potent Natural Ligand<\/summary>
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Author(s):<\/strong> E. Navarro, L. Garc\u00eda-Hevia, E. Pad\u00edn-Gonz\u00e1lez, M. Ba\u00f1obre-L\u00f3pez, J.C. Villegas, R. Valiente, M.L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> Cancers<\/p>\n\n\n\n

Volume:<\/strong> 13   P\u00e1ginas:<\/strong> 4920 (1-14)<\/p>\n\n\n\n

Abstract<\/strong>: Head and Neck Cancer (HNC) is the seventh most common cancer worldwide with a 5-year survival from diagnosis of 50%. Currently, HNC is diagnosed by a physical examination followed by an histological biopsy, with surgery being the primary treatment. Here, we propose the use of targeted nanotechnology in support of existing diagnostic and therapeutic tools to prevent recurrences of tumors with poorly defined or surgically inaccessible margins. We have designed an innocuous ligand-protein, based on the receptor-binding domain of the Shiga toxin (ShTxB), that specifically drives nanoparticles to HNC cells bearing the globotriaosylceramide receptor on their surfaces. Microscopy images show how, upon binding to the receptor, the ShTxB-coated nanoparticles cause the clustering of the globotriaosylceramide receptors, the protrusion of filopodia, and rippling of the membrane, ultimately allowing the penetration of the ShTxB nanoparticles directly into the cell cytoplasm, thus triggering a biomimetic cellular response indistinguishable from that triggered by the full-length Shiga toxin. This functionalization strategy is a clear example of how some toxin fragments can be used as natural biosensors for the detection of some localized cancers and to target nanomedicines to HNC lesions.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> oral cancer; nanotechnology; toxin; recombinant ligand-protein<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.3390\/cancers13194920<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Adsorptive Capture of Ionic and Non-Ionic Pollutants Using a Versatile Hybrid Amphiphilic-Nanomica<\/summary>
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Author(s):<\/strong> F. Aguado, R. Mart\u00edn-Rodr\u00edguez, C. Pesquera, R. Valiente, A. C. Perdig\u00f3n<\/p>\n\n\n\n

Source:<\/strong> Nanomaterials<\/p>\n\n\n\n

Volume:<\/strong> 11   P\u00e1ginas:<\/strong> 3167, 1-13<\/p>\n\n\n\n

Abstract<\/strong>: A versatile, functional nanomaterial for the removal of ionic and non-ionic pollutants is presented in this work. For that purpose, the high charge mica Na-4-Mica was exchanged with the cationic surfactant (C16<\/sub>H33<\/sub>NH(CH3<\/sub>)2<\/sub>)+<\/sup>. The intercalation of the tertiary amine in the swellable nano-clay provides the optimal hydrophilic\/hydrophobic nature in the bidimensional galleries of the nanomaterial responsible for the dual functionality. The organo-mica, made by functionalization with C16<\/sub>H33<\/sub>NH3<\/sub>+<\/sup>, was also synthesized for comparison purposes. Both samples were characterized by X-ray diffraction techniques and transmission electron microscopy. Then, the samples were exposed to a saturated atmosphere of cyclohexylamine for two days, and the adsorption capacity was evaluated by thermogravimetric measurements. Eu3+<\/sup> cations served as a proof of concept for the adsorption of ionic pollutants in an aqueous solution. Optical measurements were used to identify the adsorption mechanism of Eu3+<\/sup> cations, since Eu3+<\/sup> emissions, including the relative intensity of different f-f<\/em> transitions and the luminescence lifetime, can be used as an ideal spectroscopic probe to characterize the local environment. Finally, the stability of the amphiphilic hybrid nanomaterial after the adsorption was also tested.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Eu3+ luminescence; adsorption; calorimetry; decontamination; high charge mica; ionic pollutants; non-ionic pollutants.<\/p>\n\n\n\n

DOI:<\/strong> 10.3390\/nano11123167.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Structural, vibrational and electronic properties of \u03b1-Ga2S3 under compression<\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

S. Gallego-Parra, R. Vilaplana, O. Gomis, E. Lora Da Silva, A. Otero-De-La-Roza, P. Rodr\u00edguez-Hern\u00e1ndez, A. Mu\u00f1oz, J. A. Gonzalez, J. A. Sans, V. P. Cuenca-Gotor, J. Ib\u00e1\u00f1ez, C. Popescu, F. J. Manj\u00f3n<\/p>\n\n\n\n

Source:<\/strong> Physical Chemistry Chemical Physics<\/p>\n\n\n\n

Volume:<\/strong> 12   P\u00e1ginas:<\/strong> 6841-6862<\/p>\n\n\n\n

Abstract<\/strong>: We report a joint experimental and theoretical study of the low-pressure phase of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small> under compression. Theoretical ab initio<\/em> calculations have been compared to X-ray diffraction and Raman scattering measurements under high pressure carried out up to 17.5 and 16.1 GPa, respectively. In addition, we report Raman scattering measurements of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small> at high temperature that have allowed us to study its anharmonic properties. To understand better the compression of this compound, we have evaluated the topological properties of the electron density, the electron localization function, and the electronic properties as a function of pressure. As a result, we shed light on the role of the Ga\u2013S bonds, the van der Waals interactions inside the channels of the crystalline structure, and the single and double lone electron pairs of the sulphur atoms in the anisotropic compression of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small>. We found that the structural channels are responsible for the anisotropic properties of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small> and the A\u2032(6) phonon, known as the breathing mode and associated with these channels, exhibits the highest anharmonic behaviour. Finally, we report calculations of the electronic band structure of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small> at different pressures and find a nonlinear pressure behaviour of the direct band gap and a pressure-induced direct-to-indirect band gap crossover that is similar to the behaviour previously reported in other ordered-vacancy compounds, including \u03b2-Ga2<\/sub><\/small>Se3<\/sub><\/small>. The importance of the single and, more specially, the double lone electron pairs of sulphur in the pressure dependence of the topmost valence band of \u03b1\u2032-Ga2<\/sub><\/small>S3<\/sub><\/small> is stressed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1039\/D0CP06417C<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Free-labeled nanoclay intracellular uptake tracking by confocal Raman imaging<\/summary>
\n

Author(s):<\/strong> N. Iturrioz, R. Martin-Rodriguez, C. Renero-Lecuna, F. Aguado, L. Gonzalez-Legarreta J. A. Gonzalez, et al.<\/p>\n\n\n\n

Source:<\/strong> Applied Surface Science<\/p>\n\n\n\n

Volume:<\/strong> 537   P\u00e1ginas:<\/strong> 147870<\/p>\n\n\n\n

Abstract<\/strong>: Laponite is a nanoplatform that has been successfully used as a new biomaterial for drug delivery, tissue engineering and bioimaging at the nanoscale. In general, a deep knowledge of the mechanism interaction of the nanomaterial with biological components in a physiological environment is highly desirable for properly characterizing its therapeutic efficacy and toxicology. Up to know, the use of fluorescent dyes labelling both, the nanomaterial and cell components, has been a requirement to characterize the cell uptake and to visualize the entrance of the nanomaterial into the cytosol and the cell nucleus. The used of fluorophores usually perturb the physiological medium and can interfere in the nanomaterial cell interaction. A new Raman imaging methodology to track the uptake and internalization of Laponite nanoparticles into J774 macrophages line cells is presented in this work. The combination of Raman spectroscopy and confocal microscopy provides direct information about the localization of the nanoparticle into the cell, through its unique vibrational fingerprint without labelling or adding dyes, and taking advantage of the fact that Laponite and biological molecules bands can be clearly differentiated.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Laponite, Nanomaterial, Nanocarrier, Raman imaging technique, Nanoclay<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1016\/j.apsusc.2020.147870<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Stokes and upconverted luminescence in Er3+\/Yb3+-doped Y3Ga5O12nano-garnets<\/summary>
\n

Author(s):<\/strong> V. Monteseguro, V. Venkatramu, U.R. Rodr\u00edguez-Mendoza, V. Lav\u00edn<\/p>\n\n\n\n

Source:<\/strong> Dalton Transactions<\/p>\n\n\n\n

Volume:<\/strong> 50(27)   P\u00e1ginas:<\/strong> 9512-9518<\/p>\n\n\n\n

Abstract<\/strong>: The green, red, near-infrared and near-infrared-to-visible upconverted luminescence properties of Er3+<\/sup><\/small>\/Yb3+<\/sup><\/small> codoped Y3<\/sub><\/small>Ga5<\/sub><\/small>O12<\/sub><\/small> nanocrystalline powders have been studied using laser spectroscopy. A diffuse reflectance and luminescence spectra confirm that Er3+<\/sup><\/small> and Yb3+<\/sup><\/small> ions occupy the Y3+<\/sup><\/small> sites of the single-phase cubic nano-garnet. Very bright green and red luminescence of the Er3+<\/sup><\/small> ions are detected by the naked eyes, even for a laser power as low as 15 mW, when the Yb3+<\/sup><\/small> ions are excited at 970 nm. The red upconverted emission is more intense than that under direct excitation of the Er3+<\/sup><\/small> ions. The power dependence and the dynamics of the near-infrared-to-green and near-infrared-to-red upconverted emissions show the existence of different two-photon energy transfer upconversion processes. The results here presented indicate that Er3+<\/sup><\/small>\/Yb3+<\/sup><\/small> codoped Y3<\/sub><\/small>Ga5<\/sub><\/small>O12<\/sub><\/small> can be a good candidate as an optical nanoheater and nanothermometer in biomedicine applications in the first biological window.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D1DT00976A<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Unveiling the role of the lone electron pair in sesquioxides at high pressure: compressibility of \u03b2-Sb2O3.<\/summary>
\n

Author(s):<\/strong> V. Monteseguro, V. Venkatramu, U.R. Rodr\u00edguez-Mendoza, V. Lav\u00edn<\/p>\n\n\n\n

Source:<\/strong> Dalton Transactions<\/p>\n\n\n\n

Volume:<\/strong> 50(16)   P\u00e1ginas:<\/strong> 5493-5505<\/p>\n\n\n\n

Abstract<\/strong>: The structural, vibrational and electronic properties of the compressed \u03b2-Sb2<\/sub><\/small>O3<\/sub><\/small> polymorph, a.k.a. mineral valentinite, have been investigated in a joint experimental and theoretical study up to 23 GPa. The compressibility of the lattice parameters, unit-cell volume and polyhedral unit volume as well as the behaviour of its Raman- and IR-active modes under compression have been interpreted on the basis of ab initio<\/em> theoretical simulations. Valentinite shows an unusual compressibility up to 15 GPa with four different pressure ranges, whose critical pressures are 2, 4, and 10 GPa. The pressure dependence of the main structural units, the lack of soft phonons, and the electronic density charge topology address the changes at those critical pressures to isostructural phase transitions of degree higher than 2. In particular, the transitions at 2 and 4 GPa can be ascribed to the changes in the interaction between the stereochemically-active lone electron pairs of Sb atoms under compression. The changes observed above 10 GPa, characterized by a general softening of several Raman- and IR-active modes, point to a structural instability prior to the 1st-order transition occurring above 15 GPa. Above this pressure, a tentative new high-pressure phase (s.g. Pcc<\/em>2) has been assigned by single-crystal and powder X-ray diffraction measurements.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D1DT00976A<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Understanding the Efficiency of Mn4+ Phosphors: Study of the Spinel Mg2Ti1\u2013xMnxO4<\/summary>
\n

Author(s):<\/strong> E. Jara, R. Valiente, M. Bettinelli, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> The Journal of Physical Chemistry C<\/p>\n\n\n\n

Volume:<\/strong> 125   P\u00e1ginas:<\/strong> 27118\u201327129<\/p>\n\n\n\n

Abstract<\/strong>: We present a spectroscopic study of Mn-doped Mg2TiO4 as a function of pressure and temperature to check its viability as a red-emitting phosphor. The synthesis following a solid-state reaction route yields not only the formation of Mn4+ but also small traces of Mn3+. Although we show that Mn4+ photoluminescence is not appreciably affected by the presence of Mn3+, its local structure at the substituted Ti4+ host site causes a reduction of the Mn4+ pumping efficiency yielding a drastic quantum-yield reduction at room temperature. By combining Raman and time-resolved emission and excitation spectroscopies, we propose a model for explaining the puzzling nonradiative and inefficient pumping processes attained in this material. In addition, we unveil a structural phase transition above 14 GPa that worsens their photoluminescence capabilities. The decrease of emission intensity and lifetime with increasing temperature following different thermally activated de-excitation pathways is mostly related to relatively small activation energies and the electric\u2212dipole transition mechanism associated with coupling to odd-parity vibrational modes. A thorough model based on the configurational energy level diagram to the A1g normal mode fairly accounts for the observed excitation and emission\ue0d5the quantum yield\ue0d5of this material.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> <\/a>10.1021\/acs.jpcc.1c08006<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

On the Stiffness of Gold at the Nanoscale<\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

C. Mart\u00edn-S\u00e1nchez, A. S\u00e1nchez-Iglesias, J.A. Barreda-Argu\u0308eso, A Polian, J.P. Iti\u00e9, J. P\u00e9rez, P. Mulvaney, L. M. Liz-Marz\u00e1n, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> ACS Nano<\/p>\n\n\n\n

Volume:<\/strong> 15   P\u00e1ginas:<\/strong> 19128\u201319137<\/p>\n\n\n\n

Abstract<\/strong>: The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-ray scattering. We demonstrate that nonhydrostatic effects due to solvent solidification had a negligible influence on the stability of the nanoparticles. Conversely, nonhydrostatic effects produced axial stresses on the nanoparticle up to a factor 10\u00d7 higher than those on the bulk metal. Working under hydrostatic conditions (liquid solution), we determined the equation of state of individual nanoparticles. From the values of the lattice parameter and bulk modulus, we found that gold nanoparticles are slightly denser (0.3%) and stiffer (2%) than bulk gold: V<\/em>0<\/sub> = 67.65(3) \u00c53<\/sup>, K<\/em>0<\/sub> = 170(3)GPa, at zero pressure.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> gold nanoparticles, hydrostatic pressure, nonhydrostatic effects, X-ray diffraction, small-angle X-ray scattering, specific volume at nanoscale, bulk modulus<\/p>\n\n\n\n

DOI:<\/strong> <\/a><\/a>10.1021\/acs.jpcc.1c08006<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Single-crystal elastic and thermodynamic properties of gamma-LiAlO2<\/summary>
\n

Author(s):<\/strong> E. Haussu\u0308hl, L. Bayarjargal, J. Ruiz-Fuertes<\/p>\n\n\n\n

Source:<\/strong> Journal of Applied Physics<\/p>\n\n\n\n

Volume:<\/strong> 129(14)   P\u00e1ginas:<\/strong> Journal of Applied Physics<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

The elastic properties of \ud835\udefe<\/em>-LiAlO2 were reinvestigated with the aid of resonant ultrasound spectroscopy (RUS) at ambient conditions. A strong discrepancy of the elastic coefficients derived by RUS can be found from the experimental results from the literature, where \ud835\udc50<\/em>12 and \ud835\udc50<\/em>13 deviate from our results by up to 60% (46\u2009GPa). In contrast to the experimental \ud835\udc50\ud835\udc56\ud835\udc57<\/em> from the literature, we can recognize a good agreement between the elastic coefficients derived from RUS and the values using density functional theory. The dielectric permittivity was measured on large plane-parallel plates, and the piezoelectric stress coefficient \ud835\udc52<\/em>123=0.14Cm\u22122 was derived from RUS measurements at ambient conditions. The heat capacity between 4 and 398\u2009K has been obtained by microcalorimetry using a relaxation calorimeter. The Debye temperature was derived from heat capacity measurements (\u0398Cp=676\u2009K) and RUS measurements (\u0398elastic=688 K).<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> <\/a><\/a>10.1021\/acs.jpcc.1c08006<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Compressibility and Phase Stability of Iron-Rich Ankerite<\/summary>
\n

Author(s):<\/strong> R. Chuli\u00e1-Jord\u00e1n, D. Santamaria-Perez, J. Ruiz Fuertes, A. Otero-De-La-Roza, C. Popescu<\/p>\n\n\n\n

Source:<\/strong> Minerals<\/p>\n\n\n\n

Volume:<\/strong> 11(6)   P\u00e1ginas:<\/strong> 607<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

The structure of the naturally occurring, iron-richmineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch\u2013Murnaghan equation of state yields V0 = 328.2(3) \u00c53, bulk modulus B0 = 89(4) GPa, and its first-pressure derivative B\u20190 = 5.3(8)\u2014values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO3)2 ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite- III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO3)2 ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> iron-rich ankerite; carbonate mineral; high pressure; phase transition; compressibility<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.3390\/min11060607<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Crystal Structure of BaCa(CO3)2 Alstonite Carbonate and Its Phase Stability upon Compression<\/summary>
\n

Author(s):<\/strong> R. Chuli\u00e1-Jord\u00e1n, D. Santamaria-Perez, J. Ruiz Fuertes, A. Otero-De-La-Roza, C. Popescu<\/p>\n\n\n\n

Source:<\/strong> ACS Earth and Space Chemistry<\/p>\n\n\n\n

Volume:<\/strong> 5  P\u00e1ginas:<\/strong> 1130-1139<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

New single-crystal X-ray diffraction experiments and density functional theory (DFT) calculations reveal that the crystal chemistry of the CaO\u2013BaO\u2013CO2<\/sub> system is more complex than previously thought. We characterized the BaCa(CO3<\/sub>)2<\/sub> alstonite structure at ambient conditions, which differs from the recently reported crystal structure of this mineral in the stacking of the carbonate groups. This structural change entails the existence of different cation coordination environments. The structural behavior of alstonite at high pressures was studied using synchrotron powder X-ray diffraction data and ab initio calculations up to 19 and 50 GPa, respectively. According to the experiments, above 9 GPa, the alstonite structure distorts into a monoclinic C<\/em>2 phase derived from the initial trigonal structure. This is consistent with the appearance of imaginary frequencies and geometry relaxation in DFT calculations. Moreover, calculations predict a second phase transition at 24 GPa, which would cause the increase in the coordination number of Ba atoms from 10 to 11 and 12. We determined the equation of state of alstonite (V<\/em>0<\/sub> = 1608(2) \u00c53<\/sup>, B<\/em>0<\/sub> = 60(3) GPa, B<\/em>\u20320<\/sub> = 4.4(8) from experimental data) and analyzed the evolution of the polyhedral units under compression. The crystal chemistry of alstonite was compared to that of other carbonates and the relative stability of all known BaCa(CO3<\/sub>)2<\/sub> polymorphs was investigated.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

alstonite, BaCa(CO3<\/sub>)2<\/sub>, crystal structure, carbonate, sphase transition, high pressure, synchrotron X-ray diffraction, DFT calculations<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.3390\/min11060607<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Unveiling the role of the lone electron pair in sesquioxides at high pressure: compressibility of beta-Sb2O3<\/summary>
\n

Author(s):<\/strong><\/p>\n\n\n\n

J. A. Sans, F. J. Manj\u00f3n, A. L. De Jes\u00fas Pereira, J. Ruiz Fuertes, C. Popescu, A. Mu\u00f1oz, P. Rodr\u00edguez-Hern\u00e1ndez, J. Pellicer-Porres, V. P. Cuenca-Gotor, J. Contreras-Garc\u00eda, J. Iba\u00f1ez, V. Monteseguro Padron<\/p>\n\n\n\n

Source:<\/strong> Dalton Transaction<\/p>\n\n\n\n

Volume:<\/strong> 50 (6)  P\u00e1ginas:<\/strong> 5493-5505<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

The structural, vibrational and electronic properties of the compressed \u03b2-Sb2<\/sub><\/small>O3<\/sub><\/small> polymorph, a.k.a. mineral valentinite, have been investigated in a joint experimental and theoretical study up to 23 GPa. The compressibility of the lattice parameters, unit-cell volume and polyhedral unit volume as well as the behaviour of its Raman- and IR-active modes under compression have been interpreted on the basis of ab initio<\/em> theoretical simulations. Valentinite shows an unusual compressibility up to 15 GPa with four different pressure ranges, whose critical pressures are 2, 4, and 10 GPa. The pressure dependence of the main structural units, the lack of soft phonons, and the electronic density charge topology address the changes at those critical pressures to isostructural phase transitions of degree higher than 2. In particular, the transitions at 2 and 4 GPa can be ascribed to the changes in the interaction between the stereochemically-active lone electron pairs of Sb atoms under compression. The changes observed above 10 GPa, characterized by a general softening of several Raman- and IR-active modes, point to a structural instability prior to the 1st-order transition occurring above 15 GPa. Above this pressure, a tentative new high-pressure phase (s.g. Pcc<\/em>2) has been assigned by single-crystal and powder X-ray diffraction measurements.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

<\/p>\n\n\n\n

DOI:<\/strong><\/p>\n\n\n\n

DOIhttps:\/\/doi.org\/10.1039\/D1DT00268F<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

((R)-()-3-Hydroxyquinuclidium)[FeCl4]; a plastic hybrid compound with chirality, ferroelectricity and long range magnetic ordering<\/summary>
\n

Author(s):<\/strong> P. Gonzalez Izquierdo, O. Fabelo Rosa, L.a Ca\u00f1adillas-Delgado, G. Beobide, O. Vallcorba, J. Salgado-Beceiro, M. S\u00e1nchez-And\u00fajar, C. Mart\u00edn, J. Ruiz Fuertes, J. Eduardo Garc\u00eda, M. Teresa Fern\u00e1ndez-D\u00edaz, M. De Pedro Del Valle<\/p>\n\n\n\n

Source:<\/strong> Journal of Materials Chemistry C<\/p>\n\n\n\n

Volume:<\/strong> 9 (13)  P\u00e1ginas:<\/strong> 4453-4465<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: Quinuclidinium salts and their derivatives are now in the focus of materials science as building units of multifunctional materials. Their properties can be easily switchable, allowing their use in a wide range of physical applications. One type of these kinds of materials, the homochiral hybrid halometallate ferroelectric compounds, is not well understood. In this work, (R<\/em>)-(\u2212)-3-quinuclidinol hydrochloride was used in the synthesis of ((R<\/em>)-(\u2212)-3-hydroxyquinuclidium)[FeCl4<\/sub><\/small>]. The use of this enantiomeric cation forces crystallographic non-centrosymmetry, which was confirmed by polarimetry and circular dichroism spectroscopy. We studied the physical properties of this compound at different temperatures by single crystal, synchrotron and neutron powder X-ray diffraction, which showed a rich series of structural and magnetic phase transitions. From synchrotron powder X-ray diffraction data, a plastic phase was observed above 370 K (phase I). Between 370 K and ca.<\/em> 310 K, an intermediate polar phase was detected, solved in a non-centrosymmetric polar space group (C<\/em>2) (phase II). Below ca.<\/em> 310 K, the compound crystallizes in the triclinic P<\/em>1 non-centrosymmetric space group (phase III) which is maintained down to 4 K, followed by phase IV, which shows tridimensional magnetic ordering. The temperature evolution of the neutron diffraction data shows the appearance of new reflections below 4 K. These reflections can be indexed to a commensurate propagation vector k<\/strong> = (0, 0, \u00bd). The magnetic structure below T<\/em>N<\/sub><\/small> was solved in the P<\/em>s<\/sub><\/small>1 Shubnikov space group, which gives rise to an antiferromagnetic structure, compatible with the magnetometry measurements. Near room temperature, the crystal phase transition is associated with a dielectric change. In particular, the phase transition between phase III (S.G.:P<\/em>1) and phase II (S.G.:C<\/em>2) involves an increase of symmetry between two non-centrosymmetric space groups. Therefore, it allows, by symmetry, the emergence of ferroelectric and ferroelastic ordering. Piezoresponse force microscopy (PFM) imaging measurements provided evidence for polarization switching and a local ferroelectric behavior of phase III at room temperature. Additionally, the obtained butterfly curve and hysteresis loop by PFM exhibits a low coercive voltage of \u223c10 V. This value is remarkable, since it approaches those obtained for materials with application in ferroelectric random access memories (FeRAMs).<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> <\/p>\n\n\n\n

<\/p>\n\n\n\n

DOI<\/strong> <\/a>https:\/\/doi.org\/10.1039\/D0TC05800A<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Modification of the spectroscopic properties of Tb2O3 phosphor under the high-pressure phase transitions sequence.<\/summary>
\n

Author(s):<\/strong> M. T. Candela, F. Aguado, J. Gonz\u00e1lez-Lav\u00edn, J. A. Gonz\u00e1lez, and R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 859  P\u00e1ginas:<\/strong> 157899<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: The high-pressure behavior of cubic Tb2<\/sub>O3<\/sub> phase (C-type) has been investigated by in situ<\/em> photoluminescence<\/a> and Raman spectroscopy<\/a> up to 18 GPa and 22 GPa, respectively. The luminescence spectrum of Tb2<\/sub>O3<\/sub> at ambient conditions shows its characteristic sharp-line emission bands with the most intense one corresponding to the 5<\/sup>D4<\/sub> – 7<\/sup>F5<\/sub> transition, responsible for the green emission. Excitation and emission spectra measured at low temperature and at different emission and excitation wavelengths suggest that photoluminescence is governed by the Tb3+<\/sup> in the non-centrosymmetric site (C2<\/sub>). A phase transition between 7.2 and 8.6 GPa is observed by Raman and photoluminescence experiments and is associated with a cubic-to-monoclinic (B-type) structural transformation. From 14 GPa the predominant modes in the Raman spectrum correspond to those from the trigonal phase (A-type), indicating that the pressure-induced structural phase transition sequence of Tb2<\/sub>O3<\/sub> is C \u2192 B \u2192 A. Upon pressure release, the starting cubic phase is not recovered, but the monoclinic one.<\/p>\n\n\n\n

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KeyWords Plus:<\/strong> Phosphors, High-pressure, Phase transitions, Luminescence, Inelastic light scattering<\/p>\n\n\n\n

<\/p>\n\n\n\n

DOI<\/strong>: https:\/\/doi.org\/10.1016\/j.jallcom.2020.157899<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure dependence of the crystal-field spectrum of KNiF3: Single and double excitations<\/summary>
\n

Author(s):<\/strong> A. Barreda-Argu\u0308eso, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Physical Review B<\/p>\n\n\n\n

Volume:<\/strong> 103(8)  P\u00e1ginas:<\/strong> 085115<\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: This work investigates the Ni-F distance dependence of the crystal-field (CF) transitions of Ni2+ in KNiF3 by high-pressure spectroscopy. All peaks shift to higher energy with pressure according to trends foreseen by the Tanabe-Sugano diagram. At ambient conditions, we obtain Racah and CF splitting parameters of B=0.118eV, 10Dq=0.908eV; C\/B=4.4 (10Dq\/B=7.7). B and 10Dq vary with pressure as \u2202B\u2202P=\u20130.11meVGPa\u20131 and \u220210Dq\u2202P=24meVGPa\u20131. Similar to KCoF3, the slight decrease of B with pressure reflects the strong ionic character of the Ni-F bond and its high stability against compression. We have correlated the measured pressure dependence of 10Dq with the Ni-F bond distance, showing that it follows a potential law as 10Dq=CR\u2013n with an exponent n=6.6\u00b10.5, thus providing experimental data for checking the suitability of theoretical models aiming to explain the slight deviations of observed R dependencies of 10Dq from the CF theory (n=5). We have applied the experimental 10Dq(R) relationship to determine the real Ni-F bond distances in fluoroperovskites ABF3:Ni2+ from the spectroscopically measured 10Dq as an alternative method for determining bond distances, RNi\u2212F, in impurity systems. We show that the so-obtained RNi\u2212F deviates from the bond distance of the host site, RB\u2212F, proportionally to the difference RB\u2212F\u2212R0, with R0 being the sum of ionic radii RF\u2212+RNi2+.<\/p>\n\n\n\n

<\/h4>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> High-pressure, Phase transitions<\/p>\n\n\n\n

<\/p>\n\n\n\n

DOI<\/strong>:<\/a>10.1103\/PhysRevB.103.085115<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

2020<\/strong><\/p>\n\n\n\n

A custom-made functionalization method to control the biological identity of nanomaterials<\/summary>
\n

Author(s):<\/strong> E. Pad\u00edn-Gonz\u00e1lez, E. Navarro-Palomares, L. Valdivia, N. Iturrioz-Rodr\u00edguez, M. A. Correa, R. Valiente<\/strong>, M. L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> Nanomedicine, Nanotechnology, Biology, and Medicine<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

<\/p>\n\n\n\n

Abstract<\/strong>: Here we propose a one-step strategy to endow nanomaterials with a custom-designed bio-identity. This study designs a universal ‘nanomaterial binding domain’ that can be genetically attached to any protein ensuring precise and spontaneous protein orientation. We demonstrate how, despite the simplicity of the method, the bioconjugation achieved: (i) is highly efficient, even in the presence of competing proteins, (ii) is stable at extreme physiological conditions (pH ranges 5.2-9.0; NaCl concentrations 0-1 M); (iii) prevents unwanted protein biofouling days after incubation in biologically-relevant conditions; and finally, (iv) avoids nanoparticle interaction with promiscuous unspecific receptors. In summary, this protein biocoating technique, applicable to a wide array of nano-designs, integrates material science and molecular biology procedures to create hybrid nanodevices with well-defined surfaces and predictable biological behaviors, opening a chapter in precision nanodiagnostics, nanosensing or nanotherapeutic applications.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Biofouling; Biotechnology; Chimera protein; Electrostatic interaction; Nano\u2013bio interface.<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.nano.2020.102268<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Exploiting optical properties of nanopolycrystalline diamond in high pressure experiments<\/summary>
\n

Author(s):<\/strong> J. A. Barreda-Arg\u00fceso, J. Gonz\u00e1lez, R. Valiente, T. Irifune and F. Rodr\u00edguez <\/p>\n\n\n\n

Source:<\/strong> High Pressure Research<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 40   P\u00e1ginas:<\/strong> 117-118<\/p>\n\n\n\n

Abstract<\/strong>: We investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray\/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvil Cell (MAC). The results are compared with those obtained in a DAC, where Raman signals from NPD chips and diamond anvils strongly overlap. Its pressure behaviour in the hydrostatic and non-hydrostatic regimes were investigated. We showed that the nanopolycrystalline structure induces remarkable differences in the peak shift and broadening between NPD and natural type IIa single-crystal diamond, making NPD suitable as pressure gauge for pressure determination and testing hydrostaticity of pressure transmitting medium.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Raman spectroscopy Luminescence Pressure gauge Pressure sensitivity Nanopolycrystalline diamond<\/p>\n\n\n\n

DOI:<\/strong><\/a> <\/a>10.1080\/08957959.2019.1702173<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Plasmonic Sensing of Refractive Index and Density in Methanol\u2013Ethanol Mixtures at High Pressure<\/summary>
\n

Author(s):<\/strong> C. Mart\u00edn-S\u00e1nchez<\/strong>, A. S\u00e1nchez-Iglesias, P. Mulvaney, L. M. Liz-Marz\u00e1n, and F. Rodr\u00edguez<\/strong><\/p>\n\n\n\n

Source:<\/strong> The Journal of Physical Chemistry C<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 124 (16)   P\u00e1ginas:<\/strong> 8978-8983<\/p>\n\n\n\n

Abstract<\/strong>: The localized surface plasmon resonance (LSPR) of gold nanospheres dispersed in methanol\u2013ethanol 4:1 was measured as a function of pressure up to 60 GPa. The LSPR exhibits an intense red-shift with pressure in the range of 0\u201310 GPa, followed by a slower blue-shift at higher pressures. This is because an increase in the solvent refractive index with pressure leads to a red-shift of the LSPR peak wavelength while an increase in the electron density of the gold nanospheres with pressure leads to a blue-shift. Solvent solidification at 10 GPa and associated nonhydrostatic effects have a negligible influence on the LSPR shifts in the case of nanospheres. Here we show that both the LSPR shifts and changes in the nanospheres absorption coefficient can be explained on the basis of Gans\u2019 model, and this enables the solvent refractive index and the density of the solvent to be determined across the hydrostatic pressure range from 0 to 60 GPa. Interestingly, plasmonic sensing shows no evidence of crystallization or glass phase transitions in MeOH\u2013EtOH 4:1 within the explored pressure range.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Metal nanoparticles, Gold, Optical properties, Surface plasmon resonance, Solvents<\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1021\/acs.jpcc.0c01419<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Dye-doped biodegradable nanoparticle SiO2 coating on zinc- and iron-oxide nanoparticles to improve biocompatibility and for in vivo imaging studies<\/summary>
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Author(s):<\/strong> E. Navarro-Palomares, P. Gonz\u00e1lez-Saiz, C. Renero-Lecuna, R. Mart\u00edn-Rodr\u00edguez, F. Aguado<\/strong>, D. Gonz\u00e1lez-Alonso, L. Fern\u00e1ndez-Barqu\u00edn, J. Gonz\u00e1lez<\/strong>, M. Ba\u00f1obre-L\u00f3pez, M. L. Fanarraga, R. Valiente<\/strong><\/p>\n\n\n\n

Source:<\/strong> Nanoscale<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 12   P\u00e1ginas:<\/strong> 378876164-6175<\/p>\n\n\n\n

Abstract<\/strong>: In vivo imaging and therapy represent one of the most promising areas in nanomedicine. Particularly, the identification and localization of nanomaterials within cells and tissues are key issues to understand their interaction with biological components, namely their cell internalization route, intracellular destination, therapeutic activity and possible cytotoxicity. Here, we show the development of multifunctional nanoparticles (NPs) by providing luminescent functionality to zinc and iron oxide NPs. We describe simple synthesis methods based on modified St\u00f6ber procedures to incorporate fluorescent molecules on the surface of oxide NPs. These procedures involve the successful coating of NPs with size-controlled amorphous silica (SiO2<\/sub><\/small>) shells incorporating standard chromophores like fluorescein, rhodamine B or rhodamine B isothiocyanate. Specifically, spherical Fe3<\/sub><\/small>O4<\/sub><\/small> NPs with an average size of 10 nm and commercial ZnO NPs (ca. 130 nm), both coated with an amorphous SiO2<\/sub><\/small> shell of ca. 15 and 24 nm thickness, respectively, are presented. The magnetic nanoparticles, with a major presence of magnetite, show negligible coercitivity. Hence, interactions (dipolar) are very weak and the cores are in the superparamagnetic regime. Spectroscopic measurements confirm the presence of fluorescent molecules within the SiO2<\/sub><\/small> shell, making these hybrid NPs suitable for bioimaging. Thus, our coating procedures improve NP dispersibility in physiological media and allow the identification and localization of intracellular ZnO and Fe3<\/sub><\/small>O4<\/sub><\/small> NPs using confocal microscopy imaging preserving the fluorescence of the NP. We demonstrate how both Fe3<\/sub><\/small>O4<\/sub><\/small> and ZnO NPs coated with luminescent SiO2<\/sub><\/small> are internalized and accumulated in the cell cytoplasm after 24 hours. Besides, the SiO2<\/sub><\/small> shell provides a platform for further functionalization that enables the design of targeted therapeutic strategies. Finally, we studied the degradation of the shell in different physiological environments, pointing out that the SiO2<\/sub><\/small> coating is stable enough to reach the target cells maintaining its original structure. Degradation took place only 24 hours after exposure to different media.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> <\/a>https:\/\/doi.org\/10.1039\/C9NR08743E<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-and Temperature Induced Phase Transitions, Piezochromism, NLC Behaviour and Pressure Controlled Jahn-Teller Switching in a Cu-based Framework<\/summary>
\n

Author(s):<\/strong> C. McMonagle, P. Comar, G. S. Nichol, D. R. Allan, J. A. Barreda-Arg\u016beso, J. A. Gonzalez, F. Rodriguez, R. Valiente, <\/strong>G. Turner, E. K. Brechin and St. A. Moggach<\/p>\n\n\n\n

Source:<\/strong> Chemical Science<\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 11   P\u00e1ginas:<\/strong> 3788793-8799<\/p>\n\n\n\n

Abstract<\/strong>: In situ<\/em> single-crystal diffraction and spectroscopic techniques have been used to study a previously unreported Cu-framework bis[1-(4-pyridyl)butane-1,3-dione]copper(II<\/small>) (CuPyr-I). CuPyr-I was found to exhibit high-pressure and low-temperature phase transitions, piezochromism, negative linear compressibility, and a pressure induced Jahn\u2013Teller switch, where the switching pressure was hydrostatic media dependent.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1039\/D0SC03229H<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Comment on \u201cCopper-Substituted Lead Perovskite Materials Constructed with Different Halides for Working (CH3NH3)2CuX4\u2010Based Perovskite Solar Cells from Experimental and Theoretical View\u201d<\/summary>
\n

Author(s):<\/strong> R. Valiente and F. Rodriguez<\/p>\n\n\n\n

Source:<\/strong> JACS Applied Materials & Interfaces<\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 12   P\u00e1ginas:<\/strong> 37807-37810<\/p>\n\n\n\n

Abstract<\/strong>: In recent years, two-dimensional perovskites have received considerable attention for their potential applications for optoelectronics. Contrary to previous publications, we demonstrate that (CH3<\/sub>NH3<\/sub>)2<\/sub>CuCl4<\/sub> hybrid organic\u2013inorganic layered perovskite does not show any room-temperature photoluminescence (PL) under UV excitation. This statement can be extended to other perovskites with general formula AMX<\/em>3<\/sub> or A<\/em>2<\/sub>MX<\/em>4<\/sub>, based on M<\/em>: Cu2+<\/sup> and X<\/em>: Cl\u2013<\/sup> or Br\u2013<\/sup>. These materials, the object of increasing interest because of their efficient light absorption in a wide UV\u2013vis\u2013NIR range ideal for solar cells and optoelectronics, lack PL at room temperature, in contrast to recent findings reporting PL properties in this and other similar Cu2+<\/sup>-related materials.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Absorption, Crystal structure, Solar cells, Optoelectronics, Perovskites<\/p>\n\n\n\n

DOI: <\/a>https:\/\/doi.org\/10.1021\/acsami.0c11480<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Exploring pressure effects on metallic nanoparticles and surrounding media through plasmonic sensing<\/summary>
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Author(s):<\/strong> C. Mart\u00edn-S\u00e1nchez, S. Seibt, J. A. Barreda-Argu\u0308eso and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physics: Conference Series<\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 1609(1)   P\u00e1ginas:<\/strong> 012009 (7p)<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

The sensing capabilities of gold nanorods under high-pressure conditions were investigated in methanol-ethanol mixtures (up to 13 GPa) and in water (up to 9 GPa) through their optical extinction. The longitudinal SPR band of AuNR exhibits a redshift with pressure which is the result of two main competing effects: compression of the conduction electrons which increases the bulk plasma frequency (blueshift) and increase in the solvent density (redshift). The variation in de SPR peak wavelength allows us to estimate the bulk modulus of the gold nanoparticles with a precision of 10 % and to obtain analytical functions providing the pressure dependence of the refractive index of water in three phases: liquid, ice VI and ice VII. Furthermore, the SPR band shows abrupt jumps at the liquid to ice phase VI and ice phase VII transitions, which are in accordance with the first-order character of these transitions.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong><\/p>\n\n\n\n

DOI: 10.1088\/1742-6596\/1609\/1\/012009<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High Pressure optical nanothermometer based on Er3+ photoluminescence<\/summary>
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Author(s):<\/strong> V. Guti\u00e9rrez-Cano, R. Valiente, J.A. Gonz\u00e1lez, and F. Rodriguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physics: Conference Series<\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 1609(1)   P\u00e1ginas:<\/strong> 12004 (9p)<\/p>\n\n\n\n

Abstract<\/strong>: <\/p>\n\n\n\n

The optical properties of a sparsely investigated material, LaGdO3 doped with Er3+, are explored regarding its suitability as nanothermometer. Besides its excellent capabilities for dielectric applications, when doping with Er3+, this material provides a highly efficient upconversion photoluminescence (PL) for high temperature thermometry at high pressure due to its structural stability. LaGdO3 belongs to the perovskite-type ABO3 compounds with a B-type monoclinic C2\/m space group (a = 14.43 \u00c5; b = 3.69 \u00c5; c = 9.00 \u00c5; and \u03b2 = 100.70\u00ba) at ambient conditions. It undergoes a structural phase transition to a hexagonal \ud835\udc433#\ud835\udc5a1 phase at 3 GPa yielding a notable PL enhancement, thus enabling it as a potential high-pressure hightemperature nanothermometer.<\/p>\n\n\n\n

<\/p>\n\n\n\n

KeyWords Plus:<\/strong><\/p>\n\n\n\n

DOI: doi:10.1088\/1742-6596\/1609\/1\/012004<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

CaCu3Ti4O12: pressure dependence of electronic and vibrational structures<\/summary>
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Author(s):<\/strong> E. Jara, J. Gonz\u00e1lez, F. Aguado, R. Valiente and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physics: Conference Series<\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 1609(1)   P\u00e1ginas:<\/strong> 12005 (7p)<\/p>\n\n\n\n

Abstract<\/strong>: The effects of pressure in electronic and vibrational properties of the double perovskite CaCu3Ti4O12 have been investigated in the 0-25 GPa range by optical absorption and Raman spectroscopy. Besides a full structural characterization, we aim at unveiling whether the ambient Im3 crystal structure is stable under high pressure conditions and how its giant dielectric permitivity and electronic gap varies with pressure. Results show that there is evidence of neither structural phase transition nor metallization in CaCu3Ti4O12 in the explored pressure range. We have observed the eight Raman active modes associated with its Im3 crystal phase and obtained their corresponding frequency and pressure shift. Moreover, the direct electronic band gap (2.20 eV), which is mainly associated with the oxygen-to-copper charge transfer states, increases slightly with pressure at a rate of 13 meV GPa?1 from 0 to 10 GPa. Above this pressure is almost constant (Eg = 2.3 eV). The results highlight the high stability of the compound in its Im3 phase against compression.<\/sup><\/p>\n\n\n\n

KeyWords Plus:<\/strong>DOI:<\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/1742-6596\/1609\/1\/012005<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Effect of TiO2 and ZnO Nanoparticles on the Performance of Dielectric Nanofluids Based on Vegetable Esters During Their Aging<\/summary>
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Author(s):<\/strong> I. Fern\u00e1ndez, R. Valiente, F. Ortiz, C. J. Renedo, A. Ortiz<\/p>\n\n\n\n

Source:<\/strong> Nanomaterials<\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 10   P\u00e1ginas:<\/strong> 692 (18p)<\/p>\n\n\n\n

Abstract:<\/strong> Over the last few decades the insulating performance of transformer oils has been broadly studied under the point of view of nanotechnology, which tries to improve the insulating and heat dissipation performance of transformer oils by suspending nanoparticles. Many authors have analyzed the thermal and dielectric behavior of vegetable oil based-nanofluids, however, very few works have studied the evolution of these liquids during thermal aging and their stability. In this paper has been evaluated the performance of aged vegetable oil based-nanofluids, which have been subjected to accelerated thermal aging at 150 \u00b0C. Nanoparticles of TiO2<\/sub> and ZnO have been dispersed in a commercial natural ester. Breakdown voltage, resistivity, dissipation factor and acidity of nanofluid samples have been measured according to standard methods, as well as stability. Moreover, it has been analyzed the degradation of Kraft paper through the degree of polymerization (DP). The results have showed that although nanoparticles improve breakdown voltage, they increase the ageing of insulation liquids and dielectric paper.<\/sup><\/p>\n\n\n\n

KeyWords Plus:<\/strong> Energy and Catalysis<\/p>\n\n\n\n

 DOI:<\/a> <\/a>https:\/\/doi.org\/10.3390\/nano10040692<\/a><\/strong><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

A Comparative Study on Luminescence Properties of Y2O3: Pr3+ Nanocrystals Prepared by Different Synthesis Methods,<\/summary>
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Author(s):<\/strong> A. Diego-Rucabado, M. T. Candela, F. Aguado, J. Gonz\u00e1lez, F. Rodr\u00edguez, R. Valiente, R. Mart\u00edn-Rodr\u00edguez, I. Cano<\/p>\n\n\n\n

Source:<\/strong> Nanomaterials<\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 10   P\u00e1ginas:<\/strong> 1574 (20p)<\/p>\n\n\n\n

Abstract:<\/strong> Pr3+<\/sup>-doped Y2<\/sub>O3<\/sub> nanocrystals (NCs) have been obtained via five wet-chemistry synthesis methods which were optimized in order to achieve superior optical properties. To this end, a systematic study on the influence of different reaction parameters was performed for each procedure. Specifically, precursor concentration, reaction temperature, calcination temperature, and time, among others, were analyzed. The synthesized Y2<\/sub>O3<\/sub>: Pr3+<\/sup> NCs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and reflectance and Raman spectroscopy. In addition, the optical properties of such NCs were investigated by excitation, emission, and luminescence decay measurements. Concretely, emission from the 1<\/sup>D2<\/sub> level was detected in all samples, while emission from 3<\/sup>PJ<\/sub> was absent. Finally, the effect of the synthesis methods and the reaction conditions on the luminescence decay has been discussed, and a comparative study of the different methods using the fluorescence lifetime of so-obtained Y2<\/sub>O3<\/sub>: Pr3+<\/sup> NCs as a figure of merit has been carried out<\/sup><\/p>\n\n\n\n

KeyWords Plus:<\/strong> S\u00edntesis and Characterization of Nanoparticles with Luminescence Properties<\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: <\/a>https:\/\/doi.org\/10.3390\/nano10081574<\/a><\/strong><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Nanomechanics of graphene oxide-bacteriophage based self-assembled porous composites.<\/summary>
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Author(s):<\/strong> Yiwei Sun, Paolo Passaretti, Ignacio Hernandez<\/em>, Jesus Gonzalez, Wei Liu, Fernando Rodriguez, David J. Dunstan, Pola Goldberg O ppenheimer6 & Colin J. Humphreys<\/p>\n\n\n\n

Source:<\/strong> Scientific reports<\/em><\/p>\n\n\n\n

Volume:<\/strong> 10(1)   P\u00e1ginas:<\/strong> 1-8<\/p>\n\n\n\n

Abstract:<\/strong> Graphene oxide, integrated with the filamentous bacteriophage M13, forms a 3D large-scale multifunctional porous structure by self-assembly, with considerable potential for applications. We performed Raman spectroscopy under pressure on this porous composite to understand its fundamental mechanics. The results show that at low applied pressure, the \ud835\udc60\ud835\udc5d<\/em>2 bonds of graphene oxide stiffen very little with increasing pressure, suggesting a complicated behaviour of water intercalated between the graphene layers. The key message of this paper is that water in a confined space can have a significant impact on the nanostructure that hosts it. We introduced carbon nanotubes during the self-assembly of graphene oxide and M13, and a similar porous macro-structure was observed. However, in the presence of carbon nanotubes, pressure is transmitted to the \ud835\udc60\ud835\udc5d<\/em>2 bonds of graphene oxide straightforwardly as in graphite. The electrical conductivity of the composite containing carbon nanotubes is improved by about 30 times at a bias voltage of 10 V. This observation suggests that the porous structure has potential in applications where good electrical conductivity is desired, such as sensors and batteries.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: https:\/\/doi.org\/10.1038\/s41598-020-72372-1<\/a><\/strong><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Structural Correlations in Jahn\u2013Teller Systems of Mn3+ and Cu2+: Unraveling Local Structures through Spectroscopic Techniques<\/summary>
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Author(s):<\/strong> M. T. Candela, E. Jara, F. Aguado, R. Valiente, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Inorganic Chemistry<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 124    P\u00e1ginas:<\/strong> 22692-22703<\/p>\n\n\n\n

Abstract:<\/strong> An experimental correlation study between the low-symmetry 3d orbital splitting pattern, \u0394e<\/sub> and \u0394t<\/sub>, determined by optical spectroscopy, and the local distortion \u03c1, determined by X-ray diffraction, for different Cu2+<\/sup> and Mn3+<\/sup> fluorides and chlorides is presented. Single crystals of different dimensionalities were explored, some of them studied under high-pressure conditions. The collection of structural and spectroscopic data provides structural correlations relating \u03c1 and \u0394e<\/sub> and \u0394t<\/sub> in Cu2+<\/sup> and Mn3+<\/sup> systems, showing that \u0394e<\/sub> (and \u0394t<\/sub>) scales with \u03c1. Such correlations can be used to estimate local distortions of Cu2+<\/sup> (or Mn3+<\/sup>) introduced as impurities in different chloride and fluoride host lattices from spectroscopic data. The results can be interpreted in the framework of the Jahn\u2013Teller theory and provide support for the proposed structural scenario. The influence of the crystal anisotropy in the local structure is analyzed as well and compared with transition metal ion systems having E<\/em>\u2297e<\/em> Jahn\u2013Teller (Cu2+<\/sup>, Mn3+<\/sup>) and singly orbital (Ni2+<\/sup>, Mn2+<\/sup>, Fe3+<\/sup>) ground states in octahedral symmetry.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Group theory, Crystals, Anions, Transition metals, Ions<\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: https:\/\/doi.org\/10.1021\/acs.jpcc.0c07243<\/a><\/strong><\/p>\n\n\n\n

<\/p>\n\n\n\n

Comparative study of the high-pressure behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8<\/summary>
\n

Author(s):<\/strong> <\/p>\n\n\n\n

D. D\u00edaz-Anichtchenko, D. Santamaria-Perez, T. Marque\u00f1o, J. Pellicer-Porres, J. Ruiz-Fuertes, R. Ribes, J. Iba\u00f1ez, S.N. Achary, C. Popescu, D. Errandonea<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 837    P\u00e1ginas:<\/strong> 1555052<\/p>\n\n\n\n

Abstract:<\/strong> We report a study of the high-pressure structural behavior of ZnV2<\/sub>O6<\/sub>, Zn2<\/sub>V2<\/sub>O7<\/sub>, and Zn3<\/sub>V2<\/sub>O8<\/sub>, which has been explored by means of synchrotron powder x-ray diffraction. We found that ZnV2<\/sub>O6<\/sub> and Zn3<\/sub>V2<\/sub>O8<\/sub> remain in the ambient-pressure structure up to 15 GPa. In contrast, in the same pressure range, Zn2<\/sub>V2<\/sub>O7<\/sub> undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa, respectively. Possible crystal structures for the first and second high-pressure phases are proposed. Reasons for the distinctive behavior of Zn2<\/sub>V2<\/sub>O7<\/sub> are discussed. The compressibility<\/a> of the different polymorphs has been determined. The response to pressure is found to be anisotropic in all the considered compounds and the room-temperature equations of state have been determined. The bulk moduli<\/a> of ZnV2<\/sub>O6<\/sub> (129(2) GPa) and Zn3<\/sub>V2<\/sub>O8<\/sub> (120(2) GPa) are consistent with a structural framework composed of compressible ZnO6<\/sub> octahedra and uncompressible VO4<\/sub> tetrahedra. In contrast, Zn2<\/sub>V2<\/sub>O7<\/sub> is highly compressible with a bulk modulus of 58(9) GPa, which is almost half of the bulk modulus of the other two vanadates<\/a>. The large compressibility of Zn2<\/sub>V2<\/sub>O7<\/sub> and its sequence of structural transitions are related to the fact that this material is less dense than the other zinc vanadates and to the penta-coordination of Zn atoms by oxygen atoms in Zn2<\/sub>V2<\/sub>O7<\/sub>. A comparison to the high-pressure behavior of related compounds is presented.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Vanadates, High pressure, X-ray diffraction, Phase transitions, Equation of state<\/p>\n\n\n\n

 DOI: <\/strong>https:\/\/doi.org\/10.1016\/j.jallcom.2020.155505<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-Induced Polymerization of Polycyclic Arene\u2013Perfluoroarene Cocrystals: Single Crystal X-ray Diffraction Studies, Reaction Kinetics, and Design of Columnar Hydrofluorocarbons<\/summary>
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Author(s):<\/strong> <\/p>\n\n\n\n

A. Friedrich, I. E. Collings, K. F. Dziubek, S. Fanetti, K. Radacki, J. Ruiz-Fuertes, J. Pellicer-Porres, M. Hanfland, D. Sieh, R. Bini, S. J. Clark, T. B. Marder<\/p>\n\n\n\n

Source:<\/strong> J. Am. Chem. Soc<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 142    P\u00e1ginas:<\/strong> 18907-18923<\/p>\n\n\n\n

Abstract:<\/strong> Pressure-induced polymerization of aromatic compounds leads to novel materials containing sp3<\/sup> carbon-bonded networks. The choice of the molecular species and the control of their arrangement in the crystal structures via intermolecular interactions, such as the arene\u2013perfluoroarene interaction, can enable the design of target polymers. We have investigated the crystal structure compression and pressure-induced polymerization reaction kinetics of two polycyclic 1:1 arene\u2013perfluoroarene cocrystals, naphthalene\/octafluoronaphthalene (NOFN) and anthracene\/octafluoronaphthalene (AOFN), up to 25 and 30 GPa, respectively, using single-crystal synchrotron X-ray diffraction, infrared spectroscopy, and theoretical computations based on density-functional theory. Our study shows the remarkable pressure stability of the parallel arene\u2013perfluoroarene \u03c0-stacking arrangement and a reduction of the interplanar \u03c0-stacking separations by ca. 19\u201322% before the critical reaction distance is reached. A further strong, discontinuous, and irreversible reduction along the stacking direction at 20 GPa in NOFN (18.8%) and 25 GPa in AOFN (8.7%) indicates the pressure-induced breakdown of \u03c0-stacking by formation of \u03c3-bonded polymers. The association of the structural distortion with the occurrence of a chemical reaction is confirmed by a high-pressure kinetic study using infrared spectroscopy, indicating one-dimensional polymer growth. Structural predictions for the fully polymerized high-pressure phases consisting of highly ordered rods of hydrofluorocarbons are presented based on theoretical computations, which are in excellent agreement with the experimentally determined unit-cell parameters. We show that the polymerization takes place along the arene\u2013perfluoroarene \u03c0-stacking direction and that the lateral extension of the columns depends on the extension of the arene and perfluoroarene molecules.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Aromatic compounds, Crystal structure, Hydrocarbons, Phase transitions, Polymerization<\/p>\n\n\n\n

 DOI: <\/strong>https:\/\/pubs.acs.org\/doi\/10.1021\/jacs.0c09021<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced amorphization of the Y3Ga5O12 garnet studied to 1 Mbar<\/summary>
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Author(s):<\/strong> <\/p>\n\n\n\n

V. Monteseguro, J. Ruiz-Fuertes, M. Berkowski, G. L. Garbarino<\/p>\n\n\n\n

Source:<\/strong> Journal of Alloys and Compounds<\/p>\n\n\n\n

Volume:<\/strong> 830    P\u00e1ginas:<\/strong> 15467<\/p>\n\n\n\n

Abstract:<\/strong> We use micro-beam synchrotron x-ray diffraction to study the pressure-induced amorphization<\/a> of nano-sized and single crystals of Y3<\/sub>Ga5<\/sub>O12<\/sub> up to pressures exceeding 1 Mbar in static compression. The abrupt pressure-induced amorphization found for both 56 nm and bulk micrometric crystals at around 76 GPa independently of the pressure transmitting medium employed demonstrates its intrinsic nature, previously predicted at 79 GPa by ab initio<\/em> calculations. The single crystal structural solution at 50 GPa shows that the contraction of the unit-cell, mostly accommodated by the compressible YO8<\/sub> dodecahedra, gives rise to a regularization and tilting increase of the GaO6<\/sub> polyhedra with the Y\u2013O-Ga angle changing from 104.84\u00b0 to 102.34\u00b0 in 50 GPa. We obtain a bulk modulus<\/a> of 178(3) GPa for the single crystal and 172(3) GPa for the nanocrystals<\/a> in excellent agreement with previous calculations.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Garnets, Pressure, X-ray diffraction, Amorphization<\/p>\n\n\n\n

 DOI: <\/strong>https:\/\/doi.org\/10.1016\/j.jallcom.2020.154678<\/a><\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure and Temperature Effects on Low-Density Mg3Ca(CO3)4 Huntite Carbonate<\/summary>
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Author(s):<\/strong> D. Santamaria-Perez, A. Otero-De-La-Roza, J. Ruiz-Fuertes, R. Chulia-Jordan, T. Marque\u00f1o, S. Macleod, C. Popescu<\/p>\n\n\n\n

Source:<\/strong> J. Phys. Chem. C<\/p>\n\n\n\n

Volume:<\/strong> 124    P\u00e1ginas:<\/strong> 1077-1087<\/p>\n\n\n\n

Abstract:<\/strong> Pressure (P<\/em>)\u2013volume (V<\/em>)\u2013temperature (T<\/em>) relations of huntite [Mg3<\/sub>Ca(CO3<\/sub>)4<\/sub>] have been determined in situ up to 5 GPa and 500 \u00b0C using a resistive-heated diamond-anvil cell and synchrotron X-ray diffraction. Three runs were carried out: (i) compression at room temperature, (ii) heating at room pressure, and (iii) heating under compression. Experiments have been complemented with density functional theory calculations. The experimental (theoretical) bulk modulus of huntite is B<\/em>0<\/sub> = 102.6(2) GPa (99.55 GPa) with a first-pressure derivative of B<\/em>\u20320<\/sub> = 4.5(2) (4.483). The atomic distribution in space and the different compressibilities of [MgO6<\/sub>] octahedra and [CaO6<\/sub>] trigonal prisms in the R<\/em>32 rhombohedral unit cell cause a strongly anisotropic compressibility. The axial compressibilities are 1.91(2) \u00d7 10\u20133<\/sup> GPa\u20131<\/sup> (2.395 \u00d7 10\u20133<\/sup> GPa\u20131<\/sup>) and 4.52(5) \u00d7 10\u20133<\/sup> GPa\u20131<\/sup> (4.405 \u00d7 10\u20133<\/sup> GPa\u20131<\/sup>) for the a<\/em> and c<\/em> axes, respectively. The volumetric thermal expansion of huntite at low pressures is estimated to be 2.21(4) \u00d7 10\u20135<\/sup> K\u20131<\/sup> (2.95 \u00d7 10\u20135<\/sup> K\u20131<\/sup>), slightly lower than for calcite, magnesite, and dolomite. No phase transition was observed in the studied P<\/em>\u2013T<\/em> range. The decomposition of huntite into CaCO3<\/sub>, MgO, and CO2<\/sub> occurs at \u223c410 \u00b0C independently of pressure when the sample is heated at 2 \u00b0C\/min, but it is strongly dependent on the heating rate (i.e., the higher the heating rate, the higher the temperature at which decomposition starts). The crystal chemistry and phase stability of huntite are compared to those of other carbonates.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 DOI:<\/strong> 10.1021\/acs.jpcc.9b08952<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n<\/div><\/details><\/div>\n\n\n\n

2019<\/strong><\/p>\n\n\n\n

Multi-walled carbon nanotubes complement the anti-tumoral effect of 5-Fluorouracil<\/summary>
\n

Author(s):<\/strong> E. Gonz\u00e1lez-Lavado, L. Valdivia, A. Garcia-Casta\u00f1o, F. Gonz\u00e1lez<\/strong>, C. Pesquera, R. Valiente<\/strong>, and M.L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> Oncotarget<\/em><\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 10    P\u00e1ginas:<\/strong> 2022-2029<\/p>\n\n\n\n

Abstract:<\/strong> Isolation of high-level radioactive waste (HLW) in deep geological repositories (DGR) through a multibarrier concept is the most accepted approach to ensure long-term safety. Clay minerals are one of the most promising materials to be used as engineered barriers. In particular, high charge micas, as components of the engineered barrier, show superselectivity for some radioactive isotopes and a large adsorption capacity, which is almost twice that of the other low charge aluminosilicates. In addition, high charge micas are optimum candidates for decontamination of nuclear waste through two different mechanisms; namely an ion exchange reaction and a nonreversible mechanism involving the formation of new stable crystalline phases under hydrothermal conditions. In this work, we report a new in situ optical sensor based on the incorporation of Eu3+ in these high charge micas for tracking the long-term physical-chemical behavior of HLW contaminants in DRG under mild hydrothermal conditions. The incorporation of Eu3+ into the interlayer space of the mica originates a well resolved green and red luminescence, from both the 5D1 and 5D0 excited states, respectively. The formation of new crystalline phases under hydrothermal conditions involves important changes in the Eu3+ emission spectra and lifetime. The most interesting features of Eu3+ luminescence to be used as an optical sensor are (1) the presence or absence of the Eu3+ green emission from the 5D1 excited state, (2) the energy shift of the 5D0 \u2192 7F0 transition, (3) the crystal-field splitting of the 7F1 Eu3+ level, and (4) the observed luminescence lifetimes, which are directly related to the interaction mechanisms between the lanthanide ions and the silicate network<\/p>\n\n\n\n

KeyWords Plus:<\/strong> combined therapy; drug delivery; microtubule dynamics; nanocarrier; nanomaterial.<\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI:<\/strong> 10.18632\/oncotarget.26770<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Eu3+ Luminescence in High Charge Mica: An In Situ Probe for the Encapsulation of Radioactive Waste in Geological Repositories<\/summary>
\n

Author(s):<\/strong> R. Mart\u00edn-Rodr\u00edguez, F. Aguado, M.D. Alba, R. Valiente, and A.C. Perdig\u00f3n<\/p>\n\n\n\n

Source:<\/strong> ACS applied materials & interfaces<\/em><\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 11    P\u00e1ginas:<\/strong> 7559-7565<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

Isolation of high-level radioactive waste (HLW) in deep geological repositories (DGR) through a multibarrier concept is the most accepted approach to ensure long-term safety. Clay minerals are one of the most promising materials to be used as engineered barriers. In particular, high charge micas, as components of the engineered barrier, show superselectivity for some radioactive isotopes and a large adsorption capacity, which is almost twice that of the other low charge aluminosilicates. In addition, high charge micas are optimum candidates for decontamination of nuclear waste through two different mechanisms; namely an ion exchange reaction and a nonreversible mechanism involving the formation of new stable crystalline phases under hydrothermal conditions. In this work, we report a new in situ optical sensor based on the incorporation of Eu3+ in these high charge micas for tracking the long-term physical-chemical behavior of HLW contaminants in DRG under mild hydrothermal conditions. The incorporation of Eu3+ into the interlayer space of the mica originates a well resolved green and red luminescence, from both the 5D1 and 5D0 excited states, respectively. The formation of new crystalline phases under hydrothermal conditions involves important changes in the Eu3+ emission spectra and lifetime. The most interesting features of Eu3+ luminescence to be used as an optical sensor are (1) the presence or absence of the Eu3+ green emission from the 5D1 excited state, (2) the energy shift of the 5D0 \u2192 7F0 transition, (3) the crystal-field splitting of the 7F1 Eu3+ level, and (4) the observed luminescence lifetimes, which are directly related to the interaction mechanisms between the lanthanide ions and the silicate network<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI:<\/strong> <\/a>http:\/\/dx.doi.org\/10.1021\/acsami.8b20030<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Origin of the piezochromism in Cs2CuCl4: Electron-phonon and crystal-structure correlations<\/summary>
\n

Author(s):<\/strong> E. Jara, J. A. Barreda-Arg\u00fceso, J. A. Gonz\u00e1lez, F. Rodr\u00edguez and R. Valiente<\/p>\n\n\n\n

Source:<\/strong> Physical Review B<\/em><\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 13    P\u00e1ginas:<\/strong> 134106 (9 p) <\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

By using optical absorption and Raman spectroscopy, we have investigated the effects of pressure in the
structural, electronic, and vibrational properties of Cs2CuCl4 in the 0\u201320 GPa range. Our study has provided a complete characterization of the electronic and vibrational structures of Cs2CuCl4 in the low-pressure Pnma phase as a function of cell volume and the Cu-Cl bond length, RCu-Cl.We have focused on the electronic structure in the Pnma phase, which is mainly related to the tetrahedral CuCl2\u2212 4 units distorted by the Jahn-Teller effect.
The strong piezochromism of Cs2CuCl4 is caused by the opposite shift of the charge-transfer band gap and the Cu2+ d-d crystal-field transitions with pressure. The high-pressure structure of Cs2CuCl4 above 4.9 GPa yields structural transformations that we ascribe to a change of coordination around Cu2+. The high-pressure phase appears largely amorphized, therefore any structural information from x-ray diffraction is ruled out. Here we use electronic and vibrational probes to get inside the structural information.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: <\/strong>10.1103\/PhysRevB.99.134106<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced spin transition and site-selective metallization in CoCl2<\/summary>
\n

Author(s):<\/strong> J. A. Barreda-Arg\u00fceso, L. Nataf, F. Aguado, I. Hern\u00e1ndez, J. Gonz\u00e1lez, A. Otero-de-la-Roza, V. Lua\u00f1a, Y. Jia, C. Jin, Bongjae Kim, K. Kim, B. I. Min, W. Heribert, A. P. Jephcoat, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Scientific Reports<\/em><\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 9    P\u00e1ginas:<\/strong> 5448 <\/p>\n\n\n\n

Abstract:<\/strong> The interplay between spin states and metallization in compressed CoCl2<\/sub> is investigated by combining diffraction, resistivity and spectroscopy techniques under high-pressure conditions and ab-initio<\/em> calculations. A pressure-induced metallization along with a Co2+<\/sup> high-spin (S\u2009=\u20093\/2) to low-spin (S\u2009=\u20091\/2) crossover transition is observed at high pressure near 70\u2009GPa. This metallization process, which is associated with the p<\/em>–d<\/em> charge-transfer band gap closure, maintains the localization of 3d<\/em> electrons around Co2+<\/sup>, demonstrating that metallization and localized Co2+<\/sup> -3d<\/em> low-spin magnetism can coexist prior to the full 3d<\/em>-electron delocalization (Mott-Hubbard d-d<\/em> breakdown) at pressures greater than 180\u2009GPa.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: <\/strong>https:\/\/doi.org\/10.1038\/s41598-019-41337-4<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

3D Strain in 2D Materials: To What Extent is Monolayer Graphene Graphite?<\/summary>
\n

Author(s):<\/strong> Y. W. Sun, W. Liu, I. Hernandez, J. Gonzalez, F. Rodriguez, D. J. Dunstan, and C. J. Humphreys<\/p>\n\n\n\n

Source:<\/strong> Physical Review Letters<\/em><\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 123    P\u00e1ginas:<\/strong> 135501 <\/p>\n\n\n\n

Abstract:<\/strong> This work addresses a fundamental question: To what extent is graphene graphite? In particular does 2D
graphene have many of the same 3D mechanical properties as graphite, such as the bulk modulus and
elastic constant c33? We have obtained, for the first time, unambiguous Raman spectra from unsupported
monolayer graphene under pressure. We have used these data to quantify the out-of-plane stiffness of
monolayer graphene, which is hard to define due to its 2D nature. Our data indicate a first physically
meaningful out-of-plane stiffness of monolayer graphene, and find it to be consistent with that of graphite.
We also report a shift rate of the in-plane phonon frequency of unsupported monolayer graphene to be
5.4 cm\u22121 GPa\u22121, very close to that of graphite (4.7 cm\u22121 GPa\u22121), contrary to the previous value for
supported graphene. Our results imply that monolayer graphene has similar in-plane and out-of-plane
stiffnesses, and anharmonicities to graphite.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> <\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: <\/strong>10.1103\/PhysRevLett.123.135501<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Monodisperse Gold Nanorods for High-Pressure Refractive Index Sensing<\/summary>
\n

Author(s):<\/strong> C. Mart\u00edn-S\u00e1nchez, G. Gonz\u00e1lez-Rubio, P. Mulvaney, A. Guerrero-Mart\u00ednez, L. M. Liz-Marz\u00e1n, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physical Chemistry Letters<\/em><\/em><\/p>\n\n\n\n

Volume:<\/strong> 10 (7)    P\u00e1ginas:<\/strong> 1587-1593<\/p>\n\n\n\n

Abstract:<\/strong> The effects of hydrostatic pressure on the surface plasmon resonances (SPRs) of aqueous dispersions of monodisperse gold nanorods (AuNRs) were determined up to 9 GPa. The ultranarrow longitudinal SPR band of monodisperse AuNRs allows us to monitor a gradual red shift with pressure, which shows abrupt jumps at the liquid to ice phase VI and ice phase VII transitions. Despite solidifying at low pressure (\u223c1.8 GPa), water displays a regime of quasi-hydrostaticity in said phases VI and VII, up to ca. 5 GPa. Above this pressure, nonhydrostatic effects manifest themselves through broadening of the SPR bands, but barely any effect is observed on the position of the surface plasmon mode. The variation in the SPR peak wavelength with pressure allowed us to determine the pressure dependence of the refractive index of water. Unlike Brillouin scattering or interferometric techniques, this plasmon-spectroscopy-based method leads to a more direct determination of the refractive index, which is well described empirically by Murnaghan-type equations in the three explored phases. We report herein the obtained analytical functions providing the pressure dependence of refractive index in the liquid, ice VI, and ice VII phases of water.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Liquids, optical properties, phisical and chemical process, surface plasmon resonance<\/p>\n\n\n\n

 <\/strong><\/p>\n\n\n\n

DOI: <\/strong>https:\/\/doi.org\/10.1021\/acs.jpclett.9b00636<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Upconversion and Optical Nanothermometry in LaGdO3<\/sub>: Er3+<\/sup> Nanocrystals in the RT-900 K Range dependence of electronic structures <\/summary>
\n

Author(s):<\/strong> V. Guti\u00e9rrez-Cano, F. Rodr\u00edguez, J. A. Gonz\u00e1lez, and R. Valiente<\/p>\n\n\n\n

Source:<\/strong> PapThe Journal of Physical Chemistry C <\/em><\/p>\n\n\n\n

Volume:<\/strong> 123 (49)    P\u00e1ginas:<\/strong> 29818-29828<\/p>\n\n\n\n

Abstract:<\/strong> The search of material hosts being able to incorporate Er3+<\/sup> impurities with a thermally stable structure and high melting temperature is priority in optical thermometry. In this work, we report on the structural and spectroscopic characterization of Er3+<\/sup>\u2013doped and Yb3+<\/sup>\/Er3+<\/sup>\u2013co-doped LaGdO3<\/sub> nanocrystals synthesized via the sol-gel Pechini method. X-ray diffraction (XRD) and Raman spectroscopy unequivocally show that the synthesis method provides nanocrystals with a single-phase B-type monoclinic structure (space group: C2\/m). Intensity decay curves I(t) were measured to investigate the efficiency of upconversion processes yielding green emission. We showed that an energy transfer upconversion (ETU) process involving Yb\u2013Er pairs governs visible emission upon NIR excitation. The temperature dependence of the thermalized green luminescence at 525 nm (2<\/sup>H11\/2\u21924<\/sup>I15\/2<\/sub>) and 549 nm (4<\/sup>S3\/2<\/sub>\u21924<\/sup>I15\/2<\/sub>) was checked for thermometric applications in the RT\u2013900 K temperature range. We demonstrate that the B-type monoclinic phase of LaGdO3<\/sub> is stable from low temperature up to 900 K. Doped with Er3+<\/sup>, it shows suitable thermometer capabilities with a maximum sensitivity of S = 4.3\u00b710\u22123<\/sup> K\u22121<\/sup> at 554 K, and a relative sensitivity decreasing from its maximum value at 0 K to SR<\/sub> = 1.2 \u00b7 10\u22122<\/sup> K\u22121<\/sup> at 298 K. The results suggest that LaGdO3<\/sub> in its B-type monoclinic phase is a promising material as a wide-range temperature sensor, without any further surface protection.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Luminescence, Power, Materials, Lasers, Ions <\/p>\n\n\n\n

 DOI:<\/strong> http:\/\/dx.doi.org\/10.4279\/PIP.110004<\/a><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Structural correlations in Cs2<\/sub>CuCl4<\/sub>: pressure dependence of electronic structures <\/summary>
\n

Author(s):<\/strong> E. Jara, J. A. Barreda-Arg\u00fceso, J.\nGonz\u00e1lez, R. Valiente and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Papers in Physics<\/em> (Focus Series on High\nPressure Semiconductor and Superconductor Physics<\/em>) <\/p>\n\n\n\n

Volume:<\/strong> 11    Issue:<\/strong> 110004  <\/p>\n\n\n\n

Abstract:<\/strong> We have investigated the crystal structure of Cs2CuCl4 in the 0-20 GPa range as a function of pressure and how pressure affects its electronic properties by means of optical absorption spectroscopy. In particular, we focused on the electronic properties in the low-pressure Pnma phase, which are mainly related to the tetrahedral CuClp units distorted by the Jahn-Teller effect. This study provides a complete characterization of the electronic structure of Cs2CuCl4 in the Pmna phase as a function of the cell volume and the Cu-Cl bond length, Rc-u-ci. Interestingly, the opposite shift of the charge-transfer band-gap and the Cu1 4+ d-d crystal-field band shift with pressure are responsible for the strong piezochromism of Cs2CuCl4. We have also explored the high-pressure structure of Cs2CuCl4 above 4.9 GPa yielding structural transformations that are probably associated with a change of coordination around Cu2+. Since the high-pressure phase appears largely amorphized, any structural information from X-ray diffraction is ruled out. We use electronic probes to get structural information of the high-pressure phase.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Cs2CuCl4; electronic structure; high pressure; band gap. <\/p>\n\n\n\n

 DOI:<\/strong> http:\/\/dx.doi.org\/10.4279\/PIP.110004<\/p>\n<\/div><\/details><\/div>\n\n\n\n

The Effects of Hydrostatic Pressure on the Surface Plasmon Resonance of Gold Nanocrystals <\/summary>
\n

Author(s):<\/strong> Camino Mart\u00edn-S\u00e1nchez, J. Antonio Barreda-Arg\u00fceso, Susanne\nSeibt, Paul Mulvaney, and Fernando Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> ACS Nano<\/em> <\/p>\n\n\n\n

Volume:<\/strong> 13<\/strong> (1)    P\u00e1ginas:<\/strong> 498-504  <\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> 10.1021\/acsnano.8b07104<\/p>\n\n\n\n

Abstract:<\/strong> The The\nsurface plasmon resonances of gold nanospheres and nanorods have been measured\nas a function of hydrostatic pressure up to 17 GPa in methanol\u2212 ethanol 4:1\nsolvent and up to 10 GPa in<\/p>\n\n\n\n

paraffi\nn. Both the sphere resonance and the longitudinal rod resonance exhibit\nredshifts, whereas the transverse rod mode shows an extremely weak redshift or\nblueshift depending on the nanorod aspect ratio. Solidifi cation of the solvent\naround 11 GPa causes some aggregation of the particles, readily identifi ed\nthrough broadening of the surface plasmon band and further redshifting. Spectra\ncollected during loading and unloading cycles exhibit only minimal hysteresis\nif the pressure remains below 11 GPa. The surface plasmon shifts are the result\nof two competing eff ects. Compression of the conduction electrons in the\nmetals increases the bulk plasma frequency, which causes a blueshift. However,\nthe increase in the solvent density under hydrostatic load leads to an increase\nin the solvent refractive index, which in turn leads to a redshift. We fi nd\nthat after accounting for the solvent contribution, we can spectroscopically\ndetermine the bulk modulus of the gold nanoparticles with a precision of 10%.\nThe value obtained of K0  = 190 GPa is\nsignifi cantly higher than the value for bulk gold (167 GPa). Furthermore, we\nshow that pressure-induced solidifi cation causes a signifi cant broadening and\nanomalous shift of the surface plasmon band that we attribute to aggregation\nand nanorod deformation. <\/p>\n\n\n\n

KeyWords Plus:<\/strong> Gold nanoparticles, hydrostatic\npressure, surface plasmon resonance, optical absorption, bulk modulus,\nrefractive index<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2018<\/kbd><\/strong><\/p>\n\n\n\n

Thermal degradation of hydrophobic graphite-based thin film nano-coatings observed by Raman spectroscopy<\/summary>
\n

Author(s):<\/strong> Vanessa Guti\u00e9rrez-Cano, Fernando\nRodr\u00edguez, Jes\u00fas A. Gonz\u00e1lez, and Vanesa D\u00edaz<\/p>\n\n\n\n

Source:<\/strong> Thin Solid Films.<\/em><\/p>\n\n\n\n

Volume:<\/strong> 648   <\/strong>P\u00e1ginas:<\/strong> 8\u201311   DOI:<\/strong> doi.org\/10.1016\/j.tsf.2017.12.023 <\/strong><\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

This work reports an alternative method for determining thermal degradation of graphite-based thin film hydrophobic coatings using the D and G graphite vibrations as a probe. We show that the Raman spectrum of the coating as a function of temperature is an efficient probe for detecting changes in the surface properties. Both D and G bands of graphite are sensitive to changes of the coating matrix induced by temperature. We apply the Raman technique to correlate the changes of D and G vibrations with those found by different experimental methods such as contact angle measurements and thermogravimetric analysis to characterize organosilane hydrophobic coatings.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> Raman spectroscopy, Carbon-based materials, Graphite, Thermal degradation, Hydrophobic coatings, Coatings <\/p>\n<\/div><\/details><\/div>\n\n\n\n

A Raman study of the pressure-induced densification of SiO2-based glass-ceramics <\/summary>
\n

Author(s):<\/strong> Silvia Blanco,\nFernando Aguado, Jes\u00fas A. Gonz\u00e1lez, and Fernando Rodriguez<\/p>\n\n\n\n

Source:<\/strong> J. Phys.: Condens. Matter <\/em><\/p>\n\n\n\n

Volume:<\/strong> 30   <\/strong>P\u00e1ginas:<\/strong> 304002 (9pp) DOI:<\/strong> 10.1088\/1361-648X\/aacb1a<\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

Here we report a\nstructural characterization study of glass-ceramics as a function of pressure\nby Raman spectroscopy. We selected a glass-ceramics of Li2<\/sub>O\u2013Al2<\/sub>O3<\/sub>\u2013n<\/em>SiO2<\/sub>\n(n<\/em>\u2009\u2009\u2248\u2009\u20098) doped with ZrO2<\/sub>\nand TiO2<\/sub>. This composition induces slight structural modification in\nSi\u2013O and Si\u2013O\u2013Si bonds in the glass matrix that are crucial to stabilize\nmetastable hexagonal SiO2<\/sub> (\u03b2<\/em>-quartz) solid-solution nano\ncrystals corresponding to \u03b3<\/em>-LiAlSi2<\/sub>O6<\/sub>. This\nstructure yields a more compact \u03b2<\/em>-quartz-type phase that eventually\nstabilizes it in wider pressure range than pure SiO2<\/sub>. Raman\nspectroscopy allows to unravel at least two pressure-induced structural phase\ntransitions at about 6 and 15\u2009GPa that could not be previously revealed by x-ray\ndiffraction. We show that the phase-transition sequence can tentatively be\ndescribed in terms of SiO2<\/sub>-type structure as: \u03b2<\/em>-quartz\u2009\u2009\u2192\u2009\u2009Coesite I\u2009\u2009\u2192\u2009\u2009Coesite II. The measured\ntransition pressures are consistent with the larger cell volume attained in the\n\u03b3<\/em>-LiAlSi2<\/sub>O6<\/sub> yielding a wider metastability\npressure range of the \u03b2<\/em>-quartz-type phase.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-Pressure High-Temperature Stability and Thermal Equation of State of Zircon-Type Erbium Vanadate <\/summary>
\n

Author(s):<\/strong> J. Ruiz-Fuertes, D. Mart\u00ednez-Garc\u00eda, T. Marque\u00f1o, D. Errandonea,\nS. G. MacLeod, T. Bernert, E. Hauss\u00fchl, D. Santamar\u00eda-P\u00e9rez, J. Ib\u00e1\u00f1ez, A.\nMallavarapu, S. N. Achary, C. Popescu, and M. Bettinelli. <\/p>\n\n\n\n

Source:<\/strong> Inorg. Chem.<\/em><\/p>\n\n\n\n

Volume:<\/strong> 57       <\/strong>P\u00e1ginas:<\/strong> 14005<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> 10.1021\/acs.inorgchem.8b01808<\/p>\n\n\n\n

Abstract:<\/strong> The zircon to scheelite phase boundary of ErVO4<\/sub> has been studied by high-pressure and\nhigh-temperature powder and single-crystal X-ray diffraction. This study has\nallowed us to delimit the best synthesis conditions of its scheelite-type\nphase, determine the ambient-temperature equation of state of the zircon and\nscheelite-type structures, and obtain the thermal equation of state of the\nzircon-type polymorph. The results obtained with powder samples indicate that\nzircon-type ErVO4<\/sub> transforms to\nscheelite at 8.2 GPa and 293 K and at 7.5 GPa and 693 K. The analyses yield\nbulk moduli K<\/em>0<\/sub> of 158(13) GPa for\nthe zircon phase and 158(17) GPa for the scheelite phase, with a temperature\nderivative of dK<\/em>0<\/sub>\/dT<\/em> = \u2212[3.8(2)] \u00d7 10\u20133<\/sup> GPa K\u20131<\/sup> and a volumetric thermal expansion of \u03b10<\/sub> = [0.9(2)] \u00d7 10\u20135<\/sup> K\u20131<\/sup> for the zircon phase according to the Berman\nmodel. The results are compared with those of other zircon-type vanadates,\nraising the need for careful experiments with highly crystalline scheelite to\nobtain reliable bulk moduli of this phase. Finally, we have performed\nsingle-crystal diffraction experiments from 110 to 395 K, and the obtained\nvolumetric thermal expansion (\u03b10<\/sub>) for zircon-type ErVO4<\/sub> in the 300\u2013395 K range is [1.4(2)] \u00d7 10\u20135<\/sup> K\u20131<\/sup>, in good agreement with\nprevious data and with our experimental value given from the thermal equation\nof state fit within the limits of uncertainty.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Phase diagram of calcium at high pressure and high temperature <\/summary>
\n

Author(s):<\/strong> S.\nAnzellini, D. Errandonea, S. G. MacLeod, P. Botella, D. Daisenberger, J. M.\nDe\u2019Ath, J. Gonz\u00e1lez-Platas, J. Ib\u00e1\u00f1ez, M. I. McMahon, K. A. Munro, C. Popescu,\nJ. Ruiz-Fuertes, and C. W. Wilson<\/p>\n\n\n\n

Source:<\/strong> Phys. Rev. Materials<\/em><\/p>\n\n\n\n

Volume:<\/strong> 2    P\u00e1ginas:<\/strong> 083608<\/p>\n\n\n\n

DOI:<\/strong> https:\/\/doi.org\/10.1103\/PhysRevMaterials.2.083608<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

Resistively heated diamond-anvil cells have been used together\nwith synchrotron x-ray diffraction to investigate the phase diagram of calcium\nup to 50 GPa and 800 K. The phase boundaries between the Ca-I (fcc), Ca-II\n(bcc), and Ca-III (simple cubic, sc) phases have been determined at these\npressure-temperature conditions, and the ambient temperature equation of state\nhas been generated. The equation of state parameters at ambient temperature\nhave been determined from the experimental compression curve of the observed\nphases by using third-order Birch-Murnaghan and Vinet equations. A thermal\nequation of state was also determined for Ca-I and Ca-II by combining the\nroom-temperature Birch-Murnaghan equation of state with a Berman-type thermal\nexpansion model.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure\/high-temperature phase diagram of zinc <\/summary>
\n

Author(s):<\/strong> D. Errandonea, S. G. MacLeod, J. Ruiz-Fuertes<\/strong>, L. Burakovsky, M. I.\nMcMahon, C. W. Wilson, J. Ib\u00e1\u00f1ez, D. Daisenberger, and C. Popescu<\/p>\n\n\n\n

Source:<\/strong> J. Phys.: Condens. Matter<\/em><\/p>\n\n\n\n

Volume:<\/strong> 30       <\/strong>P\u00e1ginas:<\/strong> 295402<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> 10.1088\/1361-648X\/aacac0<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

The phase diagram of zinc\n(Zn) has been explored up to 140\u2009GPa and 6000\u2009K, by combining optical\nobservations, x-ray diffraction, and ab initio<\/em> calculations. In the\npressure range covered by this study, Zn is found to retain a hexagonal\nclose-packed (hcp) crystal symmetry up to the melting temperature. The known\ndecrease of the axial ratio (c<\/em>\/a<\/em>) of the hcp phase of Zn under\ncompression is observed in x-ray diffraction experiments from 300\u2009K up to the\nmelting temperature. The pressure at which c<\/em>\/a<\/em> reaches  (\u224810\u2009GPa) is slightly affected by\ntemperature. When this axial ratio is reached, we observed that single crystals\nof Zn, formed at high temperature, break into multiple poly-crystals. In\naddition, a noticeable change in the pressure dependence of c<\/em>\/a<\/em>\ntakes place at the same pressure. Both phenomena could be caused by an\nisomorphic second-order phase transition induced by pressure in Zn. The\nreported melt curve extends previous results from 24 to 135\u2009GPa. The pressure\ndependence obtained for the melting temperature is accurately described up to\n135\u2009GPa by using a Simon\u2013Glatzel equation: , where P<\/em> is the pressure in\nGPa. The determined melt curve agrees with previous low-pressure studies and\nwith shock-wave experiments, with a melting temperature of 5060(30) K at\n135\u2009GPa. Finally, a thermal equation of state is reported, which at room-temperature\nagrees with the literature.KeyWords Plus:<\/strong> zinc, x-ray diffraction, ab\ninitio <\/em>calculations, high pressure, high temperature, phase transition,\nmelting \n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Magnetic and electronic properties of the ferroelectric-photovoltaic ordered double perovskite CaMnTi2<\/sub>O6<\/sub> investigated by x-ray absorption spectroscopies<\/em> <\/summary>
\n

Author(s):<\/strong> J.\nHerrero-Mart\u00edn, J. Ruiz-Fuertes, T. Bernert, M. Koch-M\u00fcller, E. Hauss\u00fchl, and\nJ. L. Garc\u00eda-Mu\u00f1oz.<\/p>\n\n\n\n

Source:<\/strong> Phys. Rev. B<\/em> <\/p>\n\n\n\n

Volume:<\/strong> 97    <\/strong>P\u00e1ginas:<\/strong> 235129<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> doi.org\/10.1103\/PhysRevB.97.235129<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

The ferroelectric and\nmagnetic phases of the double perovskite CaMnTi2O6 with A-site\norder have been investigated by soft x-ray absorption and magnetic circular\ndichroism. All spectra point to a very ionic state of divalent Mn and tetravalent\nTi atoms. The effects of the crystal field produced by O ligands around\ntetravalent titanium and the dissimilar Mn1 and Mn2 sites were investigated.\nBoth the so-called square-planar and the octahedrally coordinated Mn sites\nspectroscopically contribute in a rather similar way, with little influence by\nthe oxygen environment. Multiplet calculations suggest a\nsmall O2p\u2212Ti3d charge-transfer component in the FE phase. Magnetic\nsymmetry calculations were performed to determine probable configurations of Mn\nspins compatible with the acentric P42mcstructure and, in combination with\nthe computational magnetic results in Inorg. Chem. 56, 11854 (2017)<\/a>,\nwe have identified the P4\u20322m\u2032c as the\nmost likely magnetic space group keeping invariant the unit cell below TN.\nThis symmetry forces the sign of the magnetic coupling along the Mn columns\nparallel to c to reverse with respect to the coupling between\nneighboring columns. Below TN, the dichroic magnetization loops at\nthe MnL3 edge confirm the absence of spontaneous ferromagnetism,\nalthough a very small field-induced spin polarization was detected in the\nsample.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

An Ultrahigh CO2<\/sub>-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures <\/summary>
\n

Author(s):<\/strong> T.\nMarque\u00f1o, D. Santamar\u00eda-P\u00e9rez, J.\nRuiz-Fuertes<\/strong>, R. Chuli\u00e1-Jord\u00e1n, J. L. Jord\u00e1, F. Rey, C. MaGuire, A. Kavner,\nS. MacLeod, D. Daisenberger, C. Popescu, P. Rodr\u00edguez-Hern\u00e1ndez, and A. Mu\u00f1oz<\/p>\n\n\n\n

Source:<\/strong> Inorg. Chem <\/p>\n\n\n\n

Volume:<\/strong> 57    <\/strong>P\u00e1ginas:<\/strong> 6447<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> 10.1021\/acs.inorgchem.8b00523<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

We report the formation of an ultrahigh CO2<\/sub>-loaded\npure-SiO2<\/sub> silicalite-1 structure at high pressure (0.7\nGPa) from the interaction of empty zeolite and fluid CO2<\/sub> medium. The CO2<\/sub>-filled structure was\ncharacterized in situ<\/em> by means of synchrotron powder X-ray diffraction.\nRietveld refinements and Fourier recycling allowed the location of 16 guest\ncarbon dioxide molecules per unit cell within the straight and sinusoidal\nchannels of the porous framework to be analyzed. The complete filling of pores\nby CO2<\/sub> molecules favors structural stability under\ncompression, avoiding pressure-induced amorphization below 20 GPa, and\nsignificantly reduces the compressibility of the system compared to that of the\nparental empty one. The structure of CO2<\/sub>-loaded silicalite-1 was also\nmonitored at high pressures and temperatures, and its thermal expansivity was\nestimated.<\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Experimental and Theoretical Study of Bi2<\/sub>O2<\/sub>Se Under Compression <\/summary>
\n

Author(s):<\/strong> A. L. J. Pereira, D.\nSantamar\u00eda-P\u00e9rez, J. Ruiz-Fuertes<\/strong>,\nF. J. Manj\u00f3n, V. P. Cuenca-Gotor, R. Vilaplana, O. Gomis, C. Popescu, A. Mu\u00f1oz,\nP. Rodr\u00edguez-Hern\u00e1ndez, A. Segura, L. Gracia, A. Beltr\u00e1n, P. Ruleova, C.\nDrasar, and J. A. Sans<\/p>\n\n\n\n

Source:<\/strong> J. Phys. <\/em>Chem. C<\/em><\/p>\n\n\n\n

Volume:<\/strong> 122  <\/strong>P\u00e1ginas:<\/strong> 8853<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> 10.1021\/acs.jpcc.8b02194<\/p>\n\n\n\n

Abstract:<\/strong> \n\nWe report a joint\nexperimental and theoretical study of the structural, vibrational, elastic,\noptical, and electronic properties of the layered high-mobility semiconductor\nBi2<\/sub>O2<\/sub>Se at\nhigh pressure. A good agreement between experiments and ab initio<\/em>\ncalculations is observed for the equation of state, the pressure coefficients\nof the Raman-active modes and the bandgap of the material. In particular, a\ndetailed description of the vibrational properties is provided. Unlike other\nSill\u00e9n-type compounds which undergo a tetragonal to collapsed tetragonal\npressure-induced phase transition at relatively low pressures, Bi2<\/sub>O2<\/sub>Se\nshows a remarkable structural stability up to 30 GPa; however, our results\nindicate that this compound exhibits considerable electronic changes around 4\nGPa, likely related to the progressive shortening and hardening of the long and\nweak Bi\u2013Se bonds linking the Bi2<\/sub>O2<\/sub> and Se atomic layers. Variations of the\nstructural, vibrational, and electronic properties induced by these electronic\nchanges are discussed. \n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced changes of the structure and properties of monoclinic alpha-chalcocite Cu2<\/sub>S <\/summary>
\n

Author(s):<\/strong> D. Zimmer, J.\nRuiz-Fuertes<\/strong>, W. Morgenroth, A. Friedrich, L. Bayarjargal, E. Hauss\u00fchl, D.\nSantamar\u00eda-P\u00e9rez, S. Frischkorn, V. Milman, and B. Winkler<\/p>\n\n\n\n

Source:<\/strong> Phys. Rev<\/em><\/p>\n\n\n\n

Volume:<\/strong> 97    <\/strong>P\u00e1ginas:<\/strong> 134111<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong>              10.1103\/PhysRevB.97.134111<\/p>\n\n\n\n

Abstract:<\/strong> \n\nThe high-pressure behavior of monoclinic (P21\/c) \u03b1-chalcocite, Cu2S, was\ninvestigated at ambient temperature by single-crystal x-ray diffraction,\nelectrical resistance measurements, and optical absorption spectroscopy up to\n16 GPa. The experiments were complemented by density-functional-theory-based\ncalculations. Single-crystal x-ray diffraction data show that monoclinic\n\u03b1-chalcocite undergoes two pressure-induced first-order phase transitions at \u223c3.1 and \u223c7.1 GPa. The crystal structure of the first high-pressure polymorph,\nHP1, was solved and refined in space group P21\/c with a=10.312(4)\u00c5,\nb=6.737(3)\u00c5, c=7.305(1)\u00c5, and \u03b2=100.17(2)\u2218 at 6.2(3) GPa. The crystal structure of the second high-pressure\npolymorph, HP2, was solved and refined in space group P21\/c with a=6.731(4)\u00c5,\nb=6.689(2)\u00c5, c=6.967(8)\u00c5, and \u03b2=93.18(3)\u2218 at 7.9(4) GPa. Electrical resistance measurements upon compression and\noptical absorption experiments upon decompression show that the structural\nchanges in \u03b1-chalcocite are accompanied by changes of the electrical and\noptical properties. Upon pressure release, the band gap Eg of \u03b1-chalcocite\n(1.24 eV at ambient conditions) widens across the first structural phase\ntransition, going from 1.24 eV at 2.2 GPa (\u03b1-chalcocite) to 1.35 eV at 2.6 GPa\n(HP1), and closes significantly across the second phase transition, going from\n1.32 eV at 4.4 GPa (HP1) to 0.87 eV at 4.9 GPa (HP2). The electrical resistance\nshows similar behavior: its highest value is for the first high-pressure\npolymorph (HP1), and its lowest value is for the second high-pressure polymorph\n(HP2) of \u03b1-chalcocite. These results are interpreted on the basis of calculated\nelectronic band structures.\n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure structural and vibrational properties of monazite-type BiPO4<\/sub>, LaPO4<\/sub>, CePO4<\/sub>, and PrPO4<\/sub> <\/summary>
\n

Author(s):<\/strong> D.\nErrandonea, O. Gomis, P. Rodr\u00edguez-Hern\u00e1ndez, A. Mu\u00f1oz, J. Ruiz-Fuertes<\/strong>, M. Gupta, S. N. Achary, A. Hirsch, F. J. Manj\u00f3n,\nL. Peters, G. Roth, A. K. Tyagi, and M. Bettinelli<\/p>\n\n\n\n

Source:<\/strong> J. Phys.: Condens. Matter<\/em><\/p>\n\n\n\n

Volume:<\/strong> 30    <\/strong>P\u00e1ginas: <\/strong>065401<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> doi.org\/10.1088\/1361-648X\/aaa20d<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

Monazite-type BiPO4<\/sub>, LaPO4, and PrPO4 have been\nstudied under high pressure by
\nab initio <\/em>simulations and Raman spectroscopy measurements in the\npressure range of stability of the monazite structure. A good agreement between\nexperimental and theoretical Raman- active mode frequencies and pressure\ncoefficients has been found which has allowed us to discuss the nature of the\nRaman-active modes. Besides, calculations have provided us with information on\nhow the crystal structure is modified by pressure. This information has allowed\nus to determine the equation of state and the isothermal compressibility tensor\nof the four studied compounds. In addition, the information obtained on the\npolyhedral compressibility has been used to explain the anisotropic axial\ncompressibility and the bulk compressibility of monazite phosphates. Finally,\nwe have carried out a systematic discussion on the high-pressure behavior of\nthe four studied phosphates in comparison to results of previous studies. <\/p>\n\n\n\n

Keywords:<\/strong> monazite, orthophosphate,\nhigh pressure, equation of state, Raman, Ab initio <\/em>calculations <\/p>\n<\/div><\/details><\/div>\n\n\n\n

A Brief Review of the Effects of Pressure on Wolframite-Type Oxides <\/summary>
\n

Author(s):<\/strong> D.\nErrandonea and J. Ruiz-Fuertes <\/strong><\/p>\n\n\n\n

Source:<\/strong> Crystals<\/em><\/p>\n\n\n\n

Volume:<\/strong> 8      <\/strong>P\u00e1ginas: <\/strong>71<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> doi.org\/10.3390\/cryst8020071<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

In\nthis article we review the advances that have been made on the understanding of\nthe high-pressure structural, vibrational, and electronic properties of\nwolframite-type oxides since the first works in the early 1990s. Mainly\ntungstates, which are the best known wolframites, but also tantalates and\nniobates, with an isomorphic ambientpressure wolframite structure, have been\nincluded in this review. Apart from estimating the bulk moduli of all known\nwolframites; the cation-oxygen bond distances and their change with pressure\nhave been correlated with their compressibility. The composition variations of\nall wolframites have been employed to understand their different structural\nphase transitions to post-wolframite structures as a response to high pressure.\nThe number of Raman modes and band gap energy changes have been also analyzed\nin the basis of these compositional differences. The reviewed results are\nrelevant for both fundamental science and for the development of wolframites as\nscintillating detectors. The possible next research venues of wolframites have\nalso been evaluated.Keywords:<\/strong> wolframite,\nhigh-pressure, phase transitions, crystal structure, phonons, band structure. \n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Bandgap behavior and singularity of the domain-induced light scattering through the pressure-induced ferroelectric transition in relaxor ferroelectric AxBa1-x<\/sub>Nb2<\/sub>O6<\/sub> (A: Sr,Ca) <\/summary>
\n

Author(s):<\/strong> J. Ruiz-Fuertes, O. Gomis, A. Segura, M. Bettinelli,\nM. Burianek, and M. M\u00fchlberg<\/strong><\/p>\n\n\n\n

Source:<\/strong> Appl. Phys. Lett<\/em><\/p>\n\n\n\n

Volume:<\/strong> 112  <\/strong>P\u00e1ginas: <\/strong>042901<\/p>\n\n\n\n

 <\/strong>DOI:<\/strong> https:\/\/doi.org\/10.1063\/1.5012111<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

In this letter, we have investigated the electronic\nstructure of Ax<\/em>Ba1\u2013x<\/em>Nb2O6 relaxor ferroelectrics on the basis of\noptical absorption spectroscopy in unpoled single crystals with A<\/em>\u2009<\/em>=\u2009<\/em>Sr\nand Ca under high pressure. The direct character of the fundamental transition\ncould be established by fitting Urbach’s rule to the photon energy dependence\nof the absorption edge yielding bandgaps of 3.44(1) eV and 3.57(1) eV for A<\/em>\u2009<\/em>=\u2009<\/em>Sr\nand Ca, respectively. The light scattering by ferroelectric domains in the\npre-edge spectral range has been studied as a function of composition and\npressure. After confirming with x-ray diffraction the occurrence of the\npreviously observed ferroelectric to paraelelectric phase transition at 4\u2009GPa,\nthe light scattering produced by micro- and nano-ferroelectric domains at 3.3\u2009eV\nin Ca0.28Ba0.72Nb2O6 has been probed. The direct bandgap remains virtually\nconstant under compression with a drop of only 0.01\u2009eV around\nthe phase transition. Interestingly, we have also found that light scattering\nby the polar nanoregions in the paraelectric phase is comparable to the\ndispersion due to ferroelectric microdomains in the ferroelectric state.\nFinally, we have obtained that the bulk modulus of the ferroelectric phase of\nCa0.28Ba0.72Nb2O6 is B<\/em>0\u2009=\u2009222(9)\nGPa.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2017<\/strong><\/p>\n\n\n\n

Structural refinement, photoluminescence and Raman spectroscopy of Wurtzite Mn-doped ZnO pellets <\/summary>
\n

Author(s):<\/strong> J. Marquina, J.\nMart\u00edn, J. Luengo, F. Vera, L. Roa, G.E. Delgado, F. Rodr\u00edguez, C.\nRenero-Lecuna, R. Valiente, and J. Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong> Revista Mexicana de F\u00edsica<\/em><\/p>\n\n\n\n

Volume:<\/strong> 63<\/strong> (1)   <\/strong>P\u00e1ginas:<\/strong> 32-39 \n<\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

We report the\nresults of the Rietveld refinement, photoluminescence and Raman spectroscopy of\nMn-doped ZnO ceramic pellets. Rietveld refinement shows that samples\ncrystallize in the wurtzite structure and for the Mn-doped sample indicates\nthat the Mn atoms substitute the Zn tetrahedral crystallographic sites in the\nZnO host lattice. The emission and absorption spectra of Mn-doped ZnO have been\ninvestigated in the Visible-UV region and the data have been interpreted in terms\nof the wurtzite ZnO electronic structure. Two broad bands, one due to\nsuperposition between donor bound excitons (DX) and free excitons (FX) and\nother due free-to-bond excitonic recombination (FB) dominates the\nlow-temperature photoluminescence spectra of Mn-doped ZnO bulk. In the Raman\nspectrum, an extra mode at 520 cm-1 has been observed in agreement with earlier\nworks, and it is an indicator for the incorporation of Mn+2 ions into the ZnO\nhost matrix since it is not is observed in ZnO pristine.<\/p>\n\n\n\n

Keywords:<\/strong>\nDMS; Photoluminescence; Raman spectroscopy; ZnO <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Can the d<\/em>-Orbital Splitting Unveil the Local Structure of Cu2+<\/sup> Ions? Study on the K2<\/sub>ZnF4<\/sub>: Cu2+<\/sup> Archetype <\/summary>
\n

Author(s):<\/strong> F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Cap. del libro Correlations in\nCondensed Matter under Extreme Conditions<\/em>, Ed. Springer International\nPublishing<\/p>\n\n\n\n

P\u00e1ginas:<\/strong> 3-15 <\/p>\n\n\n\n

Abstract: <\/strong>\n\nJahn-Teller\n(JT) transition-metal ions like Cu\\(^{2+}\\) (\\(d^9\\)) or Mn\\(^{3+}\\) (\\(d^4\\))\nin octahedral coordination exhibit larger distortions than non-JT ions like\nMn\\(^{2+}\\) or Fe\\(^{3+}\\) (both \\(d^5\\)) in oxides and halides with perovskite\ntype structure. Their mutual interactions eventually determine the type of\ndistortion and the way they couple each other, being at the core of some\nrelevant physical properties. When a JT ion is introduced as an impurity in an\noctahedral or nearly octahedral site, it provokes a low-symmetry lattice\ndistortion as a consequence of the instability associated with the electronic\nground state degeneracy, \\(e_g (x^2 -y^2, 3z^2 -r^2 )\\). The distortion degree,\n\\(\\rho \\), depends mainly on the electron-ion coupling interaction related to\nthe \\(E\\otimes e\\) JT effect, and it is modulated by the host crystal\nstructure. This scenario explains for example why Cu\\(^{2+}\\) induces a large\ndistortion of the CuF\\(_6\\) octahedron, when Cu\\(^{2+}\\) replaces Zn\\(^{2+}\\)\neither in the perovskite KZnF\\(_3\\) or in the layered perovskite\nK\\(_2\\)ZnF\\(_4\\). However, there is a long debate about whether the splitting,\n\\(\\varDelta _e\\) of the \\(O_h\\) \\(e_g (x^2 -y^2, 3z^2 -r^2 )\\) orbitals into\n\\(a_{1g}\\) and \\(b_{1g}\\) is proportional to \\(\\rho \\) or \\(\\varDelta _e\\)\ncontains additional contributions from the rest-of-the-lattice (crystal\nanisotropy) aside \\(\\rho \\). Elucidation of this controversy is important in\norder to establish structural correlations between \\(\\varDelta _e\\) and \\(\\rho\n\\), for an eventual local structure determination of JT impurities from optical\nspectroscopy. Recent studies on K\\(_2\\)ZnF\\(_4\\):Cu\\(^{2+}\\) report different\nviews of this problem. Here we show that \\(\\varDelta _e\\) scales linearly with\n\\(\\rho \\). High pressure experiments and JT-ion compound series of different\ndimensionality give support for the proposed scenario and provide structural\ncorrelations relating \\(\\rho \\) and \\(\\varDelta _e\\) in Cu\\(^{2+}\\) and\nMn\\(^{3+}\\) systems.\n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Volume and pressure dependences of the electronic, vibrational, and crystal structures of Cs2<\/sub>CoCl4<\/sub>: Identification of a pressure-induced piezochromic phase at high pressure <\/summary>
\n

Author(s):<\/strong> L. Nataf, F.\nAguado, I. Hern\u00e1ndez, R. Valiente, J. Gonz\u00e1lez, M.N. Sanz-Ortiz,  H.\nWilhelm, A.P. Jephcoat, F. Baudelet, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Physical Review B<\/em><\/p>\n\n\n\n

Volume:<\/strong> 95<\/strong> (1)   <\/strong>P\u00e1ginas:<\/strong> 014110<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.95.014110 <\/p>\n\n\n\n

Abstract: <\/strong>\n\nThis work investigates the\nhigh-pressure structure of Cs2CoCl4 and how it affects the electronic and\nvibrational properties using optical absorption, Raman spectroscopy, x-ray\ndiffraction, and x-ray absorption in the 0\u201315 GPa range. In particular, we\nfocus on the electronic and local structures of Co2+ , since compression of Cs2\nCoCl4 yields structural transformations associated with change of coordination\naround Co2+, which are eventually responsible for the intense piezochromism at\n7 GPa. This study provides a complete characterization of the electronic and\nvibrational structures of Cs2CoCl4 in the Pnma phase as a function of the cell\nvolume and the local CoCl4 bond length, RCo-Cl, as well as its corresponding\nequation of state. In addition, our interest is to elucidate whether the phase\ntransition undergone by Cs2CoCl4 at 7 GPa leads to a perovskite-layer-type\nstructure where Co2+ is sixfold coordinated, decomposes into CsCl + CsCoCl3 ,\nor it involves an unknown phase with different coordination sites for Co2+. We\nshow that Co2+ is sixfold coordinated in the high-pressure phase. The analysis\nof optical spectra and x-ray diffraction data suggests the formation of an\ninterconnected structure of exchange-coupled Co2+ through edge-sharing\noctahedra at high pressure. \n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Unveiling the Local Structure of Cu2+ Ions from d-Orbital Splitting. Application to K2<\/sub>ZnF4<\/sub>: Cu2+<\/sup> and KZnF3<\/sub>: Cu2+<\/sup> <\/summary>
\n

Author(s):<\/strong> F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Inorganic Chemistry<\/em><\/p>\n\n\n\n

Volume:<\/strong> 56<\/strong> (4)   <\/strong>P\u00e1ginas:<\/strong> 2019-2036<\/p>\n\n\n\n

DOI:<\/em><\/strong> 10.1021\/acs.inorgchem.6b02677<\/em><\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

An<\/sub><\/em>MXm<\/sub><\/em> perovskites with Jahn\u2212Teller M ions exhibit an\nample variety of physical phenomena. The local structure of MX6<\/sub> octahedra and the way they couple with each\nother are at the core of their properties. Correlations between structure and\nd-orbital electronic splitting in Cu2+<\/sup> and Mn3+<\/sup> show that MX6<\/sub> distortions scale linearly with the splitting\n\u0394e<\/sub> of eg<\/sub>(x<\/em>2<\/sup> \u2212 y<\/em>2<\/sup>, 3z<\/em>2<\/sup> \u2212 r<\/em>2<\/sup>) orbitals. We apply such\ncorrelations to determine the low-symmetry distortion of Cu2+<\/sup> impurities in KZnF3<\/sub> and K2<\/sub>ZnF4<\/sub> by optical spectroscopy.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Highly efficient photoluminescence from isolated Eu3+<\/sup> ions embedded in high-charge mica <\/summary>
\n

Author(s):<\/strong> R.\nMart\u00edn-Rodr\u00edguez, R. Valiente, F. Aguado, and A.C. Perdig\u00f3n<\/p>\n\n\n\n

Source:<\/strong> Journal of Materials\nChemistry C<\/em><\/p>\n\n\n\n

Volume:<\/strong> 5<\/strong> (39)   <\/strong>P\u00e1ginas:<\/strong> 10360-10368<\/p>\n\n\n\n

DOI:<\/em><\/strong> 10.1021\/acs.inorgchem.6b02677<\/em><\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

An<\/sub><\/em>MXm<\/sub><\/em> perovskites with Jahn\u2212Teller M ions exhibit an\nample variety of physical phenomena. The local structure of MX6<\/sub> octahedra and the way they couple with each\nother are at the core of their properties. Correlations between structure and\nd-orbital electronic splitting in Cu2+<\/sup> and Mn3+<\/sup> show that MX6<\/sub> distortions scale linearly with the splitting\n\u0394e<\/sub> of eg<\/sub>(x<\/em>2<\/sup> \u2212 y<\/em>2<\/sup>, 3z<\/em>2<\/sup> \u2212 r<\/em>2<\/sup>) orbitals. We apply such\ncorrelations to determine the low-symmetry distortion of Cu2+<\/sup> impurities in KZnF3<\/sub> and K2<\/sub>ZnF4<\/sub> by optical spectroscopy.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Phase transition sequences in tetramethylammonium tetrachlorometallates by X-ray diffraction and spectroscopic measurements <\/summary>
\n

Author(s):<\/strong> Jack Binns, Garry J McIntyre, Jos\u00e9 A\nBarreda-Arg\u00fceso, Jes\u00fas Gonz\u00e1lez, Fernando Aguado, Fernando Rodr\u00edguez, Rafael Valiente,\nand Simon Parsons<\/p>\n\n\n\n

Source:<\/strong> Acta Crystallographica\nSection B: Structural Science, Crystal Engineering and Materials<\/em><\/p>\n\n\n\n

Volume:<\/strong> 73 P\u00e1ginas:<\/strong> 844-855<\/p>\n\n\n\n

DOI:<\/em><\/strong> <\/em>10.1107\/S2052520617006412<\/em><\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

<\/p>\n\n\n\n

The phase transition sequences of two members of the tetramethylammonium tetrachlorometallate(III) family of hybrid organic-inorganic salts have been determined and structurally characterized as a function of temperature for the first time. Unusually, a reduction in point-group symmetry with increasing temperature until reaching a cubic prototype phase is observed. Two additional intermediate phases are observed for Fe3+. First-principles calculations and the presence of short Cl…Cl contacts for Ga3+ suggest the [GaCl4]- anion to be conformationally hindered due to stronger lone-pair-\u03c3-hole interactions. The conformationally more flexible Fe3+ structures show sublattice melting with the onset of rotational disorder in the [NMe4]+ cations occurring 40\u2005K below the corresponding onset of rotational disorder in the [FeCl4]- sublattice.<\/p>\n\n\n\n

KEYWORDS: <\/strong>crystal packing; intermolecular interactions; phase transitions <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Volume and bond length dependences of the electronic structure of 6-fold and 8-fold coordinated Co2+<\/sup> in pressure transformed CoF2<\/sub> <\/summary>
\n

Author(s):<\/strong> J.A. Barreda-Arg\u00fceso, F. Aguado, J. Gonz\u00e1lez, R.\nValiente, L. Nataf, M.N. Sanz-Ortiz, and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Journal of Physics:\nConference Series<\/em> <\/p>\n\n\n\n

Volume:<\/strong> 950 P\u00e1ginas:<\/strong> 042016<\/p>\n\n\n\n

DOI:<\/em><\/strong>  <\/em>10.1088\/1742-6596\/950\/4\/042016\n<\/p>\n\n\n\n

Abstract: <\/strong>\n\nThis work reports an optical absorption study on CoF2<\/sub> under\nhigh-pressure conditions in the 0-80 GPa range. A recent structural study1\nperformed on the pressure-induced phase-transition sequence of CoF2<\/sub>\nreveals that this compound undergoes a structural transformation associated\nwith a change of Co2+<\/sup> coordination from 6 (rutile type) to 8\n(fluorite type) at 15 GPa, what implies a profound change in the Co2+<\/sup>\nelectronic ground state associated with the inversion of d<\/em> orbitals from\n(t<\/em>2g<\/sub> 5 e<\/em> g<\/sub> 2) to (e<\/em>g<\/sub> 4t<\/em>2g<\/sub>\n3). This allows us to explore the Co2+<\/sup> electronic structure, and\nhence 10Dq<\/em>, as a function of the density and the Co-F bond length in\nboth CoF6<\/sub> (rutile phase) and CoF8<\/sub> (fluorite phase)\ncoordinations. The results are compared with those obtained in KCoF3<\/sub>\n(perovskite) in a wide range of Co-F distances (from 2.04 to 1.83 \u00c5).\n\n\n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Sensitization, energy transfer and infra-red emission decay modulation in Yb3+<\/sup>-doped NaYF4<\/sub>\u00a0nanoparticles with visible light through a perfluoroanthraquinone chromophore <\/summary>
\n

Author(s):<\/strong> H. Lu, Y. Peng, H. Ye, X. Cui, J. Hu, H. Gu, A. N.\nKhlobystov, M. A. Green, P.J. Blower, P.B. Wyatt, W.P. Gillin and I. Hern\u00e1ndez<\/p>\n\n\n\n

Source:<\/strong> Scientific Reports <\/em> <\/em><\/p>\n\n\n\n

Volume:<\/strong> 7 P\u00e1ginas:<\/strong> 5066<\/em><\/p>\n\n\n\n

DOI:<\/em><\/strong>  <\/em>doi.org\/10.1038\/s41598-017-05350-9<\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

Infra-red emission (980\u2009nm) of sub 10\u2009nm Yb3+-doped NaYF4 nanoparticles has been\nsensitized through the excitation of 2-hydroxyperfluoroanthraquinone\nchromophore (1,2,3,4,5,6,7-heptafluro-8-hydroxyanthracene-9,10-dione)\nfunctionalizing the nanoparticle surface. The sensitization is achieved with a\nbroad range of visible light excitation (400\u2013600\u2009nm). The overall near infra-red (NIR)\nemission intensity of Yb3+ ions is increased by a factor 300 as a result of the\nbroad and strong absorption of the chromophore compared with ytterbium\u2019s\nintrinsic absorption. Besides the Yb3+ NIR emission, the hybrid composite shows\norganic chromophore-based visible emission in the orange-red region of the\nspectrum. We observe the energy migration process from the sensitized Yb3+ ions\nat the surface to those in the core of the particle using time-resolved optical\nspectroscopy. This highlights that the local environments for emitting Yb3+\nions at the surface and center of the nanoparticle are not identical, which\ncauses important differences in the NIR emission dynamics. Based on the\nunderstanding of these processes, we suggest a simple strategy to control and\nmodulate the decay time of the functionalized Yb3+-doped nanoparticles over a\nrelatively large range by changing physical or chemical parameters in this\nmodel system.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Structural refinement, photoluminescence and Raman spectroscopy of Wurtzite Mn-doped ZnO pellets <\/summary>
\n

Author(s):<\/strong> J. Marquina, J. Mart\u00edn, J. Luengo, F. Vera, L.\nRoa, G.E. Delgado, F. Rodr\u00edguez, C. Renero-Lecuna, R. Valiente and J. Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong> Revista Mexicana de F\u00edsica<\/em> <\/p>\n\n\n\n

Volume:<\/strong> 63 P\u00e1ginas:<\/strong> 32-39<\/em><\/p>\n\n\n\n

ISSN 0035-001X<\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

We report the results of the Rietveld refinement,\nphotoluminescence and Raman spectroscopy of Mn-doped ZnO ceramic pellets.\nRietveld refinement shows that samples crystallize in the wurtzite structure\nand for the Mn-doped sample indicates that the Mn atoms substitute the Zn\ntetrahedral crystallographic sites in the ZnO host lattice. The emission and\nabsorption spectra of Mn-doped ZnO have been investigated in the Visible-UV\nregion and the data have been interpreted in terms of the wurtzite ZnO\nelectronic structure. Two broad bands, one due to superposition between donor\nbound excitons (DX) and free excitons (FX) and other due free-to-bond excitonic\nrecombination (FB) dominates the low-temperature photoluminescence spectra of\nMn-doped ZnO bulk. In the Raman spectrum, an extra mode at \u223c520 cm-1\nhas been observed in agreement with earlier works, and it is an indicator for\nthe incorporation of Mn+2 ions into the ZnO host matrix since it is not is\nobserved in ZnO pristine.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Highly efficient photoluminescence from isolated Eu3+ ions embedded in high-charge mica <\/summary>
\n

Author(s):<\/strong> R Mart\u00edn-Rodr\u00edguez, R Valiente, F Aguado, AC Perdig\u00f3n<\/p>\n\n\n\n

Source:<\/strong>\nJournal of\nMaterials Chemistry C<\/em><\/p>\n\n\n\n

Volume:<\/strong>\n5 P\u00e1ginas:<\/strong> 10360-10368<\/p>\n\n\n\n

DOI:<\/strong>10.1039\/C7TC01818E<\/p>\n\n\n\n

Abstract: <\/strong><\/p>\n\n\n\n

Incorporation of lanthanide ions in synthetic clay minerals\nis a promising approach to combine the efficient sharp-line emission of\nlanthanides with the unique structural stability and high adsorption capacity\nof high-charge micas. These aluminosilicate hosts are synthetic exchanger\nlayered-clays which have demonstrated a unique selectivity in heavy metal and\nradionuclide capture. A phosphor based on the emission of Eu3+ ions\nhomogeneously distributed in the dispersing inorganic-host high-charge mica\nNa2[Mg6]VIII[Si6Al2]IVO20F4 is reported. Eu3+ cations act as an ideal\nluminescent probe to study the physical\u2013chemical adsorption mechanisms of the\ncontaminants in the aluminosilicate. Despite the forbidden nature of the f\u2013f\ntransition involved, well-resolved Eu3+ luminescence is observed from both the\n5D0 and the 5D1 Eu3+ states in the high-charge mica, and, in contrast to\nprevious results, the use of an antenna for light absorption and transfer to\nthe lanthanide is not required. The fluorinated nature and the absence of iron\nimpurities, together with the homogeneous dispersion of lanthanide ions\nprovided by Al3+, makes the high-charge mica a biocompatible host as an optical\nsensor or drug delivery material. Further evidence of the homogeneous\ndistribution and isolation of Eu3+ cations in the hexagonal cavities of the\nmica is provided by spectroscopic luminescence and lifetime measurements.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2016<\/strong><\/p>\n\n\n\n

A study of Ce3+<\/sup> to Mn2+<\/sup> energy transfer in high transmission glasses using time-resolved spectroscopy<\/summary>
\n

Author<\/strong>(s): <\/strong>Susana G\u00f3mez-Salces, Jose Antonio Barreda-Arg\u00fceso,\nRafael Valiente, Fernando Rodr\u00edguez<\/p>\n\n\n\n

Publication date: <\/strong>2016<\/p>\n\n\n\n

Source:<\/strong> Journal of Materials Chemistry C                       Volumen:<\/strong>  4 Issue:<\/strong>            38       Pag.:<\/strong> 9021-9026<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/C6TC01408A<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

This work investigates the energy transfer from Ce3+<\/sup> to Mn2+<\/sup>\nin high transmission glass (HTG) doped with CeO2<\/sub> and MnO through time-resolved spectroscopy\nto transform the solar spectrum into a more efficient red-enhanced spectrum for traditional Si-based solar cells. We show that both\nMn3+<\/sup> and Mn2+<\/sup> and Ce3+<\/sup> and Ce4+<\/sup>\ncentres are formed in HTG through\ntheir absorption and emission\/excitation spectra. Interestingly, Ce3+\n<\/sup>excitation at 320 nm yields both Ce3+<\/sup> (400 nm) and Mn2+<\/sup> (530 nm) emissions for doping concentrations of 0.1\u20131% Ce3+<\/sup> and 0.1% Mn2+<\/sup>.\nThe energy transfer process in HTG is noteworthy since it enhances the\ncapability for blue-to-red light transformation, which is important for\na concentrator in photovoltaic\napplications. This work analyses the\nnon-radiative vs.<\/em> radiative\nCe3+<\/sup> \u2192 Mn2+<\/sup> energy\ntransfer process in this optically enriched HTG. In the explored doping range we show that\nenergy transfer is purely radiative<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Carbon implanted waveguides in soda lime glass doped with Yb 3+<\/sup> and Er 3+<\/sup> for visible light emission<\/summary>
\n

Author<\/strong>(s): <\/strong>GV. V\u00e1zquez, R. Valiente, S. G\u00f3mez-Salces,\nE. Flores-Romero, J. Rickards, R. Trejo-Luna<\/p>\n\n\n\n

Publication date: <\/strong>2016\/5\/31<\/p>\n\n\n\n

Source:<\/strong> Optics & Laser Technology                 Volumen:<\/strong>  79   Issue<\/strong>:<\/strong> 8     Pag<\/strong>.<\/strong>:<\/strong> 132<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.optlastec.2015.12.002<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

Channel waveguides were fabricated by carbon\nimplantation in soda lime glass\nsamples doped with Er 3+<\/sup> and Yb 3+<\/sup>, exhibiting good confinement and both monomode and multimode behaviour at 633 nm. Excitation at near infrared (NIR) and ultraviolet\n(UV) spectral ranges were used in order\nto obtain anti-Stokes (upconversion) and Stokes (downshift)\nemission in the visible range, respectively. The characteristic green and red bands of Er 3+<\/sup>\ntransitions were observed, showing the potential of Yb 3+<\/sup>\nand Er 3+<\/sup> co- …<\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Crystal-Field Theory Validity Through Local (and Bulk) Compressibilities in CoF2<\/sub> and KCoF3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>J Antonio Barreda-Arg\u00fceso,\nFernando Aguado, Jes\u00fas Gonz\u00e1lez, Rafael Valiente, Lucie\nNataf, Marta N Sanz-Ortiz, Fernando Rodr\u00edguez<\/p>\n\n\n\n

Publication<\/strong>\ndate: <\/strong>2016\/8\/17<\/p>\n\n\n\n

Source:<\/strong>  Journal of physical chemistry. C       Volumen:<\/strong>  120   Issue<\/strong>:<\/strong> 33            Pag<\/strong>.<\/strong>:<\/strong> 18788<\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/acs.jpcc.6b06132<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

Crystal field theory (CFT) predicts that crystal field acting on an transition-metal (TM) ion complex of cubic symmetry varies as R<\/em>\u20135<\/sup>, where R<\/em> is the TM-ligand distance. Yet simple and old-fashioned, CFT is used extensively since it provides excellent results in most TM ion-bearing systems, although no direct and thorough validation has been provided so far. Here we investigate the evolution of the electronic and crystal structures of two archetypal Co2+<\/sup> compounds by optical absorption and X-ray diffraction under high pressure. Both the electronic excited states and crystal-field splitting, \u0394 = 10Dq<\/em>, between 3d<\/em>(e<\/em>g<\/sub> + t<\/em>2g<\/sub>) orbitals of Co2+<\/sup> as a function of volume, V<\/em>, and Co\u2013F bond length, R<\/em>, in 6-fold octahedral (oct) and 8-fold hexahedral (cub) coordination in compressed CoF2<\/sub> have been analyzed. We demonstrated that \u0394 scales with R<\/em> in both coordinations as R<\/em>\u2013n<\/em><\/sup>, with n<\/em> close to 5 in agreement with CFT predictions. The pressure-induced rutile to fluorite structural phase transition at 15 GPa in CoF2<\/sub> is associated with an increase of R<\/em> due to the 6 \u2192 8 coordination change. The experimental \u0394(oct)\/ \u0394(cub) = \u22121.10 for the same R<\/em>-values is close to \u22129\/8, in agreement with CFT. A similar R<\/em>-dependence is observed in KCoF3<\/sub> in which the CoF6<\/sub>O<\/em>h<\/sub> coordination is maintained in the 0\u201380 GPa pressure range.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Modeling blue to UV upconversion in \u03b2-NaYF4<\/sub>: Tm3+<\/sup><\/summary>
\n

Author<\/strong>(s): <\/strong>Pedro Villanueva-Delgado, Karl W Kr\u00e4mer, Rafael Valiente, Mathijs\nde Jong, Andries Meijerink<\/p>\n\n\n\n

Publication date: <\/strong>2016<\/p>\n\n\n\n

Source:<\/strong> Physical Chemistry Chemical\nPhysics                     Volumen:<\/strong>  18           Issue<\/strong>:<\/strong>            39       Pag<\/strong>.<\/strong>:<\/strong> 27396-27404<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/C6CP04347J<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

Samples of 0.01% and 0.3% Tm3+<\/sup>-doped \u03b2-NaYF4<\/sub> show upconverted\nUV luminescence at 27660 cm\u22121<\/sup> (361 nm) after blue\nexcitation at 21140 cm\u22121<\/sup> (473 nm). Contradictory upconversion mechanisms in the literature are reviewed and two of them are investigated in detail. Their agreement\nwith emission and two-color excitation experiments is examined and compared. Decay curves are analyzed using the Inokuti\u2013Hirayama model, an average rate\nequation model, and a microscopic rate equation model that includes the\ncorrect extent of energy transfer. Energy migration is found\nto be negligible in these samples, and hence the average\nrate equation model fails to\ncorrectly describe the decay curves. The microscopic rate equation model accurately fits the experimental data and reveals\nthe strength and multipolarity of various interactions. This microscopic model is able to\ndetermine the most likely upconversion mechanism.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Multiwalled Carbon Nanotubes Inhibit Tumor Progression in a Mouse Model<\/summary>
\n

Author<\/strong>(s): <\/strong>Lorena Garc\u00eda\u2010Hevia, Juan C\nVillegas, Fidel Fern\u00e1ndez, \u00cd\u00f1igo Casafont, Jes\u00fas\nGonz\u00e1lez, Rafael Valiente, M\u00f3nica L Fanarraga<\/p>\n\n\n\n

Publication date: <\/strong>2016\/2\/1<\/p>\n\n\n\n

Source:<\/strong> Advanced healthcare materials          Volumen:<\/strong>  5 Pag<\/strong>.<\/strong>:<\/strong> 1080<\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/adhm.201500753<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

Understanding the molecular mechanisms underlying the biosynthetic interactions between particular nanomaterials with specific cells\nor proteins opens new alternatives in nanomedicine and nanotoxicology. Multiwalled carbon nanotubes (MWCNTs) have long\nbeen explored as drug delivery systems\nand nanomedicines against cancer. There are high expectations for their use in therapy and diagnosis. These filaments can translocate inside cultured cells and intermingle with the protein\nnanofilaments of the cytoskeleton, interfering with the biomechanics\nof cell division mimicking the effect\nof traditional microtubule-binding\nanti-cancer drugs such as paclitaxel. Here, it is\nshown how MWCNTs can trigger significant anti-tumoral effects\nin vivo, in solid malignant\nmelanomas produced by allograft transplantation. Interestingly, the MWCNT\nanti-tumoral effects are maintained\neven in solid melanomas generated from paclitaxel-resistant cells. These findings provide great expectation\nin the development of groundbreaking adjuvant synthetic microtubule-stabilizing\nchemotherapies to overcome drug resistance\nin cancer.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Nano-ZnO leads to tubulin macrotube assembly and actin bundling, triggering cytoskeletal catastrophe and cell necrosis<\/summary>
\n

Author<\/strong>(s): <\/strong>Lorena Garc\u00eda-Hevia, Rafael Valiente, Rosa\nMart\u00edn-Rodr\u00edguez, Carlos Renero-Lecuna, Jes\u00fas\nGonz\u00e1lez, Lidia Rodr\u00edguez-Fern\u00e1ndez, Fernando Aguado, Juan C Villegas, M\u00f3nica L\nFanarraga<\/p>\n\n\n\n

Publication date: <\/strong>25 Apr\n2016<\/p>\n\n\n\n

Source:<\/strong> Nanoscale                       Volumen:<\/strong>  8 Issue<\/strong>:<\/strong>            21       Pag<\/strong>.<\/strong>:<\/strong> 10963-10973<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/C6NR00391E<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

Zinc is a crucial element in biology that plays chief\ncatalytic, structural and protein regulatory roles. Excess cytoplasmic zinc is toxic to\ncells so there are cell-entry and intracellular buffering mechanisms that control intracellular zinc availability. Tubulin and actin are two zinc-scavenging proteins that are essential components of the cellular cytoskeleton implicated in cell division, migration and cellular architecture maintenance. Here we demonstrate how exposure to\ndifferent ZnO nanostructures, namely ZnO commercial nanoparticles and custom-made ZnO nanowires, produce acute cytotoxic effects in human keratinocytes (HaCat) and epithelial cells (HeLa) triggering\na dose-dependent cell retraction and collapse. We show how engulfed\nZnO nanoparticles dissolve intracellularly, triggering actin filament bundling and structural changes in microtubules, transforming these highly dynamic\n25 nm diameter polymers into rigid\nmacrotubes of tubulin, severely affecting cell proliferation and survival. Our results\ndemonstrate that nano-ZnO causes acute cytoskeletal collapse that triggers necrosis, followed by a late reactive oxygen species (ROS)-dependent apoptotic process.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence study of LiNbO3<\/sub>:Cr3+<\/sup>; W4+<\/sup> at high pressure. Pressure dependence of spectroscopic parameters and local structure of Cr3+<\/sup>.<\/summary>
\n

Author<\/strong>(s): <\/strong>M.A.\nS\u00e1nchez-Alejo, F. Rodr\u00edguez, J.A. Barreda-Arg\u00fceso,\nI. Camarillo, C. Flores J., H. Murrieta S., J.M. Hern\u00e1ndez A, F. Jaque, E.\nCamarillo<\/p>\n\n\n\n

Source:<\/strong>  Optical Materials\nVolumen:<\/strong>  60  Pag<\/strong>.<\/strong>:<\/strong> 94<\/p>\n\n\n\n

DOI:<\/strong> http:\/\/dx.doi.org\/10.1016\/j.optmat.2016.07.013<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

In this study, the photoluminescence properties of congruent codoped LiNbO3<\/sub>:Cr3<\/sub>.; W4+<\/sup>, crystals have been\nsystematically investigated\nby performing photoluminescence studies at room temperature in the 0- 280 kbar pressure range. In particular, we focus on\nthe influence that hydrostatic pressure has on the 2<\/sup>E\/ 4<\/sup>A2 <\/sub>(R-lines) transitions of Cr3+<\/sup>.\nIt has been observed that the\npressure dependence of the spectral position of the R-lines associated\nwith both Cr3+<\/sup> centres\nand g shows a bilinear behaviour\nwith an abrupt\nslope change near 210 kbar. This change is\nrelated to the existence of a pressure-induced structural phase transition in the LiNbO3<\/sub> host. The analysis of experimental results provides the Racah\nparameters B and C and the crystal field parameter\n10Dq and their pressure and\nvolume, through the crystal field\ntheory and equation of state, dependences.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Role of high pressure for understanding luminescent phenomena<\/summary>
\n

Author<\/strong>(s): <\/strong>Rafael Valiente, Carlos Renero-Lecuna, Fernando Rodr\u00edguez, Jes\u00fas Gonz\u00e1lez<\/p>\n\n\n\n

Publication date: <\/strong>2016\/1\/31<\/p>\n\n\n\n

Source:<\/strong> Journal of Luminescence                    Volumen:<\/strong>  169        Pag<\/strong>.<\/strong>:<\/strong> 410<\/p>\n\n\n\n

DOI:<\/strong> http:\/\/dx.doi.org\/10.1016\/j.jlumin.2014.11.043<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

High-pressure techniques make possible to investigate\nthe changes in the electronic properties induced by modifications of the local or crystal\nstructure of the material without changing the chemical composition.\nThe different sensitivity of excited states to crystal-field\nstrength enables energy tuning of the states, which\nare eventually responsible for the optical\nproperties. It is possible to\ninduce resonance between levels producing exotic effects like upconversion as well as excited state crossover or high-spin to low-spin\ntransitions. Herein, we present selected\nexamples of high-pressure effect for understanding\nluminescent phenomena or even inducing\nnew ones.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Solarization-induced redox reactions in doubly Ce3+<\/sup>\/Mn2+<\/sup>-doped highly transmission glasses studied by optical absorption and photoluminescenc<\/summary>
\n

Author<\/strong>(s): <\/strong>Susana G\u00f3mez-Salces, Jos\u00e9 A Barreda-Arg\u00fceso, Rafael Valiente, Fernando Rodr\u00edguez<\/p>\n\n\n\n

Publication<\/strong>\ndate: <\/strong>2016\/12\/31<\/p>\n\n\n\n

Source:<\/strong>  Solar Energy Materials and Solar Cells      Volumen:<\/strong>  157   Pag<\/strong>.<\/strong>:<\/strong> 42<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.solmat.2016.05.010<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

This work investigates the photoluminescence properties of high transmission glass (HTG) doped with CeO2<\/sub> and MnO as well as their capability to transform the\nsolar spectrum by absorption\/emission via energy transfer from Ce3+<\/sup> to Mn2+<\/sup>\ninto a more efficient red- enhanced spectrum for traditional Si-based solar cells. We show that Mn3+<\/sup> and\nMn2+<\/sup> centers are formed in HTG, their relative concentration depending on the heat\ntreatment and the presence of other dopants like Ce3+<\/sup>.Co-doping with CeO2<\/sub> aims to stabilize\nMn2+<\/sup> …<\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Structural Metastability and Quantum Confinement in Zn1\u2013x<\/sub> Cox<\/sub>O Nanoparticles<\/summary>
\n

Author<\/strong>(s): <\/strong>Gloria Almonacid,\nRosa Mart\u00edn-Rodr\u00edguez, Carlos Renero-Lecuna, Julio\nPellicer-Porres, Sa\u00efd Agouram,\nRafael Valiente, Jesus Gonzalez,\nFernando Rodr\u00edguez, Lucie Nataf,\nDaniel R Gamelin, Alfredo Segura<\/p>\n\n\n\n

Publication date: <\/strong>2016\/7\/18<\/p>\n\n\n\n

Source:<\/strong> Nano letters         Volumen:<\/strong>  16   Issue<\/strong>:<\/strong> 8     Pag<\/strong>.<\/strong>:<\/strong> 5204<\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/acs.nanolett.6b02230<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

This paper investigates the electronic structure of wurtzite (W) and\nrock-salt (RS) Zn1\u2013x Cox O nanoparticles\n(NPs) by means of optical measurements under pressure (up to 25 GPa), X-ray absorption,\nand transmission electron microscopy. W-NPs were chemically synthesized at ambient conditions and RS-NPs were obtained by\npressure-induced transformation\nof W- NPs. In contrast to the abrupt\nphase transition in W\u2013Zn1\u2013xCoxO as thin film or single crystal, occurring sharply at about 9 GPa, spectroscopic\nsignatures of tetrahedral\nCo2+ …<\/p>\n<\/div><\/details><\/div>\n\n\n\n

The Significance of Bundling Effects on Carbon Nanotubes\u2019 Response to Hydrostatic Compression<\/summary>
\n

Author<\/strong>(s): <\/strong>Y. W. Sun,\u2028Ignacio\nHernandez, Jes\u00fas Gonz\u00e1lez, K. Scott, A. Sapelkin, F. Rodr\u00edguez, D. J. Dunstan<\/p>\n\n\n\n

Publication date: <\/strong>January 2016<\/p>\n\n\n\n

Source:<\/strong> The Journal of Physical\nChemistry C                        <\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

The study of the G-mode pressure coefficients\nof carbon nanotubes, reflecting the stiff sp2 bond pressure dependence, is essential to the\nunderstanding of their extraordinary mechanical properties as well as fundamental\nmechanics. However, it is hindered\nby the availability\nof carbon nanotubes samples only as bundles or isolated\nwith surfactants. Octadecylamine functionalized carbon nanotubes are mostly of a single diameter and\ncan be stably dispersed in\n1, 2-dichloroethane and chloroform without surfactants. Here we perform\nhigh pressure Raman spectroscopy on these tubes\nand obtain their\nexperimental G-mode pressure\ncoefficients for individual\ntubes and bundles. The + pressure coefficient for bundles is only\nabout half of that for individual tubes in 1, 2-dichloroethane and is\nabout two-thirds in chloroform. The G- pressure coefficient for bundles is\nabout one-third of G+ in 1,\n2-dichloroethane and about the\nsame in chloroform. These results for\nthe first time provide unambiguous experimental evidence of the significant effect of bundling on carbon\nnanotubes’ G-mode pressure coefficients, identifying it as one of the major\nreasons for the lack of consensus\non what the\nvalues should be in the literature.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Tris (bipyridine) Metal (II)-Templated Assemblies of 3D Alkali-Ruthenium Oxalate Coordination Frameworks: Crystal Structures, Characterization and Photocatalytic Activity in Water Reduction<\/summary>
\n

Author<\/strong>(s): <\/strong>Alla Dikhtiarenko, Pedro Villanueva-Delgado, Rafael Valiente,\nJos\u00e9 R Garc\u00eda, Jos\u00e9 Gimeno<\/p>\n\n\n\n

Publication date: <\/strong>2016\/2\/15<\/p>\n\n\n\n

Source:<\/strong> Polymers              Volumen:<\/strong>  8   Issue<\/strong>:<\/strong> 2       Pag<\/strong>.<\/strong>:<\/strong> 48<\/p>\n\n\n\n

DOI:<\/strong> http:\/\/dx.doi.org\/10.3390\/polym8020048<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong><\/p>\n\n\n\n

A series of 3D oxalate-bridged ruthenium-based coordination polymers with the\nformula of {[ZII(bpy)3<\/sub>][MIRu(C2<\/sub>O4<\/sub>)3<\/sub>]}n (ZII = Zn2+<\/sup>\n(1), Cu2+<\/sup> (3, 4), Ru2+<\/sup> (5, 6), Os2+<\/sup> (7, 8); MI\n= Li+<\/sup>, Na+<\/sup>; bpy\n= 2,2\u2019-bipyridine) and {[ZnII(bpy)3<\/sub>](H2<\/sub>O)[LiRu(C2<\/sub>O4<\/sub>)3<\/sub>]}n (2) has been synthesized at room temperature through a self-assembly reaction in aqueous media and characterized by single-crystal and powder X-ray diffraction, elemental analysis, infrared and diffuse reflectance UV\u2013Vis spectroscopy and thermogravimetric\nanalysis. The crystal structures of all compounds comprise\nchiral 3D honeycomb-like polymeric nets of the srs-type, which possess triangular anionic cages where [ZII(bpy)3<\/sub>]2+<\/sup> cationic\ntemplates are selectively embedded. Structural analysis reveals that the electronic\nconfiguration of the cationic guests is affected by\nelectrostatic interaction with the anionic\nframework. Moreover, the MLCT bands gaps values for 1\u20138 can be tuned in a rational way by judicious\nchoice of [ZII(bpy)3<\/sub>]2+<\/sup>\nguests. The 3D host-guest polymeric architectures can be used as self-supported heterogeneous photocatalysts for the reductive splitting\nof water, exhibiting photocatalytic activity for the evolution\nof H2<\/sub> under UV light irradiation.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2015<\/strong><\/p>\n\n\n\n

Anti-Cancer Cytotoxic Effects of Multiwalled Carbon Nanotubes<\/summary>
\n

Author<\/strong>(s):  <\/strong>Lorena Garcia-Hevia, Rafael\nValiente, Jesus Gonzalez, Jose Luis Fernandez-Luna, Juan C.\nVillegas and Monica L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> Current Pharmaceutical\nDesign.                   <\/em>Volumen: <\/strong>21                       Pag<\/strong>.<\/strong><\/em> 1920 – 1929<\/p>\n\n\n\n

Abstract<\/strong>: Recent research\nhas opened new alternatives\nto traditional chemotherapy treatments using nanomaterials as cytotoxic agents. Anti-cancer nanomedicines do not require specific\ntarget sites on key proteins or\ngenes to kill cancer cells and have radically different mechanisms to interact with\nthe living matter. Among 1D nanomaterials, multiwalled carbon nanotubes (MWCNTs) have the intrinsic\nability to bind tubulin and interfere with microtubule dynamics, mimicking the effect\nof traditional cytotoxic microtubule-binding agents such as paclitaxel (taxol\u00ae). Here, we review the\ncytotoxic properties of MWCNTs and show a direct pro-apoptotic effect of these nanomaterials in vitro in different cancer cell lines and tumor cells obtained from surgical specimens.\nUnderstanding the bio-synthetic relationship between MWCNTs and microtubules could serve to improve\nthese nanomaterials to be used as broad\nspectrum antineoplastic agents in combination to traditional microtubule-binding treatments, thus avoiding drug\nresistance mechanisms in cancer cells.<\/p>\n\n\n\n

DOI: <\/strong>10.2174\/1381612821666150302144101<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spin state, Jahn-Teller effect and metallization processes in CoCl2<\/sub> and CoF3<\/sub><\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>F.\nRodr\u00edguez \u2028<\/p>\n\n\n\n

Source:<\/strong> International\nConference: Study of Matter at Extreme Conditions\n(SMEC2015)                     Florida International University,\nFort Lauderdale (FL, EEUU)         Fecha:\n8-15 marzo 2015<\/p>\n\n\n\n

Abstract<\/strong>: The optical, electrical and magnetic properties\n(electronic properties) of transition-metal-ion (TM<\/em>) compounds strongly depend on the TM<\/em> ground-state spin. In oxides and halides of Mn3+<\/sup>(3d4<\/sup>); Co2+<\/sup> (3d7<\/sup>), or Fe2+<\/sup> and Co3+<\/sup>(3d6<\/sup>),\nthe electronic ground state can be relatively close to the spin crossover\ntransition. Hence, subtle structural distortions around the TM<\/em> due to the Jahn-Teller\neffect affecting either the low-spin (LS), intermediate-spin (IS) or high-spin\n(HS) state may favour stabilization of either spin ground state upon\ncompression, eventually yielding metallization. The prediction of which spin\nstate will be stable at given conditions of pressure and temperature is not\neasy, particularly, in sixfold coordinated TM<\/em> compounds where the Jahn-Teller effect can play a crucial role. In many cases\ntheir structural characterization is hard to accomplish through diffraction\ntechniques due to topological disorder induced by dynamics or spin state mixing\nand thus adequate structural\ncharacterization<\/em> often deserves using complementary techniques. <\/em>Here we present a high-pressure\nspectroscopy study to explore the spin state and associated structural distortions, and the insulating to metal transition in TM<\/em> halides undergoing spin crossover transitions\nupon compression. The combination of optical spectroscopy and x-ray diffraction experiments, and ab\ninitio<\/em> DFT calculations allows\nus to describe both the structural\nphase transition sequence, spin crossover phenomena\nand metallization process\nin the charge-transfer compound CoCl2<\/sub>. Besides,\nwe also investigate\non the different\nspin crossover phenomena exhibited\nby Jahn-Teller systems involving Mn3+<\/sup>\nand Co3+<\/sup> fluorides. The\npossible involvement of the strong Jahn-Teller\nIS state in the spin\ncrossover in CoF3<\/sub> will be discussed in connection with high-pressure experiments carried out in the isoelectronic\nFe2+<\/sup> in (Mg,Fe)O and its\ngeophysical implications. The reliability of DFT methods to predict\nspin crossover phenomena will\nbe also discussed.<\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Influence of chirality and bundling on G-mode pressure dependence in SWCNT<\/summary>
\n

Author<\/strong>(s): <\/strong>Y.W.Sun, I.\nHern\u00e1ndez, J. Gonz\u00e1lez, I.F. Crowe, M.P. Halsall, K.\nScott, K.J. Donovan, A. Sapelkin, D.J. Dunstan, F. Rodr\u00edguez<\/strong><\/p>\n\n\n\n

Source:<\/strong> International\nConference: Study of Matter at Extreme Conditions\n(SMEC2015)   Lugar\nde celebraci\u00f3n: Florida International University,\nFort Lauderdale (FL, EEUU)       Fecha:\n8-15 marzo 2015-<\/p>\n\n\n\n

Abstract<\/strong>: Here we\npresent investigations on G-mode pressure\ndependence of single-wall carbon nanotubes(SWCNT). The aim\nis to clarify\nthe data dispersion of G-mode pressure shifts\nreported in theliterature\nand attributed to distinct factors. Trying to identify\nthe main factors affecting theirpressure dependence, we show that, not\nonly solvents employed as pressure transmitting media, butalso bundling and chirality can significantly influence G-mode pressure coefficients.\nThe study ofG-Mode pressure coefficients, reflecting the stiff sp2 bond pressure dependence, is important tounderstand\ntheir extraordinary mechanical properties. However, this information\nis often hinderedby the availability of CNTs samples as bundles or isolated with\nsurfactants. Here we perform aseries of high pressure Raman\nspectroscopy experiments on selected SWCNT samples. We obtainexperimental\nG-Mode pressure coefficients, which are unaffected by surfactants,\nfor individualtubes and bundles, by means\nof octadecylamine functionalized\nSWCNTs. The G+ pressurecoefficient for bundles is only\nabout half of that for individual tubes in 1,2-dichloroethane and isabout\ntwo-thirds in chloroform. For bundles, the\nG pressure coefficient is about one-third\nof G+ in1, 2-dichloroethane and about the same in chloroform.\nSimilarly we find that bundled\npristineSWCNTs of (6,5) and (9,11) chiralities having the same diameter\nshow significantly differentpressure\ncoefficients.These results provide experimental evidences of\nbundling and chirality effects on SWCNT G-modepressure coefficients, claiming them as probable reasons for the\ndispersion of data found in\ntheliterature<\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

Control of infrared cross-relaxation in LiNbO3:Tm3+<\/sup> through high-pressur<\/summary>
\n

Author<\/strong>(s): <\/strong>M Quintanilla, E Cantelar, F\nCuss\u00f3, J A Barreda-Arg\u00fceso,\nJ Gonz\u00e1lez, R. Valiente and F Rodr\u00edguez\n<\/p>\n\n\n\n

Source:<\/strong>  Optical Materials\nExpress      Volumen<\/strong>:<\/strong>  5\n\n\t Pag<\/strong>:<\/strong> 1168<\/p>\n\n\n\n

DOI<\/strong>:<\/strong>  10.1364\/OME.5.001168\n \n\n \n<\/p>\n\n\n\n

Abstract<\/strong>: <\/strong>The cross-relaxation process between the lower excited\nstates of thulium ions has a strong influence on its\nmain infrared emissions, but also in the population\nof higher excited states that lead to characteristic blue upconversion. This work investigates\nthis process in LiNbO3:Tm3+<\/sup>\nby means of time-resolved spectroscopy at high pressure. It is\ndemonstrated that through the application\nof high-pressure it is possible to\nenhance its probability and to investigate its influence on the\nphotoluminescence spectra\nand corresponding lifetimes\nof Tm3+.<\/sup> The results\nare analyzed in terms of the effect of high\npressure on parameters such as Tm3+<\/sup>-Tm3+<\/sup>\ndistance through the Eq. (-)of-state\nof LiNbO3, refractive index\nor Tm3+<\/sup>– Tm3+<\/sup> energy transfer characteristics (absorption\/emission overlap integral), to conclude that the\nmajor multipole interaction responsible for crossrelaxation is the quadrupole-quadrupole\ninteraction. This conclusi\u00f3n\nsupports and clarifies previous dynamical models for energy\ntransfer on the basis of spectroscopic studies carried out in LiNbO3:Tm3+<\/sup> as a function\nof Tm3+<\/sup> concentration.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2014<\/strong><\/p>\n\n\n\n

POSTER:\u00a0\u00a0\u00a0\u00a0 Long-lived, visible-range sensitized IR emission in Yb(III) perchlorotropolonate complexes<\/em><\/summary>
\n

Author<\/strong>(s):  <\/strong>I Hern\u00e1ndez; Y-X. Zheng, M. Motevalli, R.H.C. Tan,\nW.P. Gillin, P.B. Wyatt <\/strong><\/p>\n\n\n\n

Source:<\/strong> Congreso: 5th<\/sup> International Workshop on Photoluminescence in Rare Earths (PRE\u201914). San Sebastian, 13-16 Mayo 2014<\/p>\n\n\n\n

Abstract<\/strong>: Some of our newly produced Yb(III) compounds based on pentachlorotropolonate\nshow the longest emission lifetime and efficiency (\uf074\uf020\uf03d\uf020180\n\uf06ds, \uf068\uf020\uf07e\uf02015%) for non-fluorinated IR-emitting\norganolanthanides complexes. Interestingly, they are\nsensitized via low energy lying states in the orange-red region of the spectrum.\nIn this contribution we report the chemical and photophysical\ncharacterization and discuss the rules governing the excitation and emission\nproperties. Our work shows that the use of chlorinated ligands allows for an\nefficient emission by reducing non-radiative\nquenching and the sensitization via states with a triplet character, which are\npopulated thanks to the enhanced inter-system crossing. These materials may be\nof interest for devices and applications in telecommunication technologies and\nbiology.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Efficient Cooperative Energy Transfer Upconversion in Organolanthanides<\/em><\/summary>
\n

uthor<\/strong>(s):  <\/strong>H. Ye, N. Pathumakanthar, Y.X. Zheng, P.B. Wyatt, W.P. Gillin, I. Hern\u00e1ndez<\/strong><\/p>\n\n\n\n

Source:<\/strong> 5th<\/sup>\nInternational Workshop on Photoluminescence in Rare Earths (PRE\u201914). San Sebastian,\n13-16 Mayo 2014<\/p>\n\n\n\n

Abstract<\/strong>: Following understanding of the excited state\ndynamics in long-lived infra-red emitting organolanthanides [1], we have produced relatively\nefficient infra-red (IR) to\nvisible upconverting polymers\nbased on lanthanide organic complexes [2]. The idea is to exploit\nthe long-lived states of Yb3+ perfluorinated complexes and the cooperative energy transfer to efficient emitters\nwith a wide gap, such as Eu3+ or Tb3+ (which is resonant\nwith the excited Yb pairs\u2019 states). In this paper we report\nvarious families of compounds (with different ligands and emitters) showing IR to visible upconversion. We describe some basic design rules derived from the\nobserved behavior and chemical nature, and discuss the advantages,\nlimitations and possibilities\nof this new kind of compounds<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Organic erbium-doped optical gain materials<\/summary>
\n

Author<\/strong>(s):  <\/strong>H.O. Ye, Y. Peng, Z. Li, P.B. Wyatt, I.\nHern\u00e1ndez, W.P. Gillin<\/strong><\/p>\n\n\n\n

Source:<\/strong> 5th<\/sup>\nInternational Workshop on Photoluminescence in Rare Earths (PRE\u201914). San Sebastian,\n13-16 Mayo 2014<\/p>\n\n\n\n

Abstract<\/strong>: Organic erbium-doped materials for application\nof optic amplifier at telecommunication wavelength have been studied\nfor decades. Here we show a potential organic optical gain system\nwhich could be operated under low pump power\ndensity. The fully-fluorinated organic erbium complex [Er(f-tpip)3<\/sub>] was mixed with a fully-fluorinated\norganic zinc complex\n[Zn(F-BTZ)2<\/sub>] by using\nthe technique of vacuum-film-deposition. The fabulous sensitization\nfrom Zn(F-BTZ)2<\/sub> to\nEr(f-tpip)3<\/sub> in a broad\nvisible band (UV ~ 450 nm) has been\nobserved as well as the emission lifetime\nat 1.54 \u00b5m is kept as long as ~ 0.8 ms (the quantum yield is ~ 7%). The sensitization is ~ 104<\/sup> bigger than intrinsic excitation of erbium. The emission of this co-doped system\nwas going to be saturated when a co-doped film was excited by\nthe low power\nof a dye laser (~200 mW\/cm2<\/sup>).\nMoreover, this system has been integrated into an organic light emitting diodes (OLED) demonstrating that the energy transfer of sensitization is dominated by triplet\nstates of excited Zn(F-BTZ)2<\/sub>.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced Pr3+<\/sup> 3<\/sup>P0<\/sub> luminescence in cubic Y2<\/sub>O3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>Alok\nM. Srivastava , Carlos Renero-Lecuna\n, David Santamar\u00eda-P\u00e9rez , Fernando Rodr\u00edguez , Rafael Valiente <\/strong><\/p>\n\n\n\n

Source:<\/strong> Journal of Luminescence        <\/em>            Vol.:   \n146                Pag.: 27-32<\/p>\n\n\n\n

Abstract<\/strong>: An explanation\nfor the puzzling\nabsence of luminescence from the Pr3+<\/sup> 3<\/sup>PJ[1\/40,1,2]<\/sub>\nstates in C-Ln2<\/sub>O3<\/sub> (cubic; Ln3+<\/sup> =Lu3+<\/sup>, Y3+<\/sup>, Gd3+<\/sup>)\nfamily of materials is provided by\nconducting a study of the emission properties\nof C-Y2<\/sub>O3<\/sub>:Pr3<\/sup>+<\/sup>\nunder applied hydrostatic pressure. Above 7 GPa, electronic\ntransitions from the Pr3+ 3<\/sup>PJ[=0,1,2]<\/sub> states are observed in the emission spectrum\nof C-Y2<\/sub>O3<\/sub>:Pr3+ at room temperature and below. The experimental data reveal that the crystal-field\nsplit Pr3+<\/sup> 4<\/sup>f15<\/sup>d1 configuration is located entirely within the host lattice conduction band and that the promotion\nof the electron to the Pr3+<\/sup> 4<\/sup>f1<\/sub>5<\/sup>d1<\/sub>\nstate produces a self-trapped\nexciton-like state with the configuration,\n[Pr4+<\/sup> eCB], where\neCB indicates an electron in the host lattice conduction band. Upon excitation, the exciton-like state bypasses the upper\nemitting 3<\/sup>PJ[=0,1,2]<\/sub> states and directly feeds the lower\nemitting 1<\/sup>D2<\/sub> state. This explains\nthe absence of optical transitions from the Pr3+ 3<\/sup>PJ[=0,1,2]<\/sub>\nstates in the emission spectrum of C-Y2<\/sub>O3<\/sub>:Pr3+<\/sup>\nAt ambient pressure. At high pressures, emission transitions from the Pr3+ 3<\/sup>PJ[=0,1,2]<\/sub>\nstates are observed because of the localization of the Pr3+<\/sup>\n4<\/sup>f1<\/sub>5<\/sup>d1<\/sub> state\nto below the host lattice conduction band edge.<\/p>\n\n\n\n

DOI:<\/strong> dx.doi.org\/10.1016\/j.jlumin.2013.09.028<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure crystallographic and spectroscopic studies on two molecular dithienylethene switche<\/summary>
\n

Author(s): <\/strong>Christopher H. Woodall, Simon\nK. Brayshaw, Stefanie Schiffers, David R. Allan, Simon Parsons, Rafael Valiente\nand Paul R. Raithby<\/p>\n\n\n\n

Source:<\/strong> CrystEngComm     Vol.:    16                   Pag.:\n2087<\/p>\n\n\n\n

Abstract<\/strong>: Single crystals of the dithienylethene\ncompounds, 1,2-bis(2-methylbenzothiophen-3-yl)perfluorocyclopentene\n1 and 1,2-bis(2,5-dimethylthiophen-3-yl)perfluorocyclopentene 2 undergo\npressure-induced single-crystal to single-crystal phase transitions between\n4.45\u20135.35 GPa and 4.15\u20135.70 GPa, respectively. For 1, there is a\nsmooth reduction in unit-cell volume of ~20% from ambient pressure to 4.45 GPa,\nfollowed by a dramatic reduction in volume that coincides with a 7.7% increase\nin the b axis length. Above the pressure of 5.38 GPa a smooth volume reduction\ncontinues. In contrast, for 2, there is a continuous change in unit-cell volume\nwith an observed space group change from C2\/c to P21\/c, between the pressures\nof 4.15 and 5.70 GPa. In the crystals of 1 between 4.45 and 5.38 GPa adjacent\nmolecules slide over each other and the dominant stacking interaction changes\nfrom a thiophene\u22efthiophene interaction at 4.45 GPa to a benzothiophene\u22efbenzothiophene interaction at 5.38 GPa\nand, within each molecule, the benzothiophene groups show a significant\nreorientation at the phase transition. In 2 there is a loss of molecular\nsymmetry, concomitant with the change in space group, at the phase transition\nwith the asymmetric unit changing from containing half a unique molecule to two\nindependent molecules. The molecules show significant reorientations of their\nring systems. The nature of the observed transition in 1 was investigated using\nsolid-state computational methods to prove the superior thermodynamic stability\nof the high-pressure phase to the lower pressure phase at pressures above 5.38\nGPa. Solid state UV-Vis spectroscopy of 1, over the pressure range from ambient\nto 15.4 GPa showed that the compound displayed piezochromism with a significant\nred shift in the \u03c0\u2013\u03c0* absorption band and a colour change in\nthe crystal from colourless to red with increasing pressure.<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/c3ce41933a<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Effects of Cu2+<\/sup> doping and pressure on the exchange-mediated exciton dynamics in one-dimensional N(CH3<\/sub>)4<\/sub>MnCl3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>Lucie Nataf,\nJos\u00e9 Antonio Barreda-Arg\u00fceso, Rafael Valiente, Jes\u00fas\nGonz\u00e1lez, y Fernando Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B               Vol.:    89                   Pag.: 115120<\/p>\n\n\n\n

Abstract<\/strong>: This work\ninvestigates the Mn2+<\/sup>\nelectronic structure and exciton dynamics in one-dimensional (1D) N(CH3<\/sub>)4<\/sub>MnCl3<\/sub>\n(TMMC) through time-resolved excitation\/emission spectroscopy and absorption measurements in the 0\u201310 GPa pressure range for different Cu2+<\/sup>\ndoping concentrations. The\nlocal and crystal structures\nhave been analyzed by Raman\nspectroscopy and x-ray absorptionmeasurements at theMnK<\/em>edge showing that the 1D chain\nstructure is maintained in the whole explored pressure range. We show that both\nthe first Mn2+<\/sup> absorption band, 4<\/sup>T<\/em>1<\/sub>(G<\/em>),\nand its associated emission band experience very large pressure\nredshifts, which are associated with the crystal anisotropy\nproviding large axial ligand fields at the Mn2+<\/sup> site that increase with\npressure. The red emission at 633 nm shows a large pressure variation of 22 nm\/GPa (50 meV\/GPa)\nmaking TMMC a suitable probe for using\nas a photoluminescence (PL) pressure\ngauge in the low-pressure regime. The energy-transfer\nexciton dynamics and trapping at non-PL centers have been explained through changes of the intrachain Mn-Mn exchange interaction and Cu2+<\/sup>-trap concentration carried out by\napplying pressure and\ndoping, respectively. The model demonstrates that an increase\nof exchange interaction favors both the\npumping capability and energy transfer yielding exciton migration. Under these conditions,\nwe show that pressure enhances the PL efficiency of TMMC provided that the\nCu2+<\/sup> concentration responsible\nfor the PL quenching is below\n0.001 mol %. However, between\n0.001% and 0.1%, the PL intensity\nreduces with pressure, and above 0.1%, the PL is practically quenched even at ambient conditions.<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.89.115120<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Visible-Range Sensitization of Er3+-Based Infrared Emission from Perfluorinated 2-Acylphenoxide Complexes<\/summary>
\n

Author<\/strong>(s):  <\/strong>Y. Peng;\nH. Ye; Z. Li, M. Montevalli, I. Hern\u00e1ndez,\nW.P. Gillin, P.B. Wyatt<\/strong><\/p>\n\n\n\n

Source:<\/strong> Journal<\/em> of Physical\nChemistry Letters                      <\/em>Volumen:<\/strong> 5              Pag<\/strong>.:<\/strong> 1560<\/em><\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

Abstract<\/strong>: Five new fully\nfluorinated acylphenoxide ligands, which are aromatic analogues of \u03b2-diketonates, provide visible photosensitization of the Er3+  4I13<\/sub><\/sup>\/2<\/sub> \u2192 4<\/sup>I15\/2<\/sub>\nemission at 1540\nnm (of interest for telecommunications) via the \u201cantenna\neffect\u201d, as observed in\nCs[ErL4<\/sub>] compounds. Depending\non the chemical\nfunctionalization, the excitation wavelength can be tuned in the 400\u2013650 nm range. Decay\ntimes for the solids are in the range of 7\u201316 \u03bcs, proving that the\ncomplexes can be of interest\nfor a number of optoelectronic and photonic applications.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence in ZnO:Co2+ (0.01%\u22125%) Nanoparticles, Nanowires, Thin Films, and Single Crystals as a Function of Pressure and Temperature: Exploring Electron\u2212Phonon Interactions<\/summary>
\n

Author<\/strong>(s): <\/strong>Carlos Renero-Lecuna, Rosa Mart\u00edn-Rodr\u00edguez, Jesus\nA. Gonz\u00e1lez, Fernando Rodr\u00edguez, Gloria Almonacid, Alfredo Segura, Vicente Mu\u00f1oz-Sanjose\u0301,\nDaniel R. Gamelin, y Rafael Valiente<\/p>\n\n\n\n

Source:<\/strong> Chem. Mater.       <\/em>            Vol.:    26                   Pag.: 1100\u22121107<\/p>\n\n\n\n

Abstract<\/strong>: This work\ninvestigates the electronic structure and photoluminescence properties of\nCo2+<\/sup>-doped ZnO\nand their pressure and temperature dependences through high-resolution absorption and emission spectroscopy as a function of Co2+<\/sup>\nconcentration and their structural conformations as a\nsingle crystal, thin film, nanowire, and nanoparticle. Absorption and emission spectra of diluted ZnO:Co2+<\/sup>\n(0.01 mol %) can be related to\nthe 4<\/sup>T1<\/sub>(P) \u2192 4<\/sup>A2<\/sub>(F)\ntransition of CoO4<\/sub> (Td),\ncontrary to MgAl2<\/sub>O4<\/sub>:Co2+<\/sup>\nand ZnAl2<\/sub>O4<\/sub>:Co2+<\/sup> spinels\nin which the red emission is ascribed\nto the 2<\/sup>E(G)\n\u2192 4<\/sup>A2<\/sub>(F) transition. We show that the\nlow-temperature emission\nband consists of a 4<\/sup>T1<\/sub>(P) zero-phonon line and a phonon-sideband,\nwhich is described in terms of the phonon density\nof states within an intermediate coupling scheme (S = 1.35) involving all ZnO\nlattice phonons. Increasing pressure to the sample\nshifts the zerophonon line to higher energy as expected for the\n4<\/sup>T1<\/sub>(P) state upon compression. The low-temperature emission quenches above 5 GPa as a consequence of the pressure-induced wurtzite to rocksalt structural\nphase transition, yielding a change of Co2+<\/sup>\ncoordination from 4-fold Td to 6-fold Oh . We also show that\nthe optical properties of ZnO:Co2+<\/sup> (Td)\nare similar, independent of the\nstructural conformation of the host and the cobalt concentration. The Co2+ <\/sup>enters into regular Zn2+<\/sup> sites\nin low concentration systems (less than\n5% of Co2+<\/sup>), although some\nslight shifts and peak broadening appear as the dimensionality\nof the sample decreases. These structural effects on the optical\nspectra are also supported by Raman\nspectroscopy<\/p>\n\n\n\n

DOI:<\/strong> dx.doi.org\/10.1021\/cm403371n\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Resonance Raman spectroscopy of carbon nanotubes: pressure effects on G-mode<\/summary>
\n

Author<\/strong>(s):  <\/strong>Y.W. Sun,\nI. Hern\u00e1ndez, A.J. Ghandour, C. Rice, I.F. Crowe, M.P. Halsall, A. Sapelkin, J. Gonzalez, F. Rodriguez and D.J. Dunstan<\/p>\n\n\n\n

Source:<\/strong> High Pressure Research.                    <\/em>Volumen:\n<\/strong>4              Pag.191-197<\/strong><\/em><\/p>\n\n\n\n

Abstract<\/strong>: We use 488 and 568 nm laser Raman spectroscopy under high pressure\nto selectively follow evolution of Raman G-mode signals\nof single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The\nG-mode pressure coefficients of tubes from our previous\nwork are consistent with the thick-wall\ntube model. Here we report\nthe observation of well-resolved G-minus peaks in the Raman\nspectrum of SWCNTs in a diamond-anvil cell. The pressure coefficients\nof these identified tubes in water, however, are unexpected, having the high\nvalue of over 9 cm\u22121<\/sup> GPa\u22121<\/sup>\nfor the G-plus and the G-minus, and surprisingly the shift rates of the same tubes\nin hexane have clearly lower values.\nWe also report\nan abrupt increase of G-minus peak width at about\n4 GPa superposed on a continuous peak broadening with pressure.<\/p>\n\n\n\n

DOI: <\/strong>10.1080\/08957959.2013.878714<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Concentration dependence of the up- and down-conversion emission colours of Er3+<\/sup>-doped Y2<\/sub>O3<\/sub>: a time-resolved spectroscopy analysis<\/summary>
\n

Author<\/strong>(s):  <\/strong>H. Ye, Z. Li, Y. Peng,\nC.-C. Wang, T-Y Li, Y.-X. Zheng, A. Sapelkin, G, Amadopoulos,I.\nHern\u00e1ndez, P.B. Wyatt, W.P. Gillin<\/p>\n\n\n\n

Source:<\/strong> Nature<\/em> Materials             <\/em>Volumen:<\/strong> 13                       Pag<\/strong>.:<\/strong> 382<\/em><\/p>\n\n\n\n

Abstract<\/strong>: Modern telecommunications rely on the transmission\nand manipulation of optical\nsignals. Optical amplification plays a vital part in this technology,\nas all components in a real\ntelecommunications system\nproduce some loss. The two main\nissues with present amplifiers, which rely on\nerbium ions in a glass matrix, are the difficulty in integration onto a single substrate and the need of high pump\npower densities to produce gain. Here we show a potential organic optical amplifier material that demonstrates population inversion when pumped from\nabove using low-power visible light. This system is integrated\ninto an organic\nlight-emitting diode demonstrating that electrical pumping can be achieved. This opens the possibility of direct electrically driven optical amplifiers and optical circuits. Our results\nprovide an alternative approach to producing low-cost\nintegrated optics that is compatible with existing silicon\nphotonics and a different route to an\neffective integrated optics technology.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Concentration dependence of the up- and down-conversion emission colours of Er3+<\/sup>-doped Y2<\/sub>O3<\/sub>: a time-resolved spectroscopy analysis <\/summary>
\n

Haizhou Lu<\/a>,   William P. Gillin<\/a> and   Ignacio Hern\u00e1ndez<\/a> <\/p>\n\n\n\n

Phys<\/em><\/strong>. Chem. Chem. Phys.<\/em><\/strong>, 2014, Advance Article<\/p>\n\n\n\n

DOI: <\/strong>10.1039\/C4CP02028F<\/p>\n\n\n\n

In this paper, a series\nof Er3+<\/sup>-doped Y2<\/sub>O3<\/sub> samples\nare systematically investigated,\nfocusing on the effect of the\ndoping concentration on the emission lifetime\nand spectrum under both 488 nm and 980 nm excitations. Decay times of the 4<\/sup>S3\/2<\/sub> and 4<\/sup>F9\/2<\/sub> emitting\nstates under 488 nm and 980 nm excitations\nare found to be different and concentration dependent. We explain\nthese variations in terms of the changes\nin the up-conversion routes caused by\nthe predominance of energy exchanges that involve the\nlowest lying excited states.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Bulk and Molecular Compressibilities of Organic\u2212Inorganic Hybrids [(CH3)4N]2MnX4 (X = Cl, Br); Role of ntermolecular Interactions<\/summary>
\n

Author<\/strong>(s): <\/strong>Jose Antonio Barreda-Arg\u00fceso,\nLucie Nataf, Yamilet Rodr\u00edguez-Lazcano, Fernando Aguado, Jes\u00fas Gonz\u00e1lez, Rafael\nValiente, Fernando Rodr\u00edguez, Heribert Wilhelm and\nAndrew P. Jephcoat<\/p>\n\n\n\n

Source:<\/strong> Inorg. Chem.                   Vol.:<\/strong>   \n53                  Pag<\/strong>.:<\/strong> 10708\u221210715<\/p>\n\n\n\n

Abstract<\/strong>: This work reports an X-ray\ndiffraction, X-ray absorption, and Raman spectroscopy study of [(CH3<\/sub>)4N]2<\/sub>MnX4<\/sub> (X = Cl, Br) under pressure. We show that both\ncompounds share a similar phase\ndiagram with pressure. A P21<\/sub>\/c monoclinic\nstructure describes precisely\nthe [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnCl4<\/sub>\ncrystal in the 0.1\u22126 GPa range, prior to cristal decomposition and amorphization, while [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnBr4<\/sub>\ncan be described by a Pmcn orthorhombic structure in its stability pressure range of 0\u22123 GPa. These materials are attractive systems for pressure studies\nsince they are readily compressible through the weak\ninteraction between organic\/inorganic [(CH3<\/sub>)4<\/sub>N+<\/sup>\/MnX4<\/sub>2\u2212<\/sup>]\ntetrahedra through hydrogen bonds and contrast with the\nsmall compressibility of both tetrahedra. Here we determine the equation-of-state (EOS) of each crystal and compare it with the corresponding\nlocal EOS of the MnX4<\/sub>2\u2212<\/sup> and\n(CH3<\/sub>)4<\/sub>N+ <\/sup>tetrahedra,\nthe compressibility of which is an\norder and 2 orders of magnitude smaller than the crystal\ncompressibility, respectively,\nin both chloride and bromide. The variations\nof the Mn\u2212Cl bond distance\nobtained by extended X-ray absorption fine structure and the frequency of the totally symmetric \u03bd1(A1) Raman mode of MnCl4<\/sub>2\u2212\n<\/sup>with pressure in [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnCl4<\/sub>\nallowed us to determine the associated Gr\u00fcneisen parameter (\u03b3loc = 1.15) and hence an accurate\nlocal EOS. On the basis of a local compressibility model, we obtained\nthe Gr\u00fcneisen parameters and corresponding variations of the intramolecular Mn\u2212Br and C\u2212N bond distances of MnBr42\u2212 (\u03b3loc\n= 1.45) and (CH3<\/sub>)4<\/sub>N+<\/sup> (\u03b3loc\n= 3.0) in [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnBr4<\/sub>.<\/p>\n\n\n\n

DOI:<\/strong> dx.doi.org\/10.1021\/ic501854g<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Multiwalled Carbon Nanotubes Hinder Microglia Function Interfering with Cell Migration and Phagocytosis<\/summary>
\n

Author(s): <\/strong>Juan\nC. Villegas , Laura \u00c1lvarez-Montes , Lidia Rodr\u00edguez-Fern\u00e1ndez , Jes\u00fas Gonz\u00e1lez\n, Rafael Valiente, and M\u00f3nica L. Fanarraga <\/p>\n\n\n\n

Source:<\/strong> Advance Healthcare\nMaterials            <\/em>            Vol.:    3                     Pag.:\n424-432<\/p>\n\n\n\n

Abstract<\/strong>: The intranasal drug delivery route provides exciting expectations\nregarding the application of engineered nanomaterials as nano-medicines or\ndrugdelivery vectors into the brain. Among nanomaterials, multiwalled CNTs (MWCNTs)\nare some of the best candidates for brain cancer therapy since they are well\nknown to go across cellular barriers and display an intrinsic ability to block\ncancer cell proliferation triggering apoptosis. This study reveals that\nmicroglial cells, the brain macrophages and putative vehicles for MWCNTs into\nthe brain, undergo a dose-dependent cell division arrest and apoptosis when\ntreated with MWCNTs. Moreover, it is shown that MWCNTs severely interfere with\nboth cell migration and phagocytosis in live microglia. These results lead to a\nre-evaluation of the safety of inhaled airborne CNTs and provide strategic\nclues of how to biocompatibilize MWCNTs to reduce brain macrophage damage and\nto develop new nanodrugs.<\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/adhm.201300178<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Exchange Interactions at the Origin of Slow Relaxation of the Magnetization in {TbCu3} and {DyCu3} Single-Molecule Magnets \u00a0<\/summary>
\n

Author<\/strong>(s):  <\/strong>Fraser J. Kettles,\nVictoria A. Milway, Floriana\nTuna, Rafael Valiente, Lynne H. Thomas, Wolfgang Wernsdorfer, Stefan T. Ochsenbein\nand Mark Murrie<\/p>\n\n\n\n

Source:<\/strong> Inorg. Chem        <\/em>Volumen: <\/strong>53                       Pag<\/strong>.:<\/strong> <\/em>8970\u22128978<\/p>\n\n\n\n

Abstract<\/strong>: New {TbCu3} and {DyCu3}\nsingle-molecule magnets (SMMs) containing a low-symmetry LnIII center (shape measurements relative to a trigonal dodecahedron and biaugmented\ntrigonal prism are 2.2\u22122.3) surrounded\nby three CuII metalloligands are reported. SMM behavior is confirmed by\nfrequency-dependent out-of-phase ac susceptibility\nsignals and single-crystal temperature and sweep rate dependent hysteresis loops. The ferromagnetic exchange interactions between the central LnIII ion and the three CuII ions\ncould be accurately measured by inelastic\nneutron scattering (INS) spectroscopy and modeled effectively. The excitations observed by INS correspond to flipping of CuII spins and appear at energies similar to the thermodynamic\nbarrier for relaxation of the magnetization, \u223c15\u221220 K, and are thus at the origin of the\nSMM behavior. The magnetic quantum number Mtot of the cluster\nground state of {DyCu3} is an integer,\nwhereas it is a half-integer for {TbCu3}, which explains their vastly different quantum tunneling of the magnetization behavior despite similar energy barriers<\/p>\n\n\n\n

DOI: <\/strong>dx.doi.org\/10.1021\/ic500885<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical nanothermometer based on the calibration of the Stokes and upconverted green emissions of Er3+ ions in Y3Ga5O12 nano-garnets<\/summary>
\n

Author<\/strong>(s):  <\/strong>S. F. Le\u00f3n-Luis, V. Monteseguro, U. R. Rodr\u00edguez-Mendoza, M. Rathaiah, V. Venkatramu, A. D.\nLozano-Gorr\u00edn,a R. Valiente, A. Mu\u00f1oz and V. Lav\u00edn<\/p>\n\n\n\n

Source:<\/strong> RSC Adv.              <\/em>Volumen:\n<\/strong>4              Pag.:<\/strong><\/em>57691<\/p>\n\n\n\n

Abstract<\/strong>: The temperature-dependent\ngreen luminescence of Y3Ga5O12\nnano-garnets doped with different concentrations of Er3+ ions has been measured from\n300 to 850 K and, in more detail,\nin the biological range from 292 to 335 K. The green\nemissions were obtained by excitation\nunder 488 nm blue or 800 nm\nnear-infrared laser radiations.\nBoth excitations give rise to\nbright green luminescence that can be seen by the\nnaked eye, and which can be associated either with Stokes processes, i.e. multiphonon relaxations followed by green spontaneous\nemission, in the former case or with infrared-to-visible\nupconversion processes in the latter. The\ntemperature-induced changes\nin the Er3+ green emissions have been calibrated for both excitations\nand results point to a strong dependence\non the concentration\nof optically active Er3+ ions.\nThe maximum value of the thermal\nsensitivity, 64 ! 10″4 K\u00bb1 at 547 K, has been obtained for\nthe nano-garnets doped with the\nlowest concentration of Er3+\nions, which is one of the\nhighest values found in the literature.\nThese results allow to conclude\nthat a relatively low concentration of optically active ions is advisable and the changes induced\nby temperature on the Green emissions\nare independent of the\nlaser excitation radiation used, which is\nnecessary to calibrate the temperature\nof the immediate environment of the Er3+-doped Y3Ga5O12 nano-garnets.<\/p>\n\n\n\n

DOI: <\/strong>10.1039\/c4ra11565a<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Organo-erbium systems for optical amplification at telecommunications wavelength<\/summary>
\n

Author(s):\n <\/strong>H. Ye, Z. Li, Y. Peng, C.-C.\nWang, T-Y Li, Y.-X. Zheng, A. Sapelkin, G, Amadopoulos,I. Hern\u00e1ndez,\nP.B. Wyatt, W.P. Gillin<\/p>\n\n\n\n

Source:<\/strong> Nature Materials             <\/em>Volumen:<\/strong> 13                       Pag.:<\/strong> 382<\/em><\/p>\n\n\n\n

Abstract<\/strong>: Modern telecommunications\nrely on the transmission and manipulation of optical signals. Optical\namplification plays a vital part in this technology, as all components in a\nreal telecommunications system produce some loss. The two main issues with\npresent amplifiers, which rely on erbium ions in a glass matrix, are the\ndifficulty in integration onto a single substrate and the need of high pump\npower densities to produce gain. Here we show a potential organic optical\namplifier material that demonstrates population inversion when pumped from\nabove using low-power visible light. This system is integrated into an organic\nlight-emitting diode demonstrating that electrical pumping can be achieved.\nThis opens the possibility of direct electrically driven optical amplifiers and\noptical circuits. Our results provide an alternative approach to producing\nlow-cost integrated optics that is compatible with existing silicon photonics\nand a different route to an effective integrated optics technology.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Variation of the Cl-Fe3+<\/sup> charge-transfer energy with the Fe-Cl bond distance in [(CH3<\/sub>)4<\/sub>N]GaCl4<\/sub> doped with Fe3+<\/sup><\/summary>
\n

Author<\/strong>(s):  <\/strong>P. E.\nLizcano-Amorocho, J. A. Barreda-Arg\u00fceso,\nF. Aguado, R. Valiente, J. Gonz\u00e1lez and F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> 5<\/strong>2nd EHPRG Meeting, Lyon, France, 7-12 September\n2014<\/strong><\/p>\n\n\n\n

Abstract<\/strong>: Mixed organic\/inorganic crystals as [(CH3)4N]FeCl4 (Ref. 1)are receiving\nconsiderable attention due to their simple structure consisting of organic (CH3)4N+ and inorganic\nFeCl4–<\/sup> tetrahedra, being\nprecursors of magnetic ionic liquids having\nthe FeCl4 –<\/sup> as the\nmost common anion.2 The incorporation of magnetic anions as FeCl4 –<\/sup>\nmakes it attractive for modifying their thermodynamic properties by applying external\nmagnetic fields or illumination.3 In spite of its relevance the\nvibrational and electronic structures of FeCl4 – anions remain yet unexplored\nin part due to the scarce\nnumber of mixed organic\/inorganic crystals incorporating FeCl4 –<\/sup>\nanions in the structure, and the strong absorption of these materials in the visible-ultraviolet range, due to\nlowlying, spin and parity allowed electric-dipole chargetransfer transitions, forming the material band gap. Furthermore, these materials can be easily compressed due to the small\nbulk modulus (K <\/em>= 10\nGPa) in comparison to the local bulk\nmoduli of both organic and inorganic tetrahedra, being more than an order\nof magnitude higher. This work reports\ninvestigations on the structure, vibrational and electronic structures of [(CH3)4N]FeCl4 as a function\nof pressure with the aim of determining\nthe compression mechanisms governing the bulk and tetrahedra.\nThe charge-transfer electronic structure of FeCl4 – (Ref.\n4) has been investigated in\nthe Fe3+-diluted isomorphous material [(CH3)4N]GaCl4. We\nreport on the existence of this compound as well as on its\ncrystal, vibrational and electronic characterization under high-pressure conditions. The charge-transfer spectrum of this compound via\ndoping control (Figure 1) allowed us\nto report first investigation on the variation\nof the four charge-transfer bands with pressure and correlate them with the bond length\nvariation derived from Raman spectroscopy.\nA full report on the structure of these compounds and their associated properties will be presented at the conference.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure dependence of Raman modes in Graphene Oxide (GO) with water as pressure transmitting medium: an example of auxetic material \u00a0<\/summary>
\n

Author<\/strong>(s):  <\/strong>J. Gonz\u00e1lez, F. Rodr\u00edguez,\nR. Valiente<\/p>\n\n\n\n

Source:<\/strong> 5<\/strong>2nd EHPRG Meeting, Lyon, France, 7-12 September\n2014<\/strong><\/p>\n\n\n\n

Abstract<\/strong>: GO is a water-soluble nanomaterial prepared through extensive chemical attack of graphite crystals to introduce oxygen-containing defects in the graphite stack. In GO, a large fraction (0.5\u20130.6) of carbon\nis sp3<\/sup> hybridized and covalently bonded with oxygen in form of epoxy and hydroxyl groups. The remaining carbon\nis sp2<\/sup> hybridized and bonded either with\nneighboring carbon atoms or with\noxygen in the form of carboxyl and carbonyl groups, which predominantly decorate the edges\nof the graphene sheets. GO is therefore\na 2D network of sp2<\/sup>–\nand sp3<\/sup>-bonded atoms, in contrast\nto an ideal graphene sheet, which consists of 100% sp2<\/sup>-hybridized carbon atoms. This\nunique atomic and electronic structure of GO, consisting of variable sp2<\/sup>\/sp3<\/sup> fractions, opens up possibilities(channels\/ways) for new functionalities.\nThe most notable difference between GO and mechanically exfoliated graphene is the\noptoelectronic properties arising from the\npresence of a finite band\ngap [1]. In this work we have used a solution of GO prepared by GRAnPH Nanotech (Spain). The samples\nare characterized by high resolution transmission electronic microscopy, photoluminescence and\nRaman spectroscopy. In the Raman spectrum\nof graphene oxide the G\nband is broadened and shifted to 1594 cm-1<\/sup> whereas the D band at 1363 cm-1<\/sup>\nbecomes the prominent feature in the spectrum indicating\nthe creation of sp3<\/sup> domains due to the\nextensive oxidation. The intensity ratio of the D and G bands is a measure of the disorder, as expressed by the\nsp2<\/sup>\/sp3<\/sup> carbon ratio. In order to investigate their structural stability, unpolarized room temperature Raman spectra excited\nwith 514 nm were studied at high pressures. Typical diamond anvils used in high pressure experiments\nhave been substituted by moissanite (6H-SiC) and sapphire anvils to allow\nthe observation of the D band (around 1360 cm-1<\/sup>)\nand the second-order Raman scattering without interference [1]. Up to 15 GPa under paraffin\nwe found a pressure coefficient of 6.2 cm-1<\/sup>GPa-1<\/sup>\nfor the tangential\nG band and 4.1 cm-1<\/sup> GPa-1<\/sup> for the D band. The unit-cell volume of graphite oxide (GO) pressurized\nin the presence of water continuously increases, reaching a maximum at 1.3\u20131.5 GPa. The unit-cell volume of graphite oxide (GO) pressurized in the presence of water continuously increases, reaching a maximum at\n1.3\u20131.5 GPa [1]. Expansion of the lattice by 28\u201330% significantly exceeds all previously known examples and is due to\ngradual pressure induced water insertion into the interlayer\nspace of graphene oxide structure. Up to 4 GPa our Raman\nmeasurements, using water as the pressure\ntransmitting medium, show an anomaly in the\nvariation of the frequency of the G band with pressure which\nwe attribute to the insertion of water\nbetween the layers of the structure\nof GO. For pressures\nbetween 4 and 22 GPa the compressibility of GO is positive again and the pressure coefficient\nof the G band is 5 cm-1<\/sup>GPa-1<\/sup>. A large\nnumber of experimental and theoretical\nstudies have been published on the phase\ntransitions of confined water [2] which are considerably different from those of bulk\nwater.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Interplay between spin state and Jahn-Teller effect in transition metal systems<\/summary>
\n

Author<\/strong>(s): <\/strong>F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Lule\u00e5 University of Technology    <\/strong>Lule\u00e5(Sweden)\n                                   June\n(2014)<\/p>\n\n\n\n

Abstract<\/strong>: The optical, electrical and magnetic properties of\ntransition-metal-ion (TM<\/em>) compounds\nstrongly depend on the ground-state spin. In oxides and halides containing Mn3+<\/sup>(3d4<\/sup>);\nNi3+<\/sup>(3d7<\/sup>), Co3+<\/sup>(3d6<\/sup>), or Co2+<\/sup>(3d7<\/sup>),\nthe electronic ground state is close to the spin crossover transition and\nsubtle structural distortions around the TM<\/em>\ndue to the Jahn-Teller effect occurring at either the\nlow spin (LS) or high-spin (HS) state may favour stabilization of either a LS\nor a HS ground state upon compression. The prediction of which spin state will\nbe stable at given conditions of pressure and temperature is not easy,\nparticularly, in sixfold coordinated TM<\/em> compounds where the Jahn-Teller effect can play a crucial role. In most cases\ntheir structural characterization is hard to accomplish through diffraction\ntechniques due to topological disorder induced by dynamics or spin state mixing\nand thus adequate structural\ncharacterization<\/em> often deserves using complementary techniques. <\/em>In this talk a high-pressure spectroscopy study to explore the spin state and associated structural distortions in TM ions undergoing spin crossover transitions induced by pressure is\npresented. In particular, we\napply this technique for investigating\nspin crossover phenomena in Jahn-Teller\nsystems of Mn3+<\/sup>, Co3+<\/sup>. The possible involvement\nof the intermediate spin\n(IS) state in the spin\ncrossover in Co3+<\/sup> will be discussed in connection with high-pressure experiments carried out in the isoelectronic\nFe2+<\/sup> in (Mg,Fe)O and its\ngeophysical implications. Also diffraction and spectroscopic techniques under high-pressure conditions in the charge-transfer compound CoCl2<\/sub>\nwill be presented to analyze the\nrelationship between spin transition and metallization<\/p>\n<\/div><\/details><\/div>\n\n\n\n

2013<\/strong><\/p>\n\n\n\n

The effects of hydrostatic pressure on matrix-free germanium quantum dots<\/em><\/summary>
\n

Author<\/strong>(s): <\/strong>W. Little, A. Karakoulu, I.Hernandez, F. Rodriguez, J.A. Gonzalez, D. Dunstan and A. Sapelkin<\/p>\n\n\n\n

Source:<\/strong> <\/em>European\nHigh Pressure Research Group International Meeting (EHPRG51).-\n1-6- Septiembre 2013, Queen Mary, University\nof London, UK<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Experimental and theoretical pressure coefficients for the RBM, G-plus and G-minus Raman modes of carb\u00f3n<\/em><\/summary>
\n

Author<\/strong>(s): <\/strong>Y. Sun,\nJ.E. Proctor, M. Halsall,\nI.F. Crowe, A. Sapelkin,\nIgnacio Hernandez, F. Rodriguez,\nJ.A. Gonzalez y D. Dunstan  <\/p>\n\n\n\n

Source:<\/strong> <\/em>European High Pressure Research Group International Meeting (EHPRG51)         Queen Mary, University of London, UK<\/p>\n<\/div><\/details><\/div>\n\n\n\n

POSTER \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 EHPRG \u00a0\u00a0\u00a0\u00a0\u00a0LONDON: \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Pressure impact on the stability and distortion of \u00a0the crystal structure and lattice vibrations of \u00a0CeScO3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>D. Errandonea, F. Aguado, J. Gonzalez, J.A. Barreda, O. Gomis,\nD. Santamaria-Perez, B. Garcia-Domene,\nD. Martinez-Garcia, R. Shukla,\nS.N. Achary, A.K. Tyagi,\nand. C. Popescu<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.88.214108 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence in ZnO:Co2+<\/sup> (0.01%\u20135%) Nanoparticles, Nanowires, Thin Films, and Single Crystals as a Function of Pressure and Temperature: Exploring Electron\u2013Phonon Interactions<\/summary>
\n

Author(s): <\/strong>Carlos Renero-Lecuna<\/a>, Rosa Mart\u00edn-Rodr\u00edguez<\/a>, Jesus A. Gonz\u00e1lez<\/a>, Fernando Rodr\u00edguez<\/a>, Gloria Almonacid<\/a>, Alfredo Segura<\/a>, Vicente Mu\u00f1oz-Sanjos\u00e9<\/a>, Daniel R. Gamelin<\/a> and Rafael Valiente<\/a> <\/strong><\/p>\n\n\n\n

Source:<\/strong> American Chemical\nSociety    Volume:<\/strong>  108                       Pagina:<\/strong> 166402<\/strong><\/p>\n\n\n\n

Abstract<\/strong>: This work investigates the\nelectronic structure and photoluminescence properties of Co2+<\/sup>-doped\nZnO and their pressure and temperature dependences through high-resolution\nabsorption and emission spectroscopy as a function of Co2+<\/sup>\nconcentration and their structural conformations as a single crystal, thin\nfilm, nanowire, and nanoparticle. Absorption and emission spectra of diluted\nZnO: Co2+<\/sup> (0.01 mol %) can be related to the 4<\/sup>T1<\/sub>(P)\n\u2192 4<\/sup>A2<\/sub>(F) transition of CoO4 <\/sub>(Td),\ncontrary to MgAl2O4<\/sub>:Co2+<\/sup> and ZnAl2<\/sub>O4<\/sub>:Co2+<\/sup>\nspinels in which the red emission is ascribed to the 2<\/sup>E(G) \u2192 4<\/sup>A2<\/sub>(F)\ntransition. We show that the low-temperature emission band consists of a 4T1<\/sub>(P)\nzero-phonon line and a phonon-sideband, which is described in terms of the\nphonon density of states within an intermediate coupling scheme (S = 1.35)\ninvolving all ZnO lattice phonons. Increasing pressure to the sample shifts the\nzero-phonon line to higher energy as expected for the 4<\/sup>T1<\/sub>(P)\nstate upon compression. The low-temperature emission quenches above 5 GPa as a\nconsequence of the pressure-induced wurtzite to rock-salt structural phase\ntransition, yielding a change of Co2+<\/sup> coordination from 4-fold Td to\n6-fold Oh . We also show that the optical properties of ZnO:Co2+<\/sup>\n(Td) are similar, independent of the structural conformation of the host and\nthe cobalt concentration. The Co2+<\/sup> enters into regular Zn2+<\/sup>\nsites in low concentration systems (less than 5% of Co2+<\/sup>), although\nsome slight shifts and peak broadening appear as the dimensionality of the\nsample decreases. These structural effects on the optical spectra are also\nsupported by Raman spectroscopy.<\/p>\n\n\n\n

DOI: <\/strong>10.1021\/cm403371n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Multiwalled Carbon Nanotubes Hinder Microglia Function Interfering with Cell Migration and Phagocytosis<\/summary>
\n

Author(s): <\/strong>Juan C. Villegas, Laura\n\u00c1lvarez-Montes, Lidia Rodr\u00edguez-Fern\u00e1ndez, Jes\u00fas Gonz\u00e1lez, Rafael Valiente and\nM\u00f3nica L. Fanarraga<\/p>\n\n\n\n

Source:<\/strong> <\/em>Adanced. Healthcare Mater       <\/strong><\/p>\n\n\n\n

Abstract<\/strong>: The intranasal drug delivery\nroute provides exciting expectations regarding the application of engineered\nnanomaterials as nano-medicines or drugdelivery vectors into the brain. Among\nnanomaterials, multiwalled CNTs (MWCNTs) are some of the best candidates for\nbrain cancer therapy since they are well known to go across cellular barriers\nand display an intrinsic ability to block cancer cell proliferation triggering\napoptosis. This study reveals that microglial cells, the brain macrophages and\nputative vehicles for MWCNTs into the brain, undergo a dose-dependent cell\ndivision arrest and apoptosis when treated with MWCNTs. Moreover, it is shown\nthat MWCNTs severely interfere with both cell migration and phagocytosis in live\nmicroglia. These results lead to a re-evaluation of the safety of inhaled\nairborne CNTs and provide strategic clues of how to biocompatibilize MWCNTs to\nreduce brain macrophage damage and to develop new nanodrugs. <\/p>\n\n\n\n

DOI:\n<\/strong>10.1002\/adhm.201300178<\/p>\n<\/div><\/details><\/div>\n\n\n\n

3D Raman mapping of uniaxially loaded 6H-SiC crystals<\/summary>
\n

Author<\/strong>(s): <\/strong>E. del Corro, J. G. Izquierdo, J. Gonz\u00e1lez, M. Taravillo and V. G. Baonza<\/p>\n\n\n\n

Source:<\/strong> <\/em>Journal of Raman Spectroscopy           <\/strong><\/p>\n\n\n\n

Abstract<\/strong>: Raman spectroscopy is used to investigate\nthe three-dimensional stress distribution in 6H-silicon carbide (SiC) specimens subjected to stresses up to 3.7GPa along the\nc-axis. Specifically, the relative Raman shift of the longitudinal optic phonon\nof 6H-SiC is used to evaluate the local stress across the bulk crystal. For\nthis purpose, an anvil device with opposed 6H-SiC and sapphire specimens was\nused. After subjecting the anvils to uniaxial load,\nseveral series of two-dimensional Raman maps were registered at different\ndepths in the 6H-SiC anvil. The analysis of the Raman spectra reveals an\nexponential decay of the stress as a function of the depth. A novel\nphenomenological Gr\u00fcneisen-like model is introduced\nhere to account for such observation. On the contrary, the in-plane stress analysis\nshows a radial Gaussian-like distribution regardless the depth, a distinct\nbehavior that is attributed to the appearance of shear stress components. The\nsuitability of both models and their applicability to other materials are\ndiscussed, along with some future directions. <\/p>\n\n\n\n

Keywords<\/strong>: silicon carbide; strain\ndistribution; 3D imaging; moissanite anvil; shear and\nin-plane stresses<\/p>\n\n\n\n

DOI: <\/strong>10.1002\/jrs.4252<\/p>\n<\/div><\/details><\/div>\n\n\n\n

A Magnetic Ionic Liquid Based on Tetrachloroferrate Exhibits Three-Dimensional Magnetic Ordering: A Combined Experimental and Theoretical Study of the Magnetic Interaction Mechanism<\/summary>
\n

Author<\/strong>(s): <\/strong>Abel Garc\u00eda-Saiz, Pedro Migowski,\nOriol Vallcorba, Javier Junquera, Jes\u00fas Angel Blanco, Jes\u00fas Antonio Gonz\u00e1lez, Mar\u00eda Teresa\nFern\u00e1ndez-D\u00edaz, Jordi Rius, Jairton\nDupont, Jes\u00fas Rodr\u00edguez Fern\u00e1ndez and Imanol de Pedro<\/p>\n\n\n\n

Source:<\/strong> <\/em>Chemistry a European Journal Communication         <\/p>\n\n\n\n

Vol.:<\/strong> 20         Pag<\/strong>.:<\/strong> 72\u201376<\/strong><\/p>\n\n\n\n

Abstract<\/strong>: A new magnetic ionic liquid (MIL)\nwith 3D antiferromagnetic ordering has been synthetized and characterized. The information obtained\nfrom magnetic characterization was supplemented by analysis of DFT calculations\nand the magneto-structural correlations. The result gives no evidence for\ndirect iron-iron interactions, corroborating that the 3D magnetic ordering in\nMILs takes place via super-exchange coupling containing two diamagnetic atoms\nintermediaries.<\/p>\n\n\n\n

Keywords<\/strong>: density functional calculations,\nionic liquids, magnetic properties, structure elucidation<\/p>\n\n\n\n

DOI: <\/strong>10.1002\/chem.201303602<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Ab Initio Study of the Electronic and Vibrational Properties of 1-nm-Diameter Single-Walled Nanotubes<\/summary>
\n

Author(s): <\/strong>Jes\u00fas Marquina, Chrystian Power, Jes\u00fas Gonz\u00e1lez, Jean-Marc Broto<\/p>\n\n\n\n

Source:<\/strong> <\/em>Advances in Materials Physics and Chemistry           <\/p>\n\n\n\n

Vol.:<\/strong> 3            Pag<\/strong>.:<\/strong> 178-184<\/strong><\/p>\n\n\n\n

Abstract<\/strong>: The electronic structure, band gap,\ndensity of states of the (8,8), (14,0) and (12,3) single-walled carbon nanotubes by the SIESTA (Spanish Initiative for Electronic\nSimulations with Thousands of Atoms) method in the framework den-sity-functional theory (DFT) with the generalized gradients\napproximation (GGA) were studied. Also, we studied the vibrational\nproperties of the (8,8) and (14,0) nanotubes.\nOnly the calculated relaxed geometry for (12,3) nanotube show significant deviations from the ideal rolled graphene sheet configuration. The electronic transition\nenergies of van Hove singularities were studied and compared with previous\nresults. The calculated band structures, density of states and dis-persion curves for all tubes were in good agreement\nwith theoretical and experimental results. <\/p>\n\n\n\n

Keywords<\/strong>: Carbon Nanotubes;\nElectronic Structure; Dispersion Curve<\/p>\n\n\n\n

DOI: <\/strong>10.4236\/ampc.2013.32025<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure dependence of Raman modes in Graphene Oxide (GO)<\/summary>
\n

Author(s): <\/strong>Jes\u00fas Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong>\n<\/em>NanoSpain2013  (ORAL)  205-206<\/em><\/p>\n\n\n\n

Abstract<\/strong>: GO is a water-soluble nanomaterial prepared through extensive chemical attack of\ngraphite crystals to introduce oxygen-containing defects in the graphite stack.\nIn GO, a large fraction (0.5\u20130.6) of carbon is sp3 hybridized and covalently\nbonded with oxygen in form of epoxy and hydroxyl groups. The remaining carbon is\nsp2 hybridized and bonded either with neighboring carbon atoms or with oxygen\nin the form of carboxyl and carbonyl groups, which predominantly decorate the\nedges of the graphene sheets. GO is therefore a 2D\nnetwork of sp2 and sp3-bonded \natoms, in contrast to an ideal graphene\nsheet, which consists of 100% sp2-hybridized carbon atoms. This unique atomic\nand electronic structure of GO, consisting of variable sp2\/sp3 fractions, opens\nup possibilities for new functionalities. The most notable difference between\nGO and mechanically exfoliated graphene is the\noptoelectronic properties arising from the presence of a finite band gap [1].\nIn this work we have used a solution of GO prepared by GRAnPH\nNanotech (Spain). The samples are characterized by high resolution transmission\nelectronic microscopy, photoluminescence and Raman spectroscopy. In the Raman\nspectrum of graphene oxide the G band is broadened\nand shifted to 1594 cm-1 whereas the D band at 1363 cm-1 becomes the prominent\nfeature in the spectrum indicating the creation of sp3 domains due to the\nextensive oxidation (see figure 1). The intensity ratio of the D and G bands is\na measure of the disorder, as expressed by the sp2\/sp3 carbon ratio. In order\nto investigate their structural stability unpolarized\nroom temperature Raman spectra excited with 514 nm were studied at high\npressures. Typical diamond anvils used in high pressure experiments have been\nsubstituted by moissanite (6H-SiC) anvils to allow\nthe observation of the D band (around 1360 cm -1) and the second-order Raman\nscattering without interference [2] (figure 2). Up to 15 GPa we found a pressure coefficient of 6.2 cm-1 GPa-1\nfor the tangential G band and 4.1 cm-1 GPa-1 for the D band (figure 3). No\npressure-induced structural phase transition was observed in the studied\npressure range.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced phase-transition sequence in CoF2: An experimental and first-principles study on the crystal, vibrational, and electronic properties<\/summary>
\n

Author<\/strong>(s): <\/strong>J. A. Barreda-Arg\u00fceso, S. L\u00f3pez-Moreno, M. N. Sanz-Ortiz,\nF. Aguado, R. Valiente, J. Gonz\u00e1lez, F. Rodr\u00edguez, A. H. Romero, A. Mu\u00f1oz, L.\nNataf, and F. Baudelet<\/p>\n\n\n\n

Source:<\/strong>\n<\/em>PHYSICAL REVIEW B                           Vol.:<\/strong>    88                  Pag<\/strong>.:<\/strong>  214108<\/em><\/p>\n\n\n\n

Abstract<\/strong>: We report a complete structural\nstudy of CoF2<\/sub> under pressure. Its crystal structure and vibrational and electronic properties have been studied\nboth theoretically and experimentally using first- principles density\nfunctional theory (DFT) methods, x-ray diffraction, x-ray absorption at Co\nK-edge experiments, Raman spectroscopy, and optical absorption in the 0\u201380 GPa range.We have determined the\nstructural phase-transition sequence in CoF2<\/sub> and corresponding\ntransition pressures. The results are similar to other transition-metal difluorides such as FeF2<\/sub> but different to ZnF2<\/sub>\nandMgF2<\/sub>, despite that theCo2+<\/sup> size (ionic radius) is\nsimilar to Zn2+<\/sup> andMg2+.<\/sup>We found that the complete\nphase-transition sequence is tetragonal rutile (P42\/mnm)\u2192CaCl2<\/sub> type (orthorhombic Pnnm)\u2192distorted PdF2<\/sub> (orthorhombic Pbca)+PdF2<\/sub> (cubic Pa3\u00b4) in coexistence\u2192fluorite\n(cubic Fm3\u00b4m)\u2192cotunnite (orthorhombic Pnma). It was observed that the structural phase transition\nto the fluorite at 15 GPa involves a drastic change\nof coordination from sixfold octahedral to eightfold\ncubic with important modifications in the vibrational\nand electronic properties.We show that the\nstabilization of this high-pressure cubic phase is possible under nonhydrostatic conditions since ideal hydrostaticity\nwould stabilize the distorted-fluorite structure (tetragonal I4\/mmm) instead. Although the first rutile\u2192CaCl2<\/sub>-type\nsecond-order phase transition is subtle by Raman spectroscopy, it was possible\nto define it through the broadening of the Eg Raman\nmode which is split in the CaCl2<\/sub>-type phase. First-principles DFT\ncalculations are in fair agreement with the experimental Raman mode\nfrequencies, thus providing an accurate description for all vibrational\nmodes and elastic properties of CoF2<\/sub> as a function of pressure.<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.88.214108<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Magnetic ionic plastic crystal: choline[FeCl4<\/sub>]<\/summary>
\n

Author(s): <\/strong>I. de Pedro, A. Garc\u00eda-Saiz, J.\nGonz\u00e1lez, I. Ruiz de Larramendi, T. Rojo, Carlos A. M. Afonso, Svilen P.\nSimeonov, J. C. Waerenborgh, Jes\u00fas A. Blanco,B. Ramajog and J. Rodr\u00edguez\nFern\u00e1ndez<\/p>\n\n\n\n

Source:<\/strong>\n<\/em>Physical. Chemistry         Vol.:<\/strong>    15                  Pag.:<\/strong> \n12724–12733<\/em><\/p>\n\n\n\n

Abstract<\/strong>: A novel organic ionic plastic\ncrystal (OIPC) based on a quaternary ammonium cation and a tetrachloroferrate\nanion has been synthesized with the intention of combining the properties of\nthe ionic plastic crystal and the magnetism originating from the iron\nincorporated in the anion. The thermal analysis of the obtained OIPC showed a\nsolid\u2013solid phase transition below room temperature and a high melting point\nabove 220 1C, indicating their plastic crystalline behaviour over a wide\ntemperature range, as well as thermal stability up to approximately 200 1C. The\nmagnetization measurements show the presence of three-dimensional\nantiferromagnetic ordering below 4 K. The results from electrochemical characterization\ndisplay a solid-state ionic conduction sufficiently high and stable (between\n10_2.7 and 10_3.6 S cm_1 from 20 to 180 1C) for electrochemical applications.<\/p>\n\n\n\n

DOI<\/strong>: 10.1039\/c3cp50749a<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure studies of topological insulators Bi2<\/sub>Se3<\/sub>, Bi2<\/sub>Te3<\/sub>, and Sb2<\/sub>Te3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>F. J. Manj\u00f3n, R. Vilaplana, O. Gomis, E.\nP\u00e9rez-Gonz\u00e1lez, D. Santamar\u0131\u00eda-P\u00e9rez, V. Mar\u00edn-Borr\u00e1s, A. Segura, J. Gonz\u00e1lez, P. Rodr\u00edguez-Hern\u00e1ndez, A.\nMu\u00f1oz, C. Drasar, V. Kucek,\nand V. Mu\u00f1oz-Sanjose<\/p>\n\n\n\n

Source:<\/strong>\n<\/em>Physical Status Solidi B             Vol.:<\/strong>   \n250, 488                   Pag<\/strong>.:<\/strong>  669\u2013676<\/em><\/p>\n\n\n\n

Abstract<\/strong>: Bi2<\/sub>Se3<\/sub>, Bi2<\/sub>Te3<\/sub>,\nand Sb2<\/sub>Te3<\/sub> are narrow bandgap\nsemiconductors with tetradymite crystal structure\n(R-3m) which have been extensively studied along with their alloys due to their\npromising operation as thermoelectric materials in the temperature range\nbetween 300 and 500 K. Studies on these layered semiconductors have increased\ntremendously in the last years since they have been recently predicted and demonstrated\nto behave as 3D topological insulators. In particular, a number of\nhigh-pressure studies have been done in the recent years in these materials. In\nthis work we summarize the main results of the high-pressure studies performed\nin this family of semiconductors to date. In particular, we review recent\nresults that address the main characteristics of the pressure-induced\nelectronic topological transition and structural phase transitions observed in\nthis family of compounds. Future high-pressure studies to be performed on these\n3D topological insulators are also commented<\/p>\n\n\n\n

Keywords: <\/strong> Bi2<\/sub>Se3<\/sub>,\nBi2<\/sub>Te3<\/sub>, high pressure, Sb2<\/sub>Te3<\/sub>,\ntopological insulators<\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/pssb.201200672<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Synthesis of porous clay heterostructures from highcharge mica-type aluminosilicates<\/summary>
\n

Author<\/strong>(s): <\/strong>Ana C. Perdig\u00f3n, Defeng Li,\nCarmen Pesquera, Fernando Gonz\u00e1lez, Bel\u00e9n Ortiz, Fernando Aguado and Carmen\nBlanco<\/p>\n\n\n\n

Source:<\/strong> <\/em>Journal of Materials Chemistry A                      Vol.:<\/strong>    1                    Pag<\/strong>.:<\/strong>  1213<\/p>\n\n\n\n

Abstract<\/strong>: High charge micas are ideal\nmaterials to be used as porous solid acids because of their extraordinarily\nhigh content of framework aluminium atoms and their\nthermal stability. However, all efforts to reate\nporosity in these materials have led to a disordered porous structure, since\nthe full process is compromised by the highly layer attractive forces and hence\nby the incorporation stage of the porous wall precursors between the clay\nlayers. Thermally stable and ordered mesoporous\nmaterials were synthesized for the first time from those swelling brittle micas\nthrough a surfactant templating approach. The\ninterlayer space was firstly preexpanded using alkylammonium cations, giving\nrise to a homogeneous organic\u2013inorganic hybrid structure, which directs the\npolymerization step of the silica source. A regular porous structure in the supermicropore to the small mesopore\nrange (15\u201325 \u00b0A) together with an exclusive acidity was found after sample calcination. The extraordinary content of framework aluminium is responsible for the large number of acid\nsites, both in the rare medium and strongly acidic regions. The thermal\nstability of the new synthesised materials was also\ntested.<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/c2ta00543c<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Crystal-field dependence with Co2+<\/sup>-F–<\/sup> distance in the perovskite KCoF3<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>J.A. Barreda Arg\u00fceso,F.\nAguado, F. Rodr\u00edguez, S.A.T. Redfern<\/p>\n\n\n\n

Source:\n<\/strong> <\/em>AIRAPT’13,\nSeattle, EEUU, 2013                   Vol.:<\/strong>   \n                       Pag<\/strong>.:<\/strong>  <\/p>\n\n\n\n

Abstract<\/strong>: Perovskite crystals\nare attractive for structural studies at high pressure in a wide\nmultidisciplinary science. Perovskite or distorted-perovskite oxides are relevant as solid state devices as\nmany of them exhibit properties such as colossal magnetoresistance,\nexotic magnetism, or even high TC<\/sub> superconductivity. In geoscience, the understanding of high-pressure posperovskite phase is noteworthy. In this sense, it must\nbe noted that NaCoF3<\/sub> transforms to the postperovskite\nphase at a moderate pressure (P =<\/em> 15 GPa) in comparison to oxides [1].\nHowever KCoF3<\/sub> seems to lack this transition as it remains in the perovskite structure up to higher pressure [2]. This\nwork reports a structural study in KCoF3<\/sub> as a function of pressure\nin the 0-60 GPa range. Its\nlarge pressure perovskite stability is noteworthy.\nTherefore, this is a unique system to establish correlations between crystal\nand electronic structures in a high-symmetry phase, where Co2+<\/sup> ions\nare located in a perfect octahedral environment. Here we present an x-ray\ndiffraction study in correlation with single-crystal optical absorption\nspectroscopy. The variation of the crystal-field strength and Racah parameters of Co2+<\/sup> with the crystal volume\n(and Co-F distance) up to 60 GPa\nare presented, discussed and compared with available data in other structures\ninvolving oxides and chlorides.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical Absorption and Raman Spectroscopy of CuGeO3<\/summary>
\n

Author<\/strong>(s): <\/strong>J.A. Barreda Arg\u00fceso,\nF. Aguado, R. Valiente, J. Gonz\u00e1lez, H.D. Hochheimer\nand F. Rodr\u00edguez<\/p>\n\n\n\n

Source:\n<\/strong> <\/em>EHPRG, London, UK, 2013                  Conferencia<\/strong>  <\/p>\n\n\n\n

Abstract<\/strong>: Copper metagermanate (CuGeO3<\/sub>)\nis a prototype of inorganic system exhibiting a spin-Peierls\ntransition at low temperature [1]. At room temperature CuGeO3<\/sub>\nbelongs to the orthorhombic (Pbmm<\/em>) [2-4], the unit cell containing two edge-sharing\nstrongly elongated CuO6<\/sub> octahedra as a\nresult of the combined Jahn-Teller effect and crystal\nanisotropy, with two-long and four-short Cu-O bonds of 2.77 and 1.94 \u00c5,\nrespectively [5,6]. They are coupled to form one-dimensional antiferromagnetic Cu-O chains along the c axis.  The band gap at about 3 eV\nand related optical and magnetic properties strongly depend on the structure of\nCuO6<\/sub> octahedra and how they are coupled in\nthe network of GeO4<\/sub> tetrahedra [4-5].\nDespite the importance of GeO4<\/sub> modulating the crystal structure of\nCuGeO3<\/sub>, the optical and magnetic properties are mainly governed by\nthe edge-linked CuO6<\/sub> octahedra [5].\nSimilarly to CuWO4<\/sub> [6], such properties are related to the\nelectronic structure of the strongly distorted CuO6<\/sub> octahedra, and the oxygen-mediated Cu-Cu exchange\ninteraction, which is modulated by both the distortion and octahedron tilting\n[6]. CuGeO3<\/sub> exhibits a rich structural phase-transition sequence\nwith pressure [4] which is subtly associated with the packing of CuO6<\/sub>\nand GeO4<\/sub> polyhedra upon compression, being\nstrongly dependent on the hydrostaticity of the\ntransmitting media.<\/p>\n\n\n\n

This work reports investigation on\nthe electronic and vibrational structure of CuGeO3<\/sub>\nby optical absorption and Raman spectroscopy as a function of pressure and\ntemperature. We aim to correlate variations of the band gap, d-d<\/em>\ntransitions associated with Cu2+<\/sup> and vibrational\nmode frequencies with corresponding changes of the crystal structure and\nparticularly of the local CuO6<\/sub> distortion and orientation. We\nconclude that Cu2+<\/sup> d<\/em>-orbital\nsplitting derived from absorption spectroscopy is consistent with the actual\nelongated distortion of the CuO6<\/sub> octahedron at ambient conditions.\nIts variation with pressure clearly reveals phase transition phenomena,\nproviding information on the CuO6 <\/sub>local structure. We show that\nhigh-pressure phases (IV-IV’) involve two different distorted CuO6<\/sub> octahedra, whereas in phase (V) CuO6<\/sub> exhibits a\nlarge non-centrosymmetric distortion, as suggested by\nthe increase of oscillator strength of the d-d<\/em>\ntransition by an order of magnitude. In addition, we study pressure-induced\nstructural transitions together with pressure variations of the GeO4<\/sub>\nmodes by Raman spectroscopy.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced Pr3+<\/sup>\u00a0 3<\/sup>Po luminescence in cubic Y2<\/sub>O3 <\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>Alok M. Srivastava, Carlos Renero-Lecuna,\nDavid Santamar\u00eda-P\u00e9rez, Fernando Rodr\u00edguez, Rafael Valiente<\/p>\n\n\n\n

Source:<\/strong> <\/em>Journal of Luminescence                       Vol.:<\/strong>   \n146                Pag<\/strong>.:<\/strong>  27-32<\/p>\n\n\n\n

Abstract<\/strong>: An explanation for the puzzling\nabsence of luminescence from the Pr3+<\/sup> 3<\/sup>P\u03c0=1,2 states in C-Ln2<\/sub>O3<\/sub> family of\nmaterials is provided by conducting a study of the emission properties of C-Y2<\/sub>O3<\/sub>:Pr3+\n<\/sup>under applied hydrostatic pressure. Above 7GPa, electronic transitions\nfrom the Pr3+<\/sup> 3<\/sup>P\u03c0=1,2\nstates are observed in the emission spectrum of C-Y2<\/sub>O3<\/sub>:Pr3+\n<\/sup>at room temperature and below. The experimental data reveal that the\ncrystal-field split Pr3+ 4<\/sup>f1<\/sub>5<\/sup>d1<\/sub> configuration\nis located entirely within the host lattice conduction band and that the\npromotion of the electron to the Pr3\u00fe 4f15d1 state produces a self-trapped exciton-like state with the configuration, [Pr4\u00fe\u00feeCB],\nwhere eCB<\/sub>indicates an electron\nin the host lattice conduction band. Upon excitation, the exciton-like\nstate by passes the upper emitting 3<\/sup>P\u03c0=1,2\nstates and directly feeds the lower emitting 1D2 state. This explains the\nabsence of optical transitions from the Pr3+<\/sup> 3<\/sup>P\u03c0=1,2 states intheemissionspectrumofC-Y2O3:Pr3\u00fe at ambient\npressure. At high pressures, emission transitions from the Pr3+<\/sup> 3<\/sup>P\u03c0=1,2  states are\nobserved because of the localization of the Pr3+ 4<\/sup>f1<\/sub>5<\/sup>d1<\/sub>  state to below the host lattice conduction\nband edge. <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2013.09.028<\/p>\n\n\n\n

Keywords:<\/strong> Cubic-Y2<\/sub>O3<\/sub> Pr3<\/sup>+,\nPhotoluminescence, High pressure, Self-trapped exciton<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Efficient sensitized emission in Yb(III) pentachlorotropolonate complexes<\/summary>
\n

Author(s): <\/strong>I. Hern\u00e1ndez,\nY-X. Zheng, M. Motevalli,\nR.H.C. Tan, W.P. Gillin and P.B. Wyatt<\/p>\n\n\n\n

Source:\n<\/strong>Chemistry\nCommunication                    Vol.:<\/strong>   \n49                  Pag<\/strong>.:<\/strong>  1933-1935<\/p>\n\n\n\n

Abstract<\/strong>: New Yb(III)\ncomplexes based on the pentachlorotropolonate (pctrop) ligand show enhanced\ninfrared emission when excited in the orange organic chromophore.\nYb(pctrop)3<\/sub>(DMF-d<\/em>7<\/sub>)2<\/sub>\npresents the highest reported quantum yield for a nonfluorinated\ninfrared-emitting organolanthanide complex.<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/C3CC38610D<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet<\/summary>
\n

Author(s): <\/strong>A. J. Ghandour,\nI. F. Crowe, J. E. Proctor, Y. W. Sun, M. P. Halsall,\nI. Hernandez, A. Sapelkin, and D. J. Dunstan<\/p>\n\n\n\n

Source:\n<\/strong>Physical Review B                      Vol.:<\/strong>    87                  Pag<\/strong>.:<\/strong>  085416<\/p>\n\n\n\n

Abstract<\/strong>: Studies\nof the mechanical properties of single-walled carbon nanotubes\nare hindered by their availability only as ensembles of tubes with a range of\ndiameters. However, tunable Raman spectroscopy is capable of identifying\nindividual tubes from such ensembles. Interestingly, both the radial breathing\nmode and, surprisingly, the G<\/em>-mode pressure coefficients exhibit strong\nenvironmental effects, which are largely independent of the nature of the\nenvironment. We show that the G<\/em>-mode pressure coefficient varies with\ndiameter, consistent with the thick-wall tube model. Reappraisal of literature\ndata for graphene and graphite suggests revision of\nboth the G<\/em>-mode Gr\u00fcneisen parameter \u03b3 and\nthe shear deformation parameter \u03b2 toward the value of 1.34.<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.87.085416<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Importance of Spin-Orbit Interaction for the Electron Spin Relaxation in Organic Semiconductors<\/summary>
\n

Author(s): <\/strong>L. Nuccio, M. Willis, L. Schulz, S.\nFratini, F. Messina, M. D\u2019Amico, F. L. Pratt, J. S. Lord, I. McKenzie, M. Loth,\nB. Purushothaman, J. Anthony, M. Heeney, R. M. Wilson, I. Hern\u00e1ndez, M. Cannas,\nK. Sedlak, T. Kreouzis, W. P. Gillin, C. Bernhard, and A. J. Drew<\/p>\n\n\n\n

Source:\n<\/strong>Physical Review\nLetters             Vol.:<\/strong>    110                Pag.:<\/strong>  216602<\/p>\n\n\n\n

Abstract<\/strong>: Despite\nthe great interest organic spintronics has recently attracted, there is only a\npartial understanding of the fundamental physics behind electron spin\nrelaxation in organic semiconductors. Mechanisms based on hyperfine interaction\nhave been demonstrated, but the role of the spin-orbit interaction remains\nelusive. Here, we report muon spin spectroscopy and time-resolved\nphotoluminescence measurements on two series of molecular semiconductors in\nwhich the strength of the spin-orbit interaction has been systematically\nmodified with a targeted chemical substitution of different atoms at a\nparticular molecular site. We find that the spin-orbit interaction is a\nsignificant source of electron spin relaxation in these materials.<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevLett.110.216602<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Effect of Fluorination on the Radiative Properties of Er3+<\/sup> Organic Complexes: An Opto-Structural Correlation Study<\/summary>
\n

Author(s): <\/strong>H. Ye, Y. Peng,\nZ. Li, C.-C. Wang, Y. Zheng, M. Motevalli , P.B. Wyatt ,\nW.P. Gillin and I. Hernandez<\/p>\n\n\n\n

Source:\n       <\/strong>Journal of Physical Chemistry C                Vol.:<\/strong>    117                Pag<\/strong>.:<\/strong>  23970\u201323975<\/p>\n\n\n\n

Abstract<\/strong>: It is\nexpected that fluorinated organic erbium(III)\ncomplexes, of interest for optical applications at \u03bb = 1.5 \u03bcm, have improved performance with respect to\nhydrogenated counterparts. However, the intrinsic radiative properties (including the absorption\/emission\nline strengths) of organic Er3+<\/sup> complexes have not been\nsystematically studied and compared up to date. This has precluded the\nobservation of opto-structural correlations as well\nas a proper characterization of the infrared f-f transitions and thus a lack of\nmeaningful figures for the optical efficiency of these materials at the 1.5 \u03bcm emission. We have performed a complete opto-structural correlation study of the oscillator\nstrengths of the f-f transitions of hydrogenated and fluorinated organic erbium(III) complexes, including a Judd-Ofelt\nanalysis. The Judd-Ofelt analysis on the crystals has\nallowed the study of the interdependence of the chemical nature, structure, and\nspectroscopic behavior. We observe clear trends that can help the design and\nunderstanding of these important infrared emitters for phosphor and opto-electronic applications.<\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/jp4093282<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence study of fluorinated organic semiconductors of the Zn(II) benzothiazole-phenoxide family at high pressure<\/summary>
\n

Author(s):\n<\/strong>I. Hern\u00e1ndez<\/p>\n\n\n\n

Source:\n<\/strong> <\/em>EHPRG 51, London, UK, 2013                        Vol.:<\/strong>                           Pag<\/strong>.:<\/strong>  <\/p>\n\n\n\n

Abstract<\/strong>: Organic semiconductors of the Zn(II) benzothiazole-phenoxide family have interesting\nspectroscopic properties, of interest towards electroluminescence and light\nharvesting. <\/p>\n\n\n\n

Structurally, while the hydrogenated compound shows a dimer structure, fluorinated species in which the phenoxide, the benzothiazole or\nboth groups are correspondingly tetra-fluorinated show centrosymmetric\ncrystal structures as arranged by the stacking interactions of the pi systems.\nThus, in this series of materials, depending on the chemical composition\ndifferent pi-H \u2013 pi-F or pi-F \u2013 pi-F stackings are\nachieved. <\/p>\n\n\n\n

Interestingly, apart from the purely molecular considerations governing\nthe HOMO and LUMO, pi-stacking plays an important role in stabilizing the\nmolecular states and has an influence in the absorption and emission energy.\nThus the emission wavelengths are redshifted in the\nsolid structure with respect to solutions and range from 491 nm (fluorinated in\nthe phenoxide ring) to 530 nm (fluorinated on the benzothiazole ring).<\/p>\n\n\n\n

Spectroscopic studies of complexes with different composition\n(fluorination) show that while the emission maximum experiences a variation of\n0.33 eV in the range 0-8 GPa\ncomplex fluorinated on the benzothiazole rings the\none partially fluorinated on the phenoxide rings\nexperiences Delta(Emax)=0.15 eV.\nThe perfluorinated material shows a value Delta(Emax)=0.22 eV in the same range. <\/p>\n\n\n\n

We will discuss the high pressure spectroscopic results and how they can\nhelp interpret the low pressure phenomenology.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Luminescent zinc(II) complexes of fluorinated benzothiazol-2-yl substituted phenoxide and enolate ligands<\/summary>
\n

Author(s):\n<\/strong>Z. Li, A. Dellali, J.\nMalik, M. Motevalli, R. M. Nix, T. Olukoya, Y. Peng, H. Ye, W. P. Gillin, I.\nHern\u00e1ndez and P. B. Wyatt<\/p>\n\n\n\n

Source:<\/strong> <\/em>Inorg. Chemistry               Vol.:<\/strong>   \n52                  Pag.:<\/strong> \n1379-1387<\/p>\n\n\n\n

Abstract<\/strong>: Fluorinated\nanalogs of the important dinuclear photo- and electroluminescent material\n[Zn(BTZ)2]2, where H-BTZ = 2-(2-hydroxyphenyl)benzothiazole, are found to be\nmononuclear. They easily sublime and show broad, bright visible\nphotoluminescence emission spectra. DFT calculations indicate that HOMO and\nLUMO energy levels in these materials are substantially lowered by\nfluorination.<\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/ic302063u<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2012<\/strong><\/p>\n\n\n\n

Effect of pressure on the band gap and the local FeO6<\/sub> environment in BiFeO3<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> Susana G\u00f3mez-Salces, Fernando Aguado, Fernando Rodr\u00edguez, Rafael Valiente, Jes\u00fas Gonz\u00e1lez, Raphael Haumont and Jens Kreisel<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B       Volume:<\/strong> 85          Pag<\/strong>: 144109<\/p>\n\n\n\n

Abstract:<\/strong> BiFeO3 exhibits a\ncomplex phase-transition sequence under pressure associated with changes in\noctahedron tilts and displacements of Bi3+\nand Fe3+ cations.\nHere, we investigate the local structure of Fe3+ as a function of pressure through\nabsorption crystal-field spectroscopy in the 0\u201318 GPa\nrange.We focus on the influence of phase transitions\non the Fe3+ off-center displacement through the energy (E<\/em>) and oscillator strength (f<\/em>d<\/em>\u2212d<\/em>) of the 4T1 and 4T2 Fe3+ (3d<\/em>5) bands observed below the band\ngap (E<\/em>gap = 2.49 eV) at 1.39 and 1.92 eV, respectively, at ambient conditions. Pressure induces\nlinear redshift of both 4T1 and 4T2 bands, consistent with the\ncompression of the FeO6 octahedron under pressure. On the other hand, the transition\noscillator strength (f<\/em>d<\/em>\u2212d\n<\/em>= 3 \u00d7 10\u22125), enabled by both the exchange\nmechanism and the off-center Fe3+\ndistortion, slightly increases\nwith pressure. The absence of notable anomalies in the variation of E<\/em>(P<\/em>) and f<\/em>d<\/em>\u2212d\n<\/em>(P<\/em>) through the phase sequence from the ferroelectric rhombohedral R<\/em>3c <\/em>phase to the nonpolar\northorhombic Pnma<\/em> <\/em>phase suggests a persisting off-center position of the\nFe3+. While this local polarity is correlated and expected\nin the ferroelectric R<\/em>3c\n<\/em>phase, its presence in the\nhigh-pressure nonpolar Pnma<\/em> <\/em>phase indicates the presence of\nlocal polar instabilities. <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.85.144109<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Multiwalled Carbon Nanotubes Display Microtubule Biomimetic Properties in Vivo, Enhancing Microtubule Assembly and Stabilization<\/summary>
\n

Author<\/strong>(s): <\/strong>Lidia Rodriguez-Fernandez, Rafael Valiente, Jes\u00fas\nGonz\u00e1lez, Juan C. Villegas and Monica L. Fanarraga<\/p>\n\n\n\n

Source: <\/strong>ACSNANO           Volume:<\/strong>    Pag<\/strong>.<\/strong>:  <\/p>\n\n\n\n

Abstract:<\/strong> Microtubules\nare hollow protein cylinders of 25 nm diameter which are implicated in cytokinetics and proliferation in all eukaryotic cells.\nHere we demonstrate in vivo how multiwalled carbon nanotubes (MWCNTs) interact with microtubules in human\ncancer cells (HeLa) blocking mitosis and leading to\ncell death by apoptosis. Our data suggest that, inside the cells, MWCNTs\ndisplay microtubule biomimetic properties, assisting\nand enhancing noncentrosomal microtubule\npolymerization and stabilization. These features might be useful for developing\na revolutionary generation of chemotherapeutic agents based on nanomaterials.<\/p>\n\n\n\n

DOI<\/strong>: Published online 10.1021\/nn302222m<\/p>\n\n\n\n

KEYWORDS:<\/strong> MWCNT. microtubules.\ncell division . HeLa cell. cancer. apoptosis<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure effects on Jahn-Teller distortion in perovskites: The roles of local and bulk compressibilitie<\/summary>
\n

Author<\/strong>(s): <\/strong>Fernando Aguado and Fernando Rodr\u00edguez, Rafael Valiente, Jean-Paul It\u00ede and Michael Hanfland<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B  RAPID COMUNICATIONS         Volume:<\/strong>  85   Pag.:  100101<\/p>\n\n\n\n

Abstract:<\/strong> The interplay between\nthe Jahn-Teller (JT) effect and octahedron tilting in\ntransition-metal perovskites is investigated as a\nfunction of pressure. Our focus is on its effects on the exchange and\nelectron-phonon interactions, both having a strong influence on materials\nproperties. We demonstrate that the JT distortion in Cu2+<\/sup> and Mn3+<\/sup>\nis reduced upon compression and is eventually suppressed at pressures above 20 GPa. X-ray diffraction and x-ray\nabsorption measurements in A<\/em>2<\/sub>CuCl4<\/sub> layer perovskites (A<\/em>: Rb, Cn<\/em>H2n+1<\/sub>NH3<\/sub>;\nn <\/em>= 1\u20133) show that, although pressure slightly reduces the long Cu-Cl distance in comparison to the Cu-Cu distance in the\nlayer, the JT distortion is stable in the 0\u201320 GPa\nrange. The difference between lattice (\u03b2C<\/em>0 = 0.<\/em>14 GPa\u22121<\/sup>) and local CuCl6<\/sub> (\u03b2<\/em>0\n= 0.<\/em>016 GPa\u22121) compressibilities,\ntogether with the high stability of the JT distortion, lead to CuCl6 tilts upon\ncompression. The evolution of the elongated CuCl6<\/sub> octahedron in A<\/em>2<\/sub>CuCl4,<\/sub>\nas well as MnF6<\/sub> in CsMnF4 and MnO6 <\/sub>in LaMnO3 <\/sub>and\nDyMnO3<\/sub>, toward a nearly regular octahedron takes place above 20 GPa, in agreement with experimental results and a model\nanalysis based on the JT energy derived from optical absorption spectroscopy: E<\/em>JT\n= 0.<\/em>25\u20130.45 eV\/<\/em>Cu2+, E<\/em>JT = 0.<\/em>45\neV\/<\/em>Mn3+<\/sup> (CsMnF4), and E<\/em>JT =\n0.<\/em>25 eV\/<\/em>Mn3+<\/sup> (LaMnO3<\/sub>).\nThe proposed model clarifies controversial results about pressure-induced JT\nquenching in Cu2+<\/sup> and Mn3+<\/sup> systems, providing an\nefficient complementary means to predict pressure behavior in perovskites containing JT transition-metal ions.<\/p>\n\n\n\n

DOI<\/strong>:  10.1103\/PhysRevB.85.100101<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced Co2+<\/sup> photoluminescence quenching in MgAl2<\/sub>O4<\/sub><\/summary>
\n

Author(s): <\/strong>Lucie Nataf and\nFernando Rodriguez and Rafael Valiente<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B  Volume:<\/strong>  86  Pag.:  125123<\/p>\n\n\n\n

Abstract:<\/strong> Coordination\nChemistry<\/p>\n\n\n\n

DOI<\/strong>:  10.1103\/PhysRevB.86.125123<\/p>\n\n\n\n

This work investigates the electronic structure and\nphotoluminescence (PL) of Co2+<\/sup>-doped MgAl2<\/sub>O4<\/sub> and\ntheir pressure dependence by time-resolved spectroscopy. The variations of the\nvisible absorption band and its associated emission at 663 nm (\u03c4 <\/em>= 130\nns at ambient conditions) with pressure\/temperature can be explained on the\nbasis of a configurational energy model. It provides\nan interpretation for both the electronic structure and the excited-state\nphenomena yielding photoluminescence emission and the subsequent quenching. We\nshow that there is an excited-state crossover (ESCO) [4T<\/em>1<\/sub>(P<\/em>)\n\u2194 2E<\/em>(G<\/em>)] at ambient pressure, which is responsible for the\nevolution of the emission spectrum from a broadband emission between 300 K and\n100 K to a narrow-line emission at lower temperatures. Contrary to expectations\nfrom the Tanabe-Sugano diagram, <\/strong>instead of enhancing ESCO phenomena,\npressure reduces PL and even suppresses it (PL quenching) above 6 GPa. We explain such variations in\nterms of pressure-induced nonradiative relaxation to\nlower excited states: 2E<\/em>(G<\/em>) \u2192 4T<\/em>1<\/sub>(F<\/em>).\nThe variation of PL intensity and its associated lifetime with pressure\nsupports the proposed interpretation. <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Reversibility of the zinc-blende to rock-salt phase transition in cadmium sulfide nanocrystals<\/summary>
\n

Author<\/strong>(s): <\/strong>R. Mart\u0131n-Rodr\u0131guez, J.\nGonzalez, R. Valiente, F. Aguado, D. Santamar\u0131a-Perez\nand F. Rodr\u0131guez<\/p>\n\n\n\n

Source: <\/strong>JOURNAL OF APPLIED\nPHYSICS Volume:<\/strong> 111   Pag<\/strong>.<\/strong>:  063516<\/p>\n\n\n\n

Abstract:<\/strong> CdS nanoparticles prepared by a mechanochemical reaction in a planetary ball mill have been\ninvestigated by x-ray diffraction, optical absorption, and Raman scattering\nunder high pressure conditions up to 11 GPa.\nThe zinc-blende (ZB) to rock-salt phase transition is\nobserved around 6 GPa in all experiments, the\ntransition pressure being similar to the one measured in CdS\ncolloidal nanocrystals, and much higher than in bulk\n(around 3 GPa). The direct optical energy gap in ZB-CdS increases with pressure, and suddenly drops when the\npressure is raised above 6 GPa,according\nto the high-pressure indirect-gap behavior. A linear blue-shift of the CdS Raman spectra is observed upon increasing pressure.\nBoth Raman and x-ray diffraction studies indicate that the phase transition has\na large hysteresis, making the ZB phase barely recoverable at ambient conditions.\nCell parameters and bulk modulus measured in CdS nanoparticles clearly show that the nanoparticles\nat ambient conditions are subject to an initial pressure in comparison to CdS bulk. <\/p>\n\n\n\n

DOI<\/strong>: dx.doi.org\/10.1063\/1.3697562<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Self-assembly of ultra-thin lanthanide oxide nanowires via surfactantmediated imperfect oriented attachment of nanoparticles<\/summary>
\n

Author(s): <\/strong>Fraser J. Douglas, Donald A. MacLaren,\nCarlos Renero-Lecuna, Robert D. Peacock,\nRafael Valiente and Mark Murrie<\/p>\n\n\n\n

Source:<\/strong> The Royal Society of\nChemistry           Volume:<\/strong>  14  Pag.:  7110\u20137114<\/p>\n\n\n\n

Abstract:<\/strong> We report a simple\nsynthesis of ultra-thin lanthanide oxide nanowires\nand ribbons via the autoclave-based decomposition of lanthanide oleates within passivating\nsurfactants. Electron microscopy reveals the formation of linear self\nassemblies of lanthanide oxide nanoparticles that\nsubsequently recrystallize into high aspect ratio\nmaterials via an \u2018\u2018imperfect oriented attachment\u2019\u2019 mechanism.<\/p>\n\n\n\n

DOI<\/strong>:  10.1039\/c2ce25990g<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Synthesis, structure and luminescence of Er3+<\/sup>-doped Y3<\/sub>Ga5<\/sub>O12 <\/sub>nano-garnets<\/summary>
\n

Author<\/strong>(s): <\/strong>Vemula Venkatramu, Sergio F. Le\u00f3n-Luis, Ulises R. Rodr\u00edguez-Mendoza,\nVirginia Monteseguro, Francisco J. Manj\u00f3n, Antonio D. Lozano-Gorr\u00edn,\nRafael Valiente, Daniel Navarro-Urrios, C. K. Jayasankar, Alfonso Mu\u00f1oz and V\u00edctor Lav\u00edn<\/p>\n\n\n\n

Source:<\/strong> Journal of Materials\nChemistry             Volume:<\/strong>  22   Pag.:  13788<\/p>\n\n\n\n

Abstract:<\/strong> A novel Y3(1_x)<\/sub>Er3x<\/sub>Ga5<\/sub>O12<\/sub>\nnanocrystalline garnet has been synthesized by a sol\u2013gel\ntechnique and a complete structural, morphological, vibrational,\nand optical characterization has been carried out in order to correlate the\nlocal structure of the Er3+ ions with their optical properties. The synthesized\nnanocrystals are found in a single-phase garnet\nstructure with an average grain size of around 60 nm. The good crystalline\nquality of the garnet structure is confirmed by FTIR and Raman measurements, since\nthe phonon modes of the nano-garnet are similar to\nthose found in the single crystal garnet. Under blue laser excitation, intense\ngreen and red visible and 1.5 mm infrared luminescences\nare observed, whose relative intensities are very sensitive to the Er3+ concentration.\nThe dynamics of these emissions under pulsed laser excitations are analyzed in\nthe framework of different energy transfer interactions. Intense visible upconverted luminescence can be clearly observed by the\nnaked eye for all synthesized Er3+<\/sup>-doped Y3<\/sub>Ga5<\/sub>O12<\/sub>\nnano-garnets under a cw 790\nnm laser excitation. The power dependency and the dynamics of the upconverted luminescence confirm the existence of different\ntwo-photon upconversion processes for the green and\nred emissions that strongly depend on the Er3+ concentration, showing the potential\nof these nano-garnets as excellent candidates for\ndeveloping new optical devices.<\/p>\n\n\n\n

DOI<\/strong>:  10.1039\/c2jm31386c<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2<\/sub>Se3 <\/sub>under high pressure<\/summary>
\n

Author<\/strong>(s): <\/strong>A. Segura, V. Panchal, J. F. Sanchez-Royo,\nV. Mar\u00edn-Borras, V. Mu\u00f1oz-Sanjos\u00e9, P. Rodr\u0131guez-Hernandez, A. Mu\u00f1oz, E. Perez-Gonzalez,\nF. J. Manjon and J. Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL\nREVIEW B       Volume:<\/strong>    85,Pag<\/strong>.<\/strong>:  195139<\/p>\n\n\n\n

Abstract:<\/strong> This paper reports an\nexperimental and theoretical investigation on the electronic structure of\nbismuth selenide (Bi2Se3) up to 9 GPa. The optical gap of Bi2Se3 increases from 0.17 eV at ambient pressure to 0.45 eV\nat 8 GPa. The quenching of\nthe Burstein-Moss effect in degenerate samples and the shift of the\nfree-carrier plasma frequency to lower energies reveal a quick decrease of the\nbulk three-dimensional (3D) electron concentration under pressure. On\nincreasing pressure the behavior of Hall electron concentration and mobility\ndepends on the sample thickness, consistently with a gradual transition from\nmainly 3D transport at ambient pressure to mainly two-dimensional (2D)\ntransport at high pressure. Two-carrier transport equations confirm the\ntrapping of high-mobility 3D electrons, an effect that can be related to a\nshallow-to-deep transformation of donor levels, associated with a change in the\nordering of the conduction band minima. The high apparent areal density and low\nelectron mobility of 2D electrons are not compatible with their expected\nproperties in a Dirac cone. Measured transport parameters at high pressure are\nmost probably affected by the presence of holes, either in an accumulation\nsurface layer or as minority carriers in the bulk.<\/p>\n\n\n\n

DOI<\/strong>: 10.1103\/PhysRevB.85.195139<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Unraveling the Coordination Geometry of Copper(II) Ions in Aqueous Solution through Absorption Intensity<\/summary>
\n

Author<\/strong>(s): <\/strong>Susana G\u00f3mez-Salces, Fernando Aguado, Rafael Valiente,\nand Fernando Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Angewandte Chemie                 Volume:<\/strong>  124   Pag.:  9469 \u20139472<\/p>\n\n\n\n

Abstract:<\/strong> Coordination\nChemistry<\/p>\n\n\n\n

DOI<\/strong>:  10.1002\/ange.201202033<\/p>\n\n\n\n

Keywords:<\/strong> coordination\nchemistry, copper Jahn\u2013 Teller distortion, structure\nelucidation<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Anomalous High-Pressure Jahn-Teller Behavior in CuWO4<\/sub><\/summary>
\n

Author<\/strong>(s): <\/strong>J. Ruiz-Fuertes, A. Segura, F. Rodr\u00edguez, D. Errandonea and M. N. Sanz-Ortiz<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW LETTERS           Volume:<\/strong>  108                 Pagina<\/strong>:<\/strong>\n166402<\/p>\n\n\n\n

Abstract:<\/strong> High-pressure optical-absorption\nmeasurements performed in CuWO4<\/sub> up to 20 GPa provide experimental evidence of the persistence\nof the Jahn-Teller (JT) distortion in the whole\npressure range both in the low-pressure triclinic and in the high-pressure\nmonoclinic phase. The electron-lattice couplings associated with the eg<\/sub> (E* e) and t2g<\/sub> (T * e) orbitals of Cu2+<\/sup> in CuWO4<\/sub> are\nobtained from correlations between the JT distortion of the CuO6 octahedron and\nthe associated structure of Cu2+<\/sup> d-electronic levels. This\ndistortion and its associated JT energy (EJT) decrease upon compression in both\nphases. However, both the distortion and associated EJT increase sharply at the\nphase-transition pressure (PPT \u00bc 9:9 GPa),\nand we estimate that the JT distortion persists for a wide pressure range not\nbeing suppressed up to 37 GPa. These results shed\nlight on the transition mechanism of multiferroic\nCuWO4<\/sub>, suggesting that the pressure-induced structural phase\ntransition is a way to minimize the distortive effects associated with the\ntoughness of the JT distortion.<\/p>\n\n\n\n

DOI <\/strong>10.1103\/PhysRevLett.108.166402<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Exciton dynamics in 1D (CH3<\/sub>)4<\/sub>NMnCl3<\/sub> by time-resolved spectroscopy: influence of the exchange interaction by pressure<\/summary>
\n

Author<\/strong>(s): <\/strong>Nataf Lucie,\nValiente Rafael, Gonz\u00e1lez Jes\u00fas and Rodriguez\nFernando<\/p>\n\n\n\n

Source:<\/strong> 6th Asian Conference on\nHigh Pressure Research, August 8 – 12, 2012, Beijing, China<\/p>\n\n\n\n

Abstract:<\/strong> The (CH3<\/sub>)4<\/sub>NMnCl3<\/sub>\ncrystal (TMMC) consists of linear chains of face-sharing MnCl6<\/sub> 4-<\/sup>\noctahedra, which has received considerable attention\nas an ideal one-dimensional (1D) system of exchangecoupled\nMn2+<\/sup> ions. The intrachain Mn-Mn interaction is several orders of magnitude bigger\nthan the interchain Mn-Mn\ninteraction [1], hence those properties related to the exchange-coupled Mn2+\n<\/sup>ions like 1D magnetism [1,2] or 1D excitation transfer (migration)\nyielding unusually intense photoluminescence (PL) [3,4] were widely\ninvestigated on this model material. In contrast to other 2D and 3D Mn2+<\/sup>\nsystems, the atomic arrangement in TMMC provides a 1D excitonic\nconfinement leading to substantial reduction of exciton\ncapture by non-PL traps. Besides the strong axial anisotropy at the Mn2+ site\nin TMMC is noteworthy. It is responsible for the large crystal-field strength\nat Mn2+<\/sup> (10Dq = 0.8 eV) yielding an\nintense PL band at 630 nm at ambient conditions [4,5]\nwith one of the largest pressure shifts: 23 nm\/GPa\n[6]. This makes TMMC attractive for using as pressure gauge, particularly, in\nlow pressure experiments (below tenths of GPa)\nrequiring fine tuning and precise pressure determination [6]. Here we present\nan exciton dynamics study in TMMC by time-resolved\nspectroscopy (emission and excitation), optical absorption and time-dependent\nPL measurements as a function of pressure in correlation with previous magnetic\nand structural data [1]. Interestingly, pressure provides an attractive way to\nmodulate the intrachain Mn-Mn\nexchange interaction making it easier the analysis of exciton\ndynamics (exciton transfer and capture) governing PL\nproperties. Instead of dealing with PL decay curve I(t)\nshape analysis, we focus on the intrachain energy\ntransfer processes from the averaged lifetime parameter, \u03c4av(P),\nas a function of pressure. The higher accuracy attained in measuring \u03c4av(P)\nwith respect to I(t) allows us a precise determination of the Mn-Mn transfer frequency and its dependence on the exchange\ninteraction (pressure). The obtained results rise the\nquestion on whether energy transfer takes place according to a random-walk\nmodel or whether there is a driving force reducing the exciton\ncapture time at non-PL impurities. The effects of exchange interaction in the exciton migration and PL efficiency will be analyzed.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure optical absorption studies of double-walled carbon nanotubes<\/summary>
\n

Author<\/strong>(s): <\/strong>Jes\u00fas Marquina, Enmanuel\nFlahaut, and Jes\u00fas Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong> P hys. Status Solidi\nRRL   (Rapid Research Letters) Volume:<\/strong>  1-3<\/p>\n\n\n\n

Abstract:<\/strong> In this Letter the\nelectronic properties of double-walled carbon nanotubes\n(DWCNTs) were studied by transmission measurements as a function of hydrostatic\npressure up to 10 GPa. The\nenergies of the optical transitions between the Van Hove singularities decrease\nwith increasing pressure, which can be attributed to pressure-induced\nhybridization and symmetry-breaking effects. We observed a linear behavior in\nthe pressure-induced shift of the optical transitions. This is in good\nagreement with previous studies on single-walled carbon nanotubes\n(SWCNTs). High-resolution TEM image of a bundle of DWCNTs (A), histogram of the\nnumber of walls (B), and diameter distribution for CNT samples plotted from 100\nHRTEM images (C). <\/p>\n\n\n\n

DOI <\/strong>10.1002\/pssr.201206280<\/p>\n\n\n\n

Keywords\n<\/strong>double-walled\ncarbon nanotubes, optical absorption, high-pressure\neffects, Van Hove singularities<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Lattice dynamic and optical properties of Zn1-x<\/sub>Cox<\/sub>O under high pressure: Wurtzite to Rock Salt phase transition <\/summary>
\n

Author<\/strong>(s): <\/strong>C. Renero-Lecuna,\nR. Mart\u00edn-Rodr\u00edguez, G. Almonacid, R. Valiente, A.\nSegura, V. Mu\u00f1oz, J. Gonz\u00e1lez, F. Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> 15th\nInternational Conference High Pressure Semiconductor Physics        Fecha<\/strong>\/Lugar :<\/strong> <\/em>Montpellier 25th-27th July ORAL (Francia)<\/em><\/p>\n\n\n\n

Abstract:<\/strong> During\nthe last 50 years a huge amount of research has been made about ZnO due to its optical and electronic properties as a wide\nband gap semiconductor. This material shows an ample variety of applications in\noptoelectronics, bioscience, and sensors or even in cosmetics. This research\nhas increased even more the last decade with the development of the nanoscience, paying more attention to ZnO\nnanostructures (nanoparticles, thin films, nanowires) doped with transition metals ions. <\/p>\n\n\n\n

We report an investigation on the optical properties of Co2+<\/sup>-doped\nZnO at high pressure by optical absorption and\nphotoluminescence. The absorption spectrum of wurtzite\nW-Zn1-x<\/sub>Cox<\/sub>O shows three main differences with respect to\npure W-ZnO: i<\/strong>) <\/strong>the\nfundamental band-to-band absorption edge is shifted to higher photon energies, ii)\n<\/strong>a charge-transfer-related broad band appears at energies just below (and\noverlapping) the band-to-band edge, and iii) <\/strong>well defined absorption\nbands related to d-d transitions of tetrahedral Co2+<\/sup> are observed.\nAll these features remained at pressures up to 8 GPa where the W to RS phase transition takes place.\nBeyond this pressure an abrupt change in the visible absorption band intensity\nfor the bulk is observed [1] whereas in nanoparticles,\nthe transition is observed at lower pressures ca. 5 GPa, and at 15 GPa for thin\nfilms. <\/p>\n\n\n\n

Photoluminescence was measured in all the conformations of W-Zn1-x<\/sub>Cox<\/sub>O\nup to the transition pressure. At room temperature (RT) a broad band emission\nis observed around 1.8 eV. This emission is related\nto the 4<\/sup>T1(P), 2<\/sup>E(G), 2<\/sup>T1(G)\nto ground state transition (4<\/sup>A2), as low temperature luminescence\nmeasurements revealed. This vibronic side band arises\ndue to the electron-phonon coupling associated to the 4<\/sup>T1(P).\n<\/p>\n\n\n\n

The W-to-RS phase transition is observed in the three optical\nabsorption features: i<\/strong>) <\/strong>the fundamental\nedge shifts to much higher photon energies, ii) <\/strong>the charge-transfer band\nvirtually disappears (or overlaps the direct transition of the RS phase), and iii)\n<\/strong>the d-d Co2+ absorption band around 2 eV\ndecreases its intensity by an order of magnitude and shifts to higher energies\n(2.5 eV) as a consequence of the modification from a\ntetrahedral to a octahedral coordination symmetry. We also show that Co2+ luminescence\ndrastically reduces and eventually disappears at the W-RS transition pressure. <\/p>\n\n\n\n

Also the high-pressure behaviour of the\noptical phonons in W-Zn1-xCoxO is studied by Raman spectroscopy. The pressure\ndependence of the zone-centre phonons (E2, A1, and E1) was measured for the W\nstructure up to the hexagonal-to-cubic phase transition near 8 GPa. Above this pressure some\nnon-active Raman modes were observed due to the distortion and the\npolycrystalline nature of the sample after two phase transitions. The phase\ntransition is fully reversible for the bulk material at ca. 3 GPa.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL PROPERTIES OF ZNO: CO2+<\/sup> UNDER HIGH PRESSURE<\/summary>
\n

Author<\/strong>(s): <\/strong>CARLOS RENERO-LECUNA<\/p>\n\n\n\n

Source:<\/strong> XI IKKS\n2012 (International Krutyn Summer School) –\n\u00abCutting Edge Luminescent Materials: Shifting the Frontiers\u00bb              Fecha<\/strong>\/Lugar :<\/strong> <\/em>Septiembre 23-29\n2012 ORAL <\/em><\/p>\n\n\n\n

Abstract:<\/strong> During\nthe last 50 years a huge amount of research has been made about ZnO due to its optical and electronic properties as a wide\nband gap semiconductor. This material shows an ample variety of applications in\nthe optoelectronic industry, bioscience, and sensors or even in cosmetics. This\nresearch has increased even more the last decade with the development of the nanoscience, paying more attention to ZnO\nnanostructures (nanoparticles, thin films, nanowires) doped with transition metals ions. <\/p>\n\n\n\n

We report an investigation on the optical properties of Co2+<\/sup>-doped\nZnO at high pressure by optical absorption, photo\nluminescence (PL) and Raman spectroscopy. The absorption spectrum of wurtzite W-Zn1-x<\/sub>Cox<\/sub>O shows three main\ndifferences with respect to pure ZnO: i) the fundamental band-to-band absorption edge is shifted\nto higher photon energies, ii) a broad band related to charge-transfer transition\nappears at energies just below (and overlapping) the band-to-band edge, and\niii) well defined absorption bands related to d-d transitions of tetrahedral Co2+<\/sup>\nare observed. All these features are observed at pressures as high as 15 GPa for thin films [1]. By\ncontrast, in nanoparticles, the transition to the\nrock-salt (RS) phase is observed at lower pressures ca. 5 GPa, and in bulk is observed around 9 GPa and with an abrupt change in the visible absorption\nband intensity [2]. PL was measured in all the conformations of W-Zn1-x<\/sub>Cox<\/sub>O\nup to the transition pressure. At room temperature (RT) a broad band emission\nis observed. This emission is related to the 4T1<\/sub>(P)\nto ground state transition (4A2<\/sub>) and a vibronic\nside band as low temperature and ambient pressure PL measurements revealed.\nThis vibronic side band is due to the electron-phonon\ncoupling associated to the 4T1<\/sub>(P). The\nW-to-RS phase transition is observed in the three optical absorption features: i) the fundamental edge shifts to much higher photon\nenergies, ii) the charge-transfer band virtually disappears (or overlaps the\ndirect transition of the RS phase), and iii) the d-d Co2+<\/sup> absorption\nband around 2 eV decreases its intensity by an order\nof magnitude and shifts to higher energies (2.5 eV)\nas a consequence of the modification from a tetrahedral to a octahedral\ncoordination symmetry. The phase transition also changes the emission spectra\nof the W-Zn1-x<\/sub>Cox<\/sub>O. Upwards the transition pressure, the\nPL disappears abruptly and no peak is measured. Also the high-pressure behaviour of the optical phonons in W-Zn1-x<\/sub>Cox<\/sub>O\nis studied by Raman spectroscopy. The pressure dependence of the zone-centre\nphonons (E2, A1, and E1) was measured for the W structure up to the\nhexagonal-to-cubic phase transition near 8 GPa. Above this pressure some non-active Raman modes\nwere observed. In the pressure downstroke the bulk W-Zn1-x<\/sub>Cox<\/sub>O\ntransited from the RS to the W phase at ca. 3 GPa. This behaviour is in\ncontrast to the one observed in W-Zn1-x<\/sub>Cox<\/sub>O thin films or\nnanoparticles, since thin films with Co2+<\/sup> and\nall nanocrystalline Zn1-xCoxO samples behaves in a\ndifferent way than the bulk, some of them even remains in the RS phase at\nambient pressure after the phase transition. Comparison between Co2+<\/sup>\nluminescence in its 3 different conformations is measured at ambient pressure.\nPL at room temperature is observed for the first time in NPs.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced rutile-to-fluorite-type transition in CoF2<\/sub> studied by x-ray absorption, Raman spectrosocpy and electronic absorption<\/summary>
\n

Author<\/strong>(s):<\/strong> M. N. Sanz-OrtizA, L. Nataf, J. A. Barreda Arg\u00fceso, F.\nRodr\u00edguez, F. Aguado, R.ValienteC, J. Gonz\u00e1lez, F. Baudelet<\/p>\n\n\n\n

Abstract:<\/strong> MX2<\/sub>\nbinary compounds (M: cation; X: O, F, Cl) show an ample variety of crystal structures related to\nchanges of the cation coordination number. Type\nstructures like \u03b1-quartz (SiO2<\/sub>), rutile\n(TiO2<\/sub>, MgF2<\/sub>, MnF2<\/sub>, CoF2<\/sub>),\nfluorite (CaF2<\/sub>, SrCl2<\/sub>), cotunnite\n(PbCl2<\/sub>) at ambient conditions are examples of such a behaviour. For a given compound, crystal compression\ninduces structural changes yielding increase of coordination number [1]. So\napplication of high external pressure allows us to move along the phase diagram\ntowards more compact structures as it is illustrated in the figure for some\nalkaline-earth and transition-metal fluorides. In the latter compound family,\nsuch phase transformation may involve significant modifications in the material\nproperties as a consequence of the concomitant changes of the 3d-related electronic structure\nassociated with the change of cation coordination\n(crystal-field strength) and magnetic interactions (M-M distances and superexchange pathways) [2]. This work reports an x-ray\nabsorption study on the local structure variation around Co2+<\/sup> (EK = 7.723 keV)\nin CoF2 as a function of pressure in the 0 \u2013 300 kbar.\nIt is worth noting the high pressure critical value for the rutile-fluorite\nphase transition, Pc =150 kbar, in comparison to isomorphous transition-metal fluorides. EXAFS and XANES\nanalysis will be discussed.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Synthesis and optical properties of Zn1-x<\/sub>Cox<\/sub>O as nanoparticles, thin film and single crystal<\/summary>
\n

Author<\/strong>(s): <\/strong>C. Renero-Lecuna, R. Mart\u00edn-Rodr\u00edguez, G.\nAlmonacid, A. Segura, R. Valiente, J. Gonz\u00e1lez, F.\nRodr\u00edguez<\/p>\n\n\n\n

Source<\/strong>: <\/strong>NanoSpain 2012                                    Fecha\/Lugar :<\/strong> <\/em>Santander 27 feb. 1 marzo (SPAIN)<\/em><\/p>\n\n\n\n

Abstract:<\/strong> Since the last 50\nyears a huge amount of research has been made about ZnO\ndue to its optical and electronic properties as a wide band gap semiconductor.\nThis research has increased even more the last decade with the development of\nthe nanoscience, paying more attention to ZnO nanostructures (nanoparticles,\nthin films, nano wires)\ndoped with transition metals ions such as Co2+<\/sup> or Mn2+<\/sup>.\nThese materials show a wide variety of applications in the optoelectronic\nindustry, bioscience, sensors or even in cosmetics. <\/p>\n\n\n\n

In\nthis work, thin films (TF) were grown following the pulsed laser deposition\n(PLD) method over a sapphire substrate. A SEM image shows several round shape Zn1-x<\/sub>Cox<\/sub>O of ca. 15 nm and\nthickness about 100 nm. Colloidal nanoparticles of wurtzite (W) Zn1-x<\/sub>Cox<\/sub>O were prepared\nusing hydrolysis and condensation of acetates solution in dimethyl\nsulfoxide [1]. Some TEM images show spherical nanoparticles with an average diameter of ca. 4 nm. ZnOCo single crystals with different Co2+<\/sup> concentrations\nhave been obtained by physical vapour transport (PVT)\nfor comparing their optical and magnetic properties with those observed in\nnanostructures. <\/p>\n\n\n\n

We\nreport an investigation of their optical properties under high pressure and low\ntemperature by means of optical absorption and photoluminescence. In Zn1-x<\/sub>Cox<\/sub>O\nthin films [2], absorption spectrum of W-Zn1-x<\/sub>Cox<\/sub>O shows\nthree main differences with respect to pure W-ZnO: i) the fundamental band-to-band absorption edge is shifted\nto higher photon energies, ii) a broad band related to charge-transfer\ntransition appears at energies just below (and overlapping) the band-to-band\nedge, and iii) well defined absorption bands related to d-d transitions of\ntetrahedral Co2+<\/sup> are observed. All these features are observed at\npressures as high as 15 GPa\nfor most concentrations. By contrast, in nanoparticles,\nthe transition to the rock-salt (RS) phase is observed at progressively lower\npressures as the Co2+<\/sup> concentration increases [2], and in bulk is\nobserved around 9 GPa and\nwith an abrupt change in the visible absorption band intensity. <\/p>\n\n\n\n

The\ntransition to the RS phase is observed in the three absorption features: i) the fundamental edge shifts to much higher photon\nenergies, ii) the charge-transfer band virtually disappears (or overlaps the\ndirect transition of the RS phase), and iii) the d-d Co2+<\/sup> absorption\nband around 2 eV decreases its intensity by a factor\n10 and shifts to higher energies (2.5 eV) as a\nconsequence of the modification from a tetrahedral to a octahedral coordination\nsymmetry. <\/p>\n\n\n\n

A comparison between low temperature Co2+<\/sup> photoluminescence\nat around 1.8 eV, which is assigned to the 4<\/sup>T2<\/sub>\n\u00e04<\/sup>A2<\/sub>\ntransition.<\/strong> <\/strong><\/p>\n\n\n\n

The\nhigh-pressure behaviour of optical phonons in W-ZnCoO is studied by Raman spectroscopy at room temperature.\nThe pressure dependence of the zone-centre phonons (E2<\/sub>, A1<\/sub>,\nand E1<\/sub>) was measured for the W\nstructure up to the hexagonal-to-cubic phase transition near 14 GPa. Above this pressure no active\nmode was observed. In the pressure down-stroke and independently of the Co2+<\/sup> concentration, all studied nanoparticles remain in the RS phase at ambient pressure.\nThis behaviour is also in contrast to the one\nobserved in ZnCoO thin films, in which only films\nwith Co2+<\/sup> concentrations larger\nthan 25% remain in the RS phase at ambient pressure.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

What could a XtremeC beamline unveil in materials science?<\/summary>
\n

Author(s): <\/strong>Fernando\nRodriguez<\/p>\n\n\n\n

Source:<\/strong> Advanced\nSeminar on \u00abPerspectives for Neutron Science in Novel & Extreme\nconditions\u00bb <\/em>          Fecha<\/strong>\/Lugar :<\/strong> 27<\/em>th <\/em>\u2013 31<\/em>st <\/em>May 2012, Zaragoza (Spain)<\/em><\/p>\n\n\n\n

Abstract:<\/strong> It is commonly\naccepted that experimental research under Extreme Conditions is mainly led by\nscientists having access to large facilities of synchrotron and neutron\nsources. The reason is probably due to the especially dedicated beamlines operating with beams (flux and energy range) and\nexperimental setups that make them unique to explore the structure of condensed\nmatter systems under the hard requirements imposed by sample environments under\nextreme conditions. Although beamstations incorporate\nthe newest developments in high pressure, low\/high temperature or high magnetic\nfield, there are important novel phenomena in hard and soft condensed matter\nwhich are yet difficult to investigate with present experimental facilities due\nto limitations of sample volume, pressure cells or especial environments. Hence\nfuture developments in Extreme Conditions science must consider go beyond\npresent instrumental limitations and at the same time offer an adequate\ninfrastructure for users to do reliable and efficient experiments at large facilities.\nFurthermore, the possibility of conducting experiments at large facilities\nusing either x-ray or neutron beams jointly with standard spectroscopic techniques\n(Raman, optical absorption, photoluminescence, etc.) is noteworthy as it\nprovides a systematic in situ <\/em>sample characterization in order to\nreproduce given experimental conditions. Furthermore this procedure gives a\ndirect link between experimental results obtained at home laboratories or\nsynchrotron facilities, with high-pressure experiments conducted in neutron\nfacilities. In this way, developments in high volume, high pressure, and high magnetic\nfield can be crucial to unravel a large variety of physical phenomena related\nto the interplay between spin state, electron-phonon coupling and orbital order\ngoverning the optical, magnetic and electrical properties, and that can be\nmodified applying external pressure. <\/p>\n\n\n\n

Spin\ntransition phenomena occurring in pure or diluted transition-metal oxides like magnetite\nFe2O3 [1], magnesiow\u00fcstite (Fe,Mg)O\n[2], multiferroic BiFeO3 [3,4], delafossite\n(CuFeO2) [5], low-spin cobaltite (La,Sr)CoO3 [6] or\nhigh-spin CoF3 or CsMnF4 drive structural changes with pressure affecting their\nmagnetic and electrical properties: highspin (intermediate\nspin) to low-spin transitions; charge-transfer processes; insulating-metal transitions,\netc. These systems illustrate how investigations using neutron probes under high\npressure (30-40 GPa) and\nhigh magnetic field (20 T) can be crucial to reveal and eventually understand\nstructural modifications and related phenomena yet unsolved in materials\nscience. This is a contribution from the High Pressure & Spectroscopy\nGroup, University of Cantabria.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

2011<\/strong><\/p>\n\n\n\n

Anharmonic properties of raman modes in double wall carbon nanotubes<\/summary>
\n

Author(s):<\/strong> J. Marquina, CH. Power, J.M.\nBroto, E. Flahaut, and J.\nGonzalez<\/em><\/p>\n\n\n\n

Source<\/strong>:<\/strong> Revista Mexicana de F\u00edsica             Volume<\/strong>:<\/strong> 57(1)     Issue<\/strong>:<\/strong>                    Pag<\/strong>:<\/strong> 510-517<\/p>\n\n\n\n

Abstract:<\/strong> The temperature dependence of the radial breathing modes (RBMs) and the zone-center tangential optical phonons (G-bands) of doublewalled carbon nanotubes (DWCNTs) has been investigated between 300 and 700 K using Raman scattering. As expected, with increasing temperature, the frequencies of the Raman peaks, including the RBMs and G-bands downshift simultaneously. We show here that the temperature dependence of the RBMs can be fitted by a simple linear dependence and different RBMs have different frequency shifts. We observe a noticeable nonlinearity in the temperature dependence of the G-band associated with the outer semiconducting tube G+ext (s). The deviation from the linear trend is due to the contribution of the third-order anharmonic term in the lattice potential energy with a pure temperature effect. An estimated value of 1.5 for the Gr\u00fcneisen parameter of the G+ext (s) band was found.<\/p>\n\n\n\n

DOI:<\/strong> <\/p>\n\n\n\n

Keywords: <\/strong>Raman spectroscopy; double wall carbon nanotubes; high-temperature; anharmonicity; Gr\u00fcneisen parameter<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Dependencia con la presi\u00f3n del \u00edndice de refracci\u00f3n del AgGaS2<\/summary>
\n

Author<\/strong>(s):<\/strong> Ch.\nPower, E. Calder\u00f3n, J. Gonz\u00e1lez y J.C. Chervin<\/p>\n\n\n\n

Source<\/strong>:<\/strong> Revista Mexicana de F\u00edsica             Volume<\/strong>:<\/strong> 57(1)     Issue<\/strong>:<\/strong>                    Pag<\/strong>:<\/strong> 35-39<\/p>\n\n\n\n

Abstract:<\/strong> In this work, we study the pressure behavior of the\noptical absorption spectrum of a single crystal AgGaS2<\/sub>, taking\nmeasurements in the infrared energy range from 0.30 up to 0.70 eV for pressures values P below 4GPa and room temperature\nT, using a diamond anvil cell in combination with infrared micro spectroscopy\ntechnique [1]. With this study, we determine the refraction index n <\/em>variations\nin terms of pressure within the stability range of the chalcopyrite structure\n[2-6] as well as the changes under pressure of both the static (\u03b50<\/sub>) and high frequency\n(\u03b500<\/sub>) dielectric constants. These results can be compared\nwith the experimental values reported by Boyd et al. <\/em>[7] <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.81.075120 <\/p>\n\n\n\n

Keywords: <\/strong>I-III-VI2 semiconductor;\ninfrared; high pressure.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Espectroscopia Brillouin de lubricantes (PDV-Supra Premium SJ, de PDV) bajo altas presiones<\/summary>
\n

Author(s):<\/strong> Chrystian Power, Jes\u00fas Gonz\u00e1lez,\nEdgar Belandria, Jean Claude Chervin\ny Alain Polian<\/p>\n\n\n\n

Source \n<\/strong>Scientific Journal from the Experimental\nFaculty of Sciences  Volume:<\/strong> 19 N\u00ba1  Pag<\/strong>: 41-49<\/p>\n\n\n\n

Abstract:<\/strong> We conducted the study of the variation\nin pressure through the diamond anvil cell (DAC) up to 16GPa, of the acoustic vibrational modes in multigrade\nmotor oil SAE 15W SUPRA SJ 40, which is a commercial lubricant of high\nantioxidant protection, produced in Venezuela with certificate API-SJ, for\ngasoline engines LPG or CNG. From Brillouin\nbackscattering spectroscopy we have determined the transverse sound speed,\ncorresponding to different phase transitions and within their domains of\nstability. In the pressure range close to 1GPa we observe the liquid phase\nfollowed by the phase transition to the glass state, the no-discontinuity in\nthe Brillouin shift indicates that the phase\ntransition liquid-glass is a phase transition of second order, for pressures up\nto 4GPa we observe two phase transitions of first order, which we consider amorphous\nsolid phases. <\/p>\n\n\n\n

Key words: <\/strong>diamond anvil cell, Brillouin,\nsound speed, phase transitions.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure optical absorption studies of double-walled carbon nanotubes<\/summary>
\n

Author(s):<\/strong> Jes\u00fas Marquina, Enmanuel Flahaut, and Jes\u00fas Gonz\u00e1lez<\/p>\n\n\n\n

Source:<\/strong> P hys. Status Solidi\nRRL   Volume:<\/strong> 1-3<\/p>\n\n\n\n

Abstract:<\/strong> T In this Letter the electronic properties\nof double-walled carbon nanotubes (DWCNTs) were\nstudied by transmission measurements as a function of hydrostatic pressure up\nto 10 GPa. The energies of\nthe optical transitions between the Van Hove singularities decrease with\nincreasing pressure, which can be attributed to pressure-induced hybridization\nand symmetry-breaking effects. We bserved  a linear behavior in\nthe pressure-induced shift of the optical transitions. This is in good\nagreement with previous studies on single-walled carbon nanotubes\n(SWCNTs). High-resolution TEM image of a bundle of DWCNTs, histogram of the\nnumber of walls, and diameter distribution for CNT samples plotted from 100\nHRTEM images.<\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/pssr.201206280<\/p>\n\n\n\n

Keywords: <\/strong>double-walled carbon nanotubes,\noptical absorption, high-pressure effects, Van Hove singularities<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure Raman spectroscopy and lattice-dynamics calculations on scintillating MgWO4<\/sub>: Comparison with isomorphic compounds<\/summary>
\n

Author(s):<\/strong> J. Ruiz-Fuertes,  D. Errandonea, S. Lopez-Moreno, J. Gonzalez, O. Gomis, R. Vilaplana, F. J. Manjon, A. Mu\u00f1oz, P. Rodr\u0131guez-Hernandez, A. Friedrich, I. A. Tupitsyna, and L. L. Nagornaya<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B       Volume:<\/strong> 83          Pag<\/strong>: 214112<\/p>\n\n\n\n

Abstract:<\/strong> Raman scattering measurements and\nlattice-dynamics calculations were performed on magnesium tungstate\n(MgWO4) under high pressure up to 41 GPa. Experiments were carried out on a selection of\npressure media. The influence of nonhydrostaticity on\nthe structural properties of MgWO4\nand isomorphic compounds is\nexamined. Under quasihydrostatic conditions, a phase\ntransition was found at 26 GPa\nin MgWO4. The high-pressure phase is tentatively assigned to a triclinic\nstructure similar to that of CuWO4. We also report and discuss the Raman symmetries,\nfrequencies, and pressure coefficients in the low- and high-pressure phases. In\naddition, the Raman frequencies for different wolframites\nare compared and the variation of the mode frequency with the reduced mass\nacross the family is investigated. Finally, the accuracy of theoretical\ncalculations is systematically discussed for MgWO4, MnWO4, FeWO4, CoWO4, NiWO4, ZnWO4, and CdWO4.<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.83.214112<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-pressure vibrational and optical study of Bi2<\/sub>Te3<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> R. Vilaplana, O. Gomis, F. J. Manjon, A. Segura, E. Perez-Gonzalez, P. Rodr\u0131guez-Hernandez, A. Mu\u00f1oz, J. Gonzalez, V. Mar\u0131n-Borras, V. Mu\u00f1oz-Sanjose, C. Drasar\n and V. Kucek<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B       Volume:<\/strong> 84          Pag<\/strong>: 104112<\/p>\n\n\n\n

Abstract:<\/strong> We report an experimental and\ntheoretical lattice dynamics study of bismuth telluride (Bi2Te3) up to 23 GPa together with an experimental\nand theoretical study of the optical absorption and reflection up to 10 GPa. The indirect bandgap of the\nlow-pressure rhombohedral (R-<\/em>3m<\/em>) phase (\u03b1<\/em>-Bi2Te3) was observed to decrease with pressure at a\nrate of \u22126meV\/<\/em>GPa. In regard to lattice dynamics, Raman-active modes of\n\u03b1<\/em>-Bi2Te3 were\nobserved up to 7.4 GPa. The\npressure dependence of their frequency and width provides evidence of the\npresence of an electronic-topological transition around 4.0 GPa. Above 7.4 GPa\na phase transition is detected to the C<\/em>2\/<\/em>m <\/em>structure.\nOn further increasing pressure two additional phase transitions, attributed to\nthe C2<\/em>\/<\/em>c <\/em>and\ndisordered bcc (Im-<\/em>3m<\/em>) phases, have been observed near 15.5 and 21.6 GPa in good agreement with the structures recently observedbymeans of x-raydiffractionat\nhighpressures inBi2Te3.After release of pressure the\nsample reverts back to the original rhombohedral\nphase after considerable hysteresis. Raman- and IR-mode symmetries,\nfrequencies, and pressure coefficients in the different phases are reported and\ndiscussed<\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.84.104112<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Organic_Inorganic Hybrids Assembled from Lanthanide and 1,4-Phenylenebis(phosphonate)<\/summary>
\n

Author<\/strong>(s): <\/strong>Zakariae Amghouz, Santiago\nGarc\u00eda-Granda, Jos\u00e9 R. Garc\u00eda,\nAbraham Clearfield and Rafael Valiente<\/p>\n\n\n\n

Source:<\/strong> American Chemical\nSociety                  Volume:<\/strong>  11   Pag.:  5289\u20135297<\/p>\n\n\n\n

Abstract:<\/strong> A series\nof novel organic_inorganic hybrids based on trivalent\nlanthanide (Ln = La, Ce,\nPr, Nd, Sm, Eu, Gd, Tb, Dy,\nHo) and 1,4-phenylbis(phosphonate)\nformulated as Ln[O3<\/sub>P(C6<\/sub>H4<\/sub>)PO3<\/sub>H]\nhas been obtained as single phases under hydrothermal conditions. In the\npraseodymium compound (Za1), single crystals have been obtained and the crystal\nstructure has been determined. Za1 crystallizes in the monoclinic space group, C2\/c,\nwith a = 5.6060(4) \u00c5, b = 20.251(7) \u00c5, c = 8.2740(6) \u00c5, \u03b2 = 108.52(1)_. All other compounds are isostructural\nto Za1 as confirmed by Rietveld refinement using\nX-ray powder diffraction data. Compounds are characterized by thermal analyses\n(TG-MS and SDTA), elemental analysis, IR spectra, and X-ray thermodiffraction\nanalysis. Their visible photoluminescence properties are also discussed.<\/p>\n\n\n\n

DOI<\/strong>:  dx.doi.org\/10.1021\/cg2008254<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Origin of the High Upconversion Green Luminescence Efficiency in \u03b2-NaYF4<\/sub>:2%Er3+<\/sup>,20%Yb3+<\/sup><\/summary>
\n

Author<\/strong>(s):<\/strong> C. Renero-Lecuna,\nR. Mart\u00edn-Rodr\u00edguez, R. Valiente, J. Gonz\u00e1lez, F. Rodr\u00edguez, K. W. Kramer and H. U. Gudel<\/p>\n\n\n\n

Source:<\/strong> Chemistry of Materials          Volume:<\/strong> 23          Pag<\/strong>: 3442\u20133448<\/p>\n\n\n\n

Abstract:<\/strong> Site-selective spectroscopy in\nhexagonal \u03b2-NaYF4:Er3+,Yb3+has revealed different environments for Er3+ ions\n(multisite formation). The low-temperature 4S3\/2f4I15\/2 Er3+green\nemission depends on the excitation wavelength associated with the 4F7\/2 Er3+ level.\nWe have studied the effect of hydrostatic pressure on the green, red, and\nblue Er3+ emission upon NIR excitation at \u223c980 nm, in order to establish the role played by energy resonance\nconditions and the multiple Er3+ sites due to the disordered structure for the upconversion (UC) process (energy tuning). The variation of\nphotoluminescence spectra and lifetimes as a function of pressure and temperature\nreveals that the origin of the high green UC efficiency of the \u03b2-NaYF4:Er3+,Yb3+ compound\nis mainly due to the multisite distribution, and the low phonon energy of the\nhost lattice. <\/p>\n\n\n\n

DOI:<\/strong> dx.doi.org\/10.1021\/cm2004227<\/p>\n\n\n\n

KEYWORDS:<\/strong> upconversion, NaYF4: Er3+, Yb3+, high pressure, luminescence, multisites,\nsite selective spectroscopy<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Raman characterization of carbon materials under non-hydrostatic conditions<\/summary>
\n

Author<\/strong>(s): <\/strong>E. del Corro, M. Taravillo, J. Gonzalez, V.G. Baonza<\/p>\n\n\n\n

Source: <\/strong>CARBON Elsavier Volume:<\/strong>\n49   Pag<\/strong>.<\/strong>:  973-979<\/p>\n\n\n\n

Abstract:<\/strong> Raman\nspectroscopy experiments on double-wall carbon nanotube\nand highly oriented pyrolytic graphite (HOPG) samples\nsubjected to non-hydrostatic conditions have been conducted in anvil cells to\nstudy the effect of the pressure\/stress on the bands assigned to defects.\nTypical diamond anvils used in high pressure experiments have been substituted by\nmoissanite (6H-SiC) and sapphire (Al2O3) anvils to\nallow the observation of the D band (around 1350 cm_1) and the second-order\nRaman scattering without interference. We demonstrate that Raman experiments at\nhigh pressure provide unique information to probe the mechanical behaviour of carbon materials (CMs).We also show that this\ncan be also a powerful technique to assign controversial spectral features such\nas those appearing in the second order region of the spectra of CMs. In HOPG\nsamples we find that the D0\/D band intensity ratio is independent of stress.\nThe results indicate that an increase of non-hydrostatic stresses on HOPG\ngenerates graphitic domains with sizes around 20\u201330 nm when the sample is\nrecovered to room conditions. <\/p>\n\n\n\n

DOI<\/strong>:10.1016\/j.carbon.2010.09.064<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopic study of Cu2+<\/sup>\/Cu+<\/sup> doubly doped and highly transmitting glasses for solar spectral transformation<\/summary>
\n

Author<\/strong>(s): <\/strong>Susana G\u00f3mez, I\u00f1igo Urra ,\nRafael Valiente , Fernando Rodr\u00edguez<\/p>\n\n\n\n

Source:<\/strong> Elsevier\nB.V. Solar\nEnergy Materials & Solar Cells                    Volume:<\/strong>  95   Pag.:  2018\u20132022<\/p>\n\n\n\n

Abstract:<\/strong> This work\ninvestigates the formation of photoluminescence (PL) centres\nin high-transmission glasses (HTG) doped with Cu2O and their capability to\ntransform the solar spectrum by absorption\/emission via upconversion,\ndownconversion and Stokes-shifted PL into a more\nefficient spectrum for photovoltaic applications. Both the\ngreen PL Cu+ and the non-PL Cu2+ centres are formed\nin HTG, although their relative concentration depends on the thermal treatment\nand the presence of other codopants. Given that the\nabsorption spectrum of Cu+ lies around the HTG band gap, measurement of the\nabsorption coefficient a(l) for these absorption bands is not easy due to\ncorrections between the reflection coefficient and chromatic dispersion. We\npresent a procedure, named two-thickness method, to extract the actual\nabsorption coefficient for the spectrum of each formed centre. In addition it\nprovides the relative Cu+\/Cu2+ concentration as well as their absolute values.\nAnalysis of the spectra also provides information on the absorption cross\nsection, transition energy and bandwidth of each band, the knowledge of which\nis essential to check the suitability of such centres\nfor photovoltaic applications in silicon solar cells<\/p>\n\n\n\n

DOI<\/strong>:  10.1016\/j.solmat.2010.07.022<\/p>\n\n\n\n

Keywords<\/strong>: Glasses,\nCu+, Cu2+, Solar converter, Luminescence<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Temperature and pressure dependence of the optical properties of Cr3+<\/sup>-doped Gd3<\/sub>Ga5<\/sub>O12<\/sub> nanoparticles<\/summary>
\n

Author(s): <\/strong>R Mart\u00edn-Rodr\u00edguez,\nR Valiente, F Rodr\u00edguez and\nM Bettinelli<\/p>\n\n\n\n

Source:<\/strong> IOP PUBLISHING NANOTECHNOLOGY                        Volume:<\/strong>  22   Pag.:  265707                                 Online\nat stacks.iop.org\/Nano\/22\/265707<\/p>\n\n\n\n

Abstract:<\/strong> Since the\ncrystal-field strength at the Cr3+<\/sup> site is very close to the\nexcited-state crossover (ESCO), this work investigates the optical properties\nof Cr3+<\/sup>-doped Gd3<\/sub>Ga5<\/sub>O12<\/sub> (GGG) nanoparticles as a function of temperature and pressure in\norder to establish the effect of the ESCO on the optical behaviour\nof nanocrystalline GGG. Luminescence, time-resolved\nemission and lifetime measurements have been performed on GGG:0.<\/em>5%\nCr3+<\/sup> nanoparticles in the 25\u2013300 K\ntemperature range, as well as under hydrostatic pressure up to 20 GPa. We show how low temperature and high pressure\nprogressively transforms Cr3+<\/sup> 4<\/sup>T2 <\/sub>\u21924<\/sup>A2<\/sub>\nbroadband emission into a ruby-like 2<\/sup>E \u21924<\/sup>A2<\/sub>\nluminescence. This behaviour together with the\nlifetime dependence on pressure and temperature are explained on the basis of\nthe spin\u2013orbit interaction between the 4<\/sup>T2<\/sub> and 2<\/sup>E\nstates of Cr3+<\/sup>.<\/p>\n\n\n\n

DOI<\/strong>:  10.1088\/0957-4484\/22\/26\/265707<\/p>\n<\/div><\/details><\/div>\n\n\n\n

The effect of pressure on the crystal structure of bianthrone<\/summary>
\n

Author(s):<\/strong> Russell D. L. Johnstone, David Allan, Alistair Lennie,\nElna Pidcock, Rafael Valiente, Fernando Rodriguez, Jesus Gonzalez, John Warren\nand Simon Parsons<\/p>\n\n\n\n

Source \n<\/strong>Acta Crystallographica Section B   Volume:<\/strong> B67        226\u2013237<\/p>\n\n\n\n

Abstract:<\/strong> Bianthrone\n[10(10-oxoanthracen-9-ylidene)anthracen-9-one] consists\nof two tricyclic anthraceneone\nunits connected by a carbon\u2013carbon double bond. Crystals of the form obtained under\nambient conditions are yellow and contain folded centrosymmetric\nconformers in which the central ring of the anthraceneone\nunit is non-planar. When hydrostatic pressure is applied the crystals assume a\nred colouration which gradually deepens as pressures\nincreases. The colour change is limited in extent to\nthe surface of the crystals, the bulk remaining yellow. Comparison of\nhigh-pressure, single-crystal UV\u2013vis spectra and\npowder diffraction data demonstrate that the colour\nchange is associated with the formation of a polymorph containing a conformer\nin which the tricyclic fragments are planar and the\nmolecule is twisted about the central C\u2014C bond. Single-crystal diffraction data\ncollected as a function of pressure up to 6.5 GPa\nreveal the effect of compression on the yellow form, which consists of layers of\nmolecules which stack along the [010] direction. The structure remains in a\ncompressed form of the ambient-pressure phase when subjected to hydrostatic\npressure up to 6.5 GPa, and\nthe most prominent effect of pressure is to push the layers closer together.\nPIXEL calculations show that considerable strain builds up in the crystal as\npressure is increased with a number of intermolecular contacts being pushed\ninto destabilizing regions of their potentials<\/p>\n\n\n\n

DOI:<\/strong>:10.1107\/S0108768111009657<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical and magnetic characterisation of Co3<\/sub>C and Ni3<\/sub>C in LaAlO3<\/sub>: interplay between the spin state and Jahn\u2013Teller Effect<\/summary>
\n

Author<\/strong>(s):<\/strong> Marta N Sanz-Ortiz, Fernando Rodr\u00edguez, Jes\u00fas Rodr\u00edguez and Gerard Demazeau<\/p>\n\n\n\n

Source:<\/strong> IOP\nPUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER       Volume:23<\/strong>           Issue:<\/strong>                    Pag<\/strong>:<\/strong> 415501<\/p>\n\n\n\n

Online at\nstacks.iop.org\/JPhysCM\/23\/415501<\/p>\n\n\n\n

Abstract:<\/strong> The\ncoordination, the electronic structures and the spin of\nthe ground state of Ni3<\/sub>C (3d7<\/sub>) and Co3<\/sub>C (3d6<\/sub>)\nintroduced as impurities in LaAlO3<\/sub> are investigated through optical\nspectroscopy and magnetic measurements. The unusual trivalent valence state in\nboth transition-metal ions was stabilised via a\nsol\u2013gel process followed by high oxygen pressure treatments. We show that the\ncrystal-field strength at the nearly Oh transition-metal site in LaAlO3<\/sub>\nlocates Ni3<\/sub>C and Co3<\/sub>C near the spin state crossover,\nyielding a low-spin ground state in both cases. We analyse\nhow the interplay between the Jahn\u2013Teller (JT) effect\nand the spin state affects the magnetic moment of the ion and its temperature\ndependence. The optical spectra reveal a JT effect associated with a low-spin\nground state in Ni3<\/sub>C and with a thermally populated high-spin\nlow-lying first excited state in Co3<\/sub>C. The corresponding JT\ndistortions are derived from structural correlations. We conclude that the JT\neffect is unable to stabilise the intermediate spin\nstate in Co3<\/sub>C. A low-spin ground state in thermal equilibrium with a\nhigh-spin low-lying first excited state is detected in diluted Co3<\/sub>C-doped\nLaAlO3<\/sub>. These results are compared with those obtained in the parent\npure compounds LaNiO3<\/sub> and LaCoO3.<\/sub><\/p>\n\n\n\n

Keywords: <\/strong>Localization effects 72.15.Rn, Hopping transport 72.20.Ee, Weak localization 73.20.Fz, Spin-density waves<\/p>\n\n\n\n

Doi:<\/strong>10.1088\/0953-8984\/23\/41\/415501<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Weak Localization and electron-electron interaction in the layered compound CuFeTe2<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> A.Rivas-Mendoza. F. Gonzalez-Jim\u00e9nez,\nJ.M. Broto, H.Rakotob and J. Gonz\u00e1lez<\/p>\n\n\n\n

Source<\/strong>:<\/strong> REVISTA CUBANA DE F\u00cdSICA  (Agosto 2011)<\/p>\n\n\n\n

                Volume:28<\/strong>           Issue<\/strong>:<\/strong>                    Pag<\/strong>:<\/strong> No1<\/p>\n\n\n\n

Abstract<\/strong>:<\/strong> El estudio de las propiedades el\u00e9ctricas del compuesto\nlaminar CuFeTe2<\/sub> indica que hay tres reg\u00edmenes de conducci\u00f3n bien\ndiferenciados dependientes de la temperatura. Por debajo de TSDW ~ 300 K se ha\nreportado la formaci\u00f3n de un estado de Ondas de Densidad de Esp\u00edn (SDW), en el\nmarco de una transici\u00f3n metal no metal. Por debajo de 100 K (~ TSDW\/3) el\ncomportamiento de la resistencia el\u00e9ctrica como una funci\u00f3n de la temperatura y\nel campo magn\u00e9tico se atribuye a los electrones no condensados (cuasi\npart\u00edculas) en el estado SDW. A bajas temperaturas (1.8 – 20K), baja corriente (<\n1 mA) y campo magn\u00e9tico (0 <H <6 Tesla), los\nefectos de localizaci\u00f3n d\u00e9bil e interacciones electr\u00f3nicas aparecen. A\ntemperaturas intermedias (20 < T < 100 K) se observa un comportamiento de\nconductividad hopping. The study of the\nelectrical properties of the layered compound CuFeTe2<\/sub> shows that\nthere are three well differentiated conduction regimes depending on the\ntemperature. Below TSDW ~ 300 K the formation of a Spin Density Wave (SDW)\nstate has been reported, in the frame of a metal to non metal transition. Below\n100  K (~\nTSDW\/3) the behavior of the electrical resistance as a function of temperature\nand magnetic .eld is attributable to the still\npresent not condensed electrons (quasi particles) in the SDW state. At low\ntemperatures (1.8 – 20K), low current (< 1 mA) and\nmagnetic .eld (0<H <6 Tesla), the effects of\nweak localization and electronic interactions in two dimensions appear. At\nintermediate temperatures (20 < T < 100 K) a hopping conductivity\nbehavior is observed. <\/p>\n\n\n\n

Keywords: <\/strong>Localization effects 72.15.Rn, Hopping transport 72.20.Ee, Weak localization 73.20.Fz, Spin-density waves<\/p>\n<\/div><\/details><\/div>\n\n\n\n

2010<\/strong><\/p>\n\n\n\n

Origin of the E-2 <-> T-4(2) Fano resonance in Cr3+<\/sup>-doped LiCaAlF6<\/sub>: Pressure-induced excited-state crossover<\/summary>
\n

Author<\/strong>(s):  Sanz<\/strong>-Ortiz, M. N.,Rodriguez,\nFHernandez, I, Valiente, R., Kueck,\nS. <\/p>\n\n\n\n

Source:<\/strong>\nPHYSICAL REVIEW B        Volume:<\/strong> 81          Issue:<\/strong> 4                 Article Number:<\/strong> 045114<\/p>\n\n\n\n

Abstract:<\/strong> This work investigates pressure-induced phase\ntransition (PT) and excited-state-crossover effects on the photoluminescence\n(PL) properties of LiCaAlF6<\/sub>:Cr3+<\/sup>. We report a PL study by\nmeans of time-resolved emission, excitation, and lifetime measurements as a\nfunction of pressure. We focus on Cr3+\n PL variations around pressure-induced trigonal-to-monoclinic first-order PT in LiCaAlF6 at 7 GPa. Moreover, the structural\nrequirements for changing Cr3+ PL\nfrom a broadband emission at 1.59 eV (781 nm) at\nambient conditions, to a rubylike narrow-line\nemission at 1.87 eV (663 nm) are analyzed in the 0-35\nGPa range. We show how\npressure progressively transforms Cr3+ broadband PL into a rubylike\nemission that becomes the dominant feature of the room-temperature emission\nspectrum at 28 GPa. This\nbehavior, together with the pressure dependences of the E-2 and T-4(2)\nexcited-states energy and PL lifetime, are explained on the basis of the\nelectron-phonon coupling associated with the T-4(2) and E-2 states. We\ndemonstrate that both excited states interact through spin-orbit coupling\nyielding Fano resonance rather than antiresonance as is frequently assumed.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHROMIUM PHOTOLUMINESCENCE;\nOPTICAL-PROPERTIES; TRANSITION-METAL; TEMPERATURE-DEPENDENCE;\nELECTRONIC-STRUCTURE; SINGLE-CRYSTALS; LASER MATERIALS; CR3+ IONS;\nSPECTROSCOPY; SPECTRA <\/p>\n\n\n\n

DOI:<\/strong>\n10.1103\/PhysRevB.81.045114 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced switching in a copper(II) citrate dimer<\/summary>
\n

Author(s):<\/strong> Kyle W. Galloway, Stephen A. Moggach, Pascal Parois, Alistair\nR. Lennie, John E. Warren, Euan\nK. Brechin, Robert D. Peacock, Rafael Valiente, Jes\u00fas Gonz\u00e1lez, Fernando Rodr\u00edguez, <\/p>\n\n\n\n

Simon Parsons\nand Mark Murrie<\/p>\n\n\n\n

Source: <\/strong>The\nRoyal Society of Chemistry<\/p>\n\n\n\n

Abstract:\n<\/strong>High pressure single crystal X-ray diffraction\nand high pressure single crystal electronic spectroscopic studies of a copper(II) citrate dimer are\nreported, allowing us to correlate the change in local structure at the Cu(II) centres with the observed piezochromism. <\/strong><\/p>\n\n\n\n

DOI: <\/strong>10.1039\/b000000 [DO NOT ALTER\/DELETE THIS TEXT]<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence of InP\/GaP quantum dots under extreme conditions<\/summary>
\n

Author(s):  <\/strong>Marius Millot ; Sylvie George ; Fariba Hatami ; William T. Masselink ;\nJean Leotin ; Jesus Gonz\u00e1lez\n; Jean-Marc Broto<\/p>\n\n\n\n

Source: <\/strong>High\nPressure Research   Volume:<\/strong> 29    Issue: 4     Pag.: 488\u2013494<\/strong><\/p>\n\n\n\n

Abstract:<\/strong> We present here high-field magneto-photoluminescence experiments on\nself-assembled InP\/GaP quantum dots under high\npressure, at cryogenic temperature. We unveil and discuss a very low pressure\ncoefficient (PC) for the direct exciton and the\nquenching of the strong luminescence at 1.2 GPa. In fact, the magneto-fingerprints, interpreted\nin the classic Fock\u2013Darwin framework, give access to\nthe evolution of charge carriers confinement and\nunravel an increase of the exciton effective mass,\ninvolved in the low effective PC.<\/p>\n\n\n\n

KeyWords<\/strong> Plus: <\/strong>photoluminescence;\nsemiconductors; quantum dots<\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950903399675<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Trigonal field acting at the Cr3+<\/sup> 2<\/sup>E states in ruby from magneto-optical measurements under high pressure<\/summary>
\n

Author(s):  <\/strong>Marius Millot,  Jean-Marc Broto, Jesus Gonzalez, and Fernando Rodr\u00edguez,<\/p>\n\n\n\n

Source: <\/strong>PHYSICAL REVIEW    Volume:<\/strong>\n 81     Pag.:  075120<\/p>\n\n\n\n

Abstract: <\/strong>Magneto-optical measurements on ruby\nunder high-pressure conditions provided direct determination of the trigonal crystal field acting at the t2g<\/sub> orbitals of Cr3+<\/sup> in Al2<\/sub>O3<\/sub> (CrO6<\/sub>)\nand its dependence with pressure. The correlation study between the measured trigonal splitting and the trigonal\ndistortion at the Al3+-<\/sup>substituted site indicates that the trigonal splitting increases with pressure whereas the trigonal distortion slightly reduces. The result is\ninterpreted in terms of an enhancement of the electron-lattice coupling due to trigonal distortion upon reduction in the Al-O bond\ndistance, i.e., the Cr-O bond distance R. The observed variations can be\nexplained on the basis of empirical R dependence of the trigonal\ncrystal field as _Vtr_R\u2212n with n=6. It is shown\nthat this exponent does not change when we consider the pressure variation of\nthe local structure around Cr3+<\/sup> obtained from ab\ninitio calculations. By the way, we also demonstrate that a methanol-ethanol\nmixture is a good pressure transmitting medium at cryogenic temperatures.<\/p>\n\n\n\n

DOI<\/strong>:  10.1103\/PhysRevB.81.075120<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Er3+<\/sup> luminescence as a sensor of high pressure and strong external magnetic fields<\/summary>
\n

Author(s):<\/strong>  R. Valiente, M. Millot, F. Rodr\u00edguez, J. Gonz\u00e1lezc, J.-M. Broto, S.\nGeorge, S. Garc\u00eda-Revilla,Y.\nRomanyuk and M. Pollnau<\/p>\n\n\n\n

Source  <\/strong>High\nPressure Research   Volume:<\/strong> 29    Issue: 4     Pag.: 748\u2013753<\/p>\n\n\n\n

Abstract:<\/strong>\nIn this paper, we present the preliminary results of the combined effect of\nhigh pressure (up to 7.5 GPa) and strong external\nmagnetic fields (up to 28.5 T) on the photoluminescence (PL) properties of\nEr3+\u2013 Yb3+ co-doped single-crystal thin films of well-oriented KY(WO4)2 at low\ntemperatures. Measurements were carried out under pulsed magnetic field,\nexciting the Er3+ ions via upconversion mechanisms by\na Ti:sapphire laser with the\nexternal magnetic field applied along the crystallographic b axis. The detailed\nstudy of the green 4S3\/2 \u2192 4I15\/2 Er3+ PL after infrared excitation\naround 1\u03bcm as a function of pressure and external magnetic field reveals\nthe potential applicability of this system as sensor of high magnetic fields,\nhigh pressure and low temperature, simultaneously.<\/p>\n\n\n\n

Keywords:<\/strong> photoluminescence;\npressure sensor; intense external magnetic field; non-magnetic diamond anvil\ncell<\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950903371716<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Variaci\u00f3n del \u00edndice de refracci\u00f3n de lubricantes (PDV-Supra Premium SJ) bajo altas presiones: <\/strong>contraste de \u00edndice<\/summary>
\n

Author<\/strong>(s): <\/strong>Jes\u00fas Gonz\u00e1lez, Omar Contreras, Chrystian Power y Edgar Belandria<\/p>\n\n\n\n

Source: <\/strong>Scientific\nJournal from the Experimental Faculty of Sciences   Volume:<\/strong>  18 (4)   Pag.:  257 – 264<\/p>\n\n\n\n

Abstract:<\/strong> The\nmotor\u2019s oil multi degree SUPRA SJ SAE 15W 40, is a commercial lubricant of high\nantioxidant protection, elaborated in Venezuela API-SJ certification, for\nengines to petrol, GLP or GNV, with a viscosity to 40\u00b0C of 110 cSt. This study on the variation\nof the refractive index and the viscosity of this lubricant was developed with\na diamond anvil cell, in room temperature, until pressures of 9,2 GPa. Is observed clearly by\nmeans of the variation of the width of line of the luminescence of the ruby (Al2O3:Cr+3) a phase transition of the second order of liquid to glass, in\napproximately 2,25 GPa. Is determine by means of the\ninterferences in the normal transmission and the adjustment of indexes between\nthe lubricant and the grains of ruby, the index of refraction, its dispersion\nwith the energy of the incidental radiation and its variation with the\npressure.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Time-resolved spectroscopy in LiCaAlF6<\/sub> doped with Cr3+<\/sup>: dynamical Jahn\u2013Teller effect and thermal shifts associated with the 4<\/sup>T2 <\/sub>excited state<\/summary>
\n

Author(s): <\/strong>M N Sanz-Ortiz, F Rodr\u00edguez  and R Valiente<\/p>\n\n\n\n

Source: <\/strong>JOURNAL\nOF PHYSICS: CONDENSED MATTER         Volume:<\/strong>  22   Pag.:  125502                                 Online at stacks.iop.org\/JPhysCM\/22\/125502<\/p>\n\n\n\n

Abstract:<\/strong> This\nwork investigates the centre distribution of the Cr3+<\/sup> impurity, the\ndynamical Jahn\u2013Teller effect in the first 4<\/sup>T2<\/sub>\nexcited state and the thermal shifts of the absorption and emission peaks in LiCaAlF6<\/sub>:Cr3+<\/sup>\nby means of time-resolved emission spectroscopy. The electronic and vibrational fine structure observed in both the absorption\nand emission spectra at low temperature are assigned according to the vibrational modes of the internal (CrF6)3\u2212 complex and\nthe lattice modes. Zero-phonon lines associated with 4<\/sup>T2<\/sub> \u21924<\/sup>A2<\/sub>\nand 2<\/sup>E \u21924<\/sup>A2<\/sub> transitions were detected\nand assigned on the basis of available high pressure data in LiCaAlF6<\/sub>:Cr3+<\/sup>.\nWe have identified the vibrational coupled modes\nresponsible for the vibrational structure of the low\ntemperature emission spectrum and the reduction of the zero-phonon line (ZPL)\nsplitting caused by the dynamical Jahn\u2013Teller effect\nin the 4<\/sup>T2<\/sub> excited state (Huang\u2013Rhys factor, Se = 0.92).\nIn addition, from the temperature variation of the emission intensity I (T ), transition energy E(T ) and bandwidth H(T), we obtained\nthe vibrational modes that are coupled to the\nemitting state. We have evaluated the two main contributions to the photoluminescence\nthermal shift through thermal expansion and high pressure measurements: the\nimplicit contribution induced by changes of thermal population and the explicit\ncontribution induced by thermal expansion effects\u201440% and 60% of the total\nshift, respectively<\/p>\n\n\n\n

DOI<\/strong>:  10.1088\/0953-8984\/22\/12\/125502<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Temperature dependence and temporal dynamics of Mn2+<\/sup> upconversion luminescence sensitized by Yb3+<\/sup> in codoped LaMgAl11<\/sub>O19<\/sub><\/summary>
\n

Author(s): <\/strong>R. Mart\u00edn-Rodr\u00edguez, R. Valiente, F. Rodr\u00edguez, F. Piccinelli, A. Speghini and M. Bettinelli<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B                          Volume:<\/strong>  82   Pag.:  075117                                 Online\nat stacks.iop.org\/JPhysCM\/22\/295505<\/p>\n\n\n\n

Spectroscopic study of Cu2+<\/sup> and Cu+<\/sup> ions in high-transmission glass. Electronic structure and Cu2+<\/sup>\/Cu+<\/sup> concentrationsAbstract:<\/strong> A detailed spectroscopic study of the upconversion properties in Mn2+<\/sup>-Yb3+<\/sup> codoped LaMgAl11<\/sub>O19<\/sub> is presented. Pulsed and continuous-wave infrared excitation in the 2<\/sup>F7\/2<\/sub>\u2192<\/em>2<\/sup>F5\/2<\/sub> Yb3+<\/sup> absorption peaks induces broad Mn2+<\/sup> green emission at 19450 cm\u22121<\/sup>, which is assigned to the 4<\/sup>T1<\/sub>\u2192<\/em>6<\/sup>A1<\/sub> transition in tetrahedral Mn2+<\/sup> and sharp peaks associated with Yb3+<\/sup>-pairs luminescence. Both emissions have very different temporal evolution and can be separated by time-resolved spectroscopy. Among the different concentrations under investigation, the 2%Mn2+<\/sup>-5%Yb3+<\/sup> codoped system presents the highest upconversion efficiency. The corresponding emission remains visible to the naked eye up to 650 K. The time dependence of the Mn2+ luminescence upon Yb3+<\/sup> excitation shows distinct behaviors for different doping concentrations. The temporal evolution of the intensity for the diluted system doped with 2%Mn2+<\/sup> and 5%Yb3+<\/sup> together with the pure manganese compound doped with 1%Yb3+<\/sup>, as well as the temperature dependence of the upconversion emission intensity and lifetime are relevant to identify the underlying upconversion mechanisms. We show that the main processes responsible for upconversion in this doubly transition-metal rare-earth doped oxide are both ground-state absorption _GSA_\/excited-state absorption and GSA\/energy-transfer upconversion. An analysis of these processes yielding highly efficient luminescence is discussed on the basis of crystal structure and dopants.<\/p>\n\n\n\n

DOI<\/strong>:  10.1103\/PhysRevB.82.075117<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopic study of Cu2+<\/sup> and Cu+<\/sup> ions in high-transmission glass. Electronic structure and Cu2+<\/sup>\/Cu+<\/sup> concentrations<\/summary>
\n

Author(s): <\/strong>Susana\nGomez, I\u00f1igo Urra, Rafael Valiente  and Fernando Rodriguez<\/p>\n\n\n\n

Source: <\/strong>JOURNAL OF PHYSICS: CONDENSED MATTER\n        Volume:<\/strong>  22   Pag.:  295505                                 Online at stacks.iop.org\/JPhysCM\/22\/295505<\/p>\n\n\n\n

Abstract:<\/strong> This work\ninvestigates the formation of photoluminescence centres\nin high-transmission glass (HTG) doped with Cu2O and their capability to\ntransform the solar spectrum by absorption\/emission via Stokes-shifted PL into\na more efficient spectrum for photovoltaic applications. Among the centres formed in HTG, both green photoluminescent\nCu+ and the non-photoluminescent Cu2+ centres are created but their relative concentration\ndepends on the thermal treatment and the presence of other co-dopants. The measurement of the absorption coefficient \u03b1(<\/em>\u03bb) <\/em>nearby the HTG optical gap for\nCu+ bands is accomplished by following the two-thickness method. This procedure\nallows us to obtain the actual absorption coefficient for the spectrum of each\nformed centre, from which we obtain the relative concentration of Cu+\/Cu2+ as\nwell as their absolute values. The analysis of the spectra provides information\non the absorption cross sections, transition energies and bandwidths, the\nknowledge of which is essential to check the suitability of such centres for photovoltaic applications in solar cells.<\/p>\n\n\n\n

DOI<\/strong>:  10.1088\/0953-8984\/22\/29\/295505<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Raman characterization of carbon materials under non-hydrostatic conditions<\/summary>
\n

Author<\/strong>(s):  E<\/strong>. del Corro, M. Taravillo,\nJ. Gonz\u00e1lez, V.G. Baonza<\/p>\n\n\n\n

Source  <\/strong>Elsevier  C A R B ON                         Pag<\/strong>: 6214<\/p>\n\n\n\n

Abstract:<\/strong> Raman spectroscopy\nexperiments on double-wall carbon nanotube and highly\noriented pyrolytic graphite (HOPG) samples subjected\nto non-hydrostatic conditions have been conducted in anvil cells to study the\neffect of the pressure\/stress on the bands assigned to defects. Typical diamond\nanvils used in high pressure experiments have been substituted by moissanite (6H-SiC) and sapphire (Al2O3) anvils to allow\nthe observation of the D band (around 1350 cm-1) and the second-order Raman\nscattering without interference. We demonstrate that Raman experiments at high\npressure provide unique information to probe the mechanical behaviour\nof carbon materials (CMs). We also show that this can be also a powerful\ntechnique to assign controversial spectral features such as those appearing in\nthe second order region of the spectra of CMs. In HOPG samples we find that the\nD\u00b4\/D band intensity ratio is independent of stress. The results indicate that\nan increase of non-hydrostatic stresses on HOPG generates graphitic domains\nwith sizes around 20-30 nm when the sample is recovered to room conditions.<\/p>\n\n\n\n

.<\/p>\n\n\n\n

DOI: <\/strong>10.1016\/j.carbon.2010.09.064<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure dependence of Raman modes in double wall carbon nanotubes filled with 1D Tellurium<\/summary>
\n

Author<\/strong>(s):  Edgar<\/strong> Belandria, Marius Millot, Jean-Marc Broto, Emmanuel Flahaut,\nFernando Rodriguez, Rafael Valiente, Jesus Gonzalez<\/p>\n\n\n\n

Source  <\/strong>Elsevier  C A R B ON         Volume:<\/strong> 48          Pag: 2 5 6 6 \u20132 5 7 2<\/p>\n\n\n\n

Abstract:<\/strong> The preparation of highly anisotropic one-dimensional (1D)\nstructures confined into carbon nanotubes (CNTs) in\ngeneral is a key objective in nanoscience. In this\nwork, capillary effect was used to fill double wall carbon nanotubes\n(DWCNTs) with trigonal Tellurium. The samples are\ncharacterized by high resolution transmission electronic microscopy and Raman spectroscopy.\nIn order to investigate their structural stability and unravel the differences induced\nby intershell interactions, unpolarized\nRaman spectra of radial and tangential modes of DWCNTs filled with 1D nanocrystalline Te excited with 514 nm were studied at room\ntemperature and high pressure. Up to 11 GPa\nwe found a pressure coefficient of 3.7 cm_1 GPa_1 for the internal tube and 7\ncm_1 GPa_1 for the external tube. In addition, the tangential band of the external and internal tubes broaden and decrease\nin amplitude. All findings lead to the conclusion that the outer tube acts as a\nprotection shield for the inner tube (at least up 11 GPa). No pressure-induced structural phase transition\nwas observed in the studied range.<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.carbon.2010.03.036<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Phonon softening on the specific heat of nanocrystalline metals<\/summary>
\n

Author<\/strong>(s):  D<\/strong> P Rojas, L Fern\u00e1ndez Barqu\u00edn, J Rodr\u00edguez Fern\u00e1ndez, L Rodr\u00edguez Fern\u00e1ndez\nand J Gonz\u00e1lez<\/p>\n\n\n\n

Source  <\/strong>Nanotechnology     Volume:<\/strong> 21          445702(5pp)<\/p>\n\n\n\n

Abstract:<\/strong> Specific\nheat enhancement in several common nanocrystalline\nmetals is established by comparison with their bulk counterparts. Measurements\nwere carried out in Fe, Cu, Ni and binary alloy LaAl2. The\nexcess specific heat is evidenced as a low temperature peak below 65 K and a\nhigh temperature slope above 150 K. The experimental data are in good agreement\nwith a model which considers contributions from the grain boundary and core\natoms in the nanoparticles. This model is supported\nby Raman spectroscopy measurements, showing a softening of the frequency phonon\nmodes associated with a size reduction and increase of the atomic disorder. (Some\nfigures in this article are in colour only in the\nelectronic version)<\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/0957-4484\/21\/44\/445702<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical absorption and Raman spectroscopy of CuWO4<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> J. Ruiz-Fuertes, M. N.\nSanz-Ortiz, J. Gonz\u00e1lez, F. Rodr\u00edguez, A. Segura and D. Errandonea<\/p>\n\n\n\n

Source:<\/strong> Journal\nof Physics: Conference Series           Volume:<\/strong> 215                        Pag<\/strong>:<\/strong> 012048<\/p>\n\n\n\n

Abstract:<\/strong> The\nelectronic absorption and Raman spectra of CuWO4 are studied as a function ofpressure in\nthe 0 \u2013 20 GPa range. The\nbelow-gap absorption bands at 1.15, 1.38 and 1.56 eV correspond\nto Cu2+ d-transitions\nsplit by the Jahn-Teller distortion of CuO6 (R<\/em>eq<\/em> <\/em>= 1.98 \u00c5; R<\/em>ax<\/em> <\/em>=2.39 \u00c5; Qq = 0.47 \u00c5). Pressure induces a strong reduction of the JT\ndistortion up to 10 GPa. Above\nthis pressure we observe, by optical absorption and Raman spectroscopy, a\nfirst-order phase transition at 11 GPa\nwith phase coexistence in the 10-12 GPa range, as it\nis confirmed by Raman spectroscopy. The absorption spectra suggest that two\ndifferent Cu2+ sites are\nformed in the high pressure phase, each having rather different CuO6 distortion. The more JT distorted CuO6 centre is stable up to 20 GPa. Rather than JT reduction, pressure induces\nreorientations of the CuO6 octahedra in the high-pressure\nphase.<\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/1742-6596\/215\/1\/012048<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Doping dependence of the G-band Raman spectra of an individual multiwall carbon nanotube<\/summary>
\n

Author(s):  <\/strong>Sebastien Nanot, Marius Millot, Bertrand Raquet, Jean-Marc Broto, Arnaud Magrez, Jesus Gonzalez<\/p>\n\n\n\n

Source: <\/strong>Physica E Elsevier  Volume<\/strong>:<\/strong>  42     Pag.:  2466\u20132470<\/p>\n\n\n\n

Abstract:<\/strong> We present a gate-dependent\nRaman spectroscopy and electric transport measurements of an individually connected\nmultiwall carbon nanotube in the field-effect transistor\nconfiguration at room temperature. We discuss the origin of the four distinct sharp\nmodes in the G-band feature. The overall G-band is blueshifted\nby tuning the Fermi level under a back-gate voltage. Each mode experiences different\nenergy shifts symmetrical for n\nand p\ndoping. Assuming that the four peaks can be\ntentatively assigned to four different shells of the multiwall carbon nanotube,we propose a simple quantitative\nanalysis which unravels intershell charge transfer within\nthe nanotube.<\/p>\n\n\n\n

DOI<\/strong>:  doi:10.1016\/j.physe.2010.06.006<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Anharmonic effects in ZnO optical phonons probed by Raman spectroscopy<\/summary>
\n

Author(s):<\/strong>  Marius Millot, Ramon Tena-Zaera, Vicente Munoz-Sanjose, Jean-Marc Broto and Jesus Gonzalez<\/p>\n\n\n\n

Source  <\/strong>APPLIED PHYSICS LETTERS          Volume:<\/strong> 96          152103 <\/p>\n\n\n\n

Abstract:<\/strong> We report Raman\nspectroscopy measurements on ZnO crystals grown by\nthe vapor transport method and annealed. Vacuum annealing is found to yield single\ncrystals with ultra low density of defects. We focus on the optical E<\/em>2 phonon\nlinewidth temperature dependence in the 10\u2013500 K\nrange. The linewidth decrease at low temperature is\nanalyzed and discussed in the light of anharmonic up-\nand down-conversion processes, unveiling strongly different behaviors<\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.3387843<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Absorci\u00f3n \u00f3ptica a altas presiones del TLGaSe2<\/sub><\/summary>
\n

Author(s):<\/strong> Ch. Power, I. Molina,\nL. Chac\u00f3n, J. Gonz\u00e1lez, A. Jagui P\u00e9rez-Kuroki y J.C. Chervin<\/p>\n\n\n\n

Source<\/strong>:<\/strong> Revista Mexicana de F\u00edsica             Volume<\/strong>:<\/strong> 56(3)     Issue<\/strong>:<\/strong>                    Pag<\/strong>:<\/strong> 217\u2013222<\/p>\n\n\n\n

Abstract:<\/strong> In this\npaper the spectrum of optical normal transmission not polarized of TlGaSe2 is\nmeasured as a function of pressure up to 27.6 GPa at room temperature. Our results show that in the\nrange of the visible exist the contributions of two direct gaps of energy,\nwhich present a linear dependence with the pressure. The weak transition EA<\/sub>(\u00e8) assigned to the fundamental gap\nof energy, decreases up to 1.5 GPa with a linear coefficien of -5.31x 10-2<\/sup> eVGPa-1<\/sup> and\nthe transition EB<\/sub>(\u00e8) shows a coefficien\nof -9.95 x 10-2<\/sup> eVGPa-1<\/sup> up to 5.3 GPa\n(limit of pressure in the visible spectrum). The results in the infrared do not\nshow the presence of the transition EA allowing to see\nonly the behavior of the second transition rightly up to the pressure of\nmetallization 24.6 GPa. In the range of pressure\nstudied from 0.0 to 27.6 GPa,\nthe transition EB shows a not linear behavior with the pressure of quadratic coefficien 1.83 x10-3<\/sup> eVGPa-2<\/sup>. <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.81.075120 <\/p>\n\n\n\n

Keywords: <\/strong>I-III-VI2 semiconductor;\noptical properties; infrared; high pressure.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

2009<\/strong><\/p>\n\n\n\n

Optical energy gap on zinc-blende CdS nanoparticles under high pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> R. Mart\u00edn-Rodr\u00edguez, R. Valiente, F.\nRodr\u00edguez and J. Gonzalez<\/p>\n\n\n\n

Source:<\/strong> High\nPressure Research     Volume:<\/strong> 29    Issue:\n4     Pag.: 482\u2013487<\/p>\n\n\n\n

Abstract:<\/strong> Yb3+-doped CdS nanoparticles 5 nmin size and\nwith a pure metastable zinc-blende\n(ZB) single phase have been prepared in a planetary ball mill.We\nare in the very weak quantum confinement regime, and therefore the direct\noptical energy gaps of bulk and nanocrystals are similar.\nThe optical absorption edge of CdS nanocrystals is measured as a function of pressure up to 11\nGPa. The direct energy gap\nin the ZB phase increases non-linearly with pressure and the linear pressure\ncoefficient is about 3.2 \u00d7 10\u22122 eV GPa\u22121\nup to 5.5 GPa. When the\npressure is raised above 6GPa, the energy gap drops suddenly by about 0.8 eV and the spectral form of the absorption coefficient is\ntypical of semiconductors with indirect-gap transitions. The solid\u2013solid phase\ntransition from the ZB to the rock-salt phase is observed at pressures far in\nexcess of the bulk phase transition pressure of 3GPa.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> nanocrystals; optical properties; phase transitions<\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950903372615<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n
Synthesis of superparamagnetic iron(III) oxide nanowires in double-walled carbon nanotubesw<\/summary>
\n

Author(s): <\/strong>Carmen-Mihaela T\u0131lmaciu, Brigitte Soula, Anne-Marie Galibert, Petar Lukanov, Lucien Datas, Jes\u00fas Gonz\u00e1lez,\nLuis Fern\u00e1dez Barqu\u00edn, Jes\u00fas Rodr\u00edguez Fern\u00e1ndez, Fernando Gonz\u00e1lez-Jim\u00e9nez,\nJose Jorge and Emmanuel Flahaut<\/p>\n\n\n\n

Source: <\/strong>The\nRoyal Society of Chemistry            Pag<\/strong>:<\/strong> \n6664\u20136666<\/p>\n\n\n\n

Abstract: <\/strong>The synthesis and characterization of superparamagnetic iron(III)\noxide nanowires confined within double-walled carbon nanotubes by capillary filling with a melted precursor\n(iron iodide) followed by thermal  treatment\nis reported for the first time.<\/p>\n\n\n\n

DOI:<\/strong> 10.1039\/b909035e<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopic and luminescence properties of (CH 3<\/sub>)4<\/sub>NMnCl3<\/sub>: a sensitive Mn 2+<\/sup>-based pressure gauge<\/summary>
\n

Author<\/strong>(s):  L<\/strong>. Nataf ; F. Rodr\u00edguez ; R. Valiente ; J. Gonz\u00e1lez<\/p>\n\n\n\n

Source: <\/strong>High\nPressure Research       Volume:<\/strong> 29    Issue:\n4     Pag.: 653\u2013659<\/strong><\/p>\n\n\n\n

Abstract: <\/strong>This work investigates the Mn2+ electronic structure and\nphotoluminescence (PL) in \n[(CH3)4N]MnCl3 (TMMC) and their variation with pressure by\ntime-resolved excitation and emission measurements in the 0\u201315 GPa range.We show that both the crystal-field\nexcitation and the  corresponding PL\nbands experience large pressure redshifts, which are\nassociated with the anisotropic crystal\ncompressibility providing large axial ligand fields\nat the Mn2+ site in TMMC. These variations are very large for the emission\nband, which shifts with pressure at a rate of 21 nm\/GPa\n(50 meV\/GPa), making TMMC suitable for using as a\npressure gauge.We show that TMMC provides precise\npressure determinations in low pressure ranges (MPa\u2013GPa), since it has the capability to detect pressure\nvariations of 10MPa.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> Mn2+; TMMC;\npressure gauge; sensors; photoluminescence; time-resolved spectroscopy<\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950903414979<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Nanocrystals of ZnO formed by the hot isostatic pressure method<\/summary>
\n

Author<\/strong>(s):  J<\/strong>. Gonz\u00e1lez, J. Marquina, F. Rodr\u00edguez and R. Valiente<\/p>\n\n\n\n

 <\/em>Source<\/strong>  <\/em>High<\/em>\nPressure Research<\/em>   <\/em>Volume:<\/strong> 29    Issue:\n4     Pag.: 594\u2013599<\/p>\n\n\n\n

Abstract:  <\/strong>We present here a\nnovel and simple physical method for obtaining ZnO nanocrystals, using the pressure cycle method and the\nmembrane diamond anvil cell (MDAC) up to 13GPa at 500 K. The recovered nanocrystals in the wurtzitic ZnO phase (w-ZnO) were characterized\nby the high-resolution Raman scattering and X-ray diffraction. A single crystal\nof w-ZnO was used in this work. The high-pressure\ncell was a MDAC specifically designed for high-temperature studies. The Raman\nspectra of the high-quality ZnO single crystal and nanocrystals were compared, and we observed both a\nsoftening and an asymmetric broadening of the Raman peaks ,\nwhich are in good agreement with the effect of relaxation of the q-vector selection\nrule due to quantum size confinement effects. The experimental results confirm\nthe existence of ZnO nanocrystals\nin the w-ZnO phase with an average diameter of 17 nm.<\/p>\n\n\n\n

Keywords: <\/strong>nanocrystals; Raman\nscattering; phase transitions; large gap semi-conductors<\/p>\n\n\n\n

DOI<\/strong>:  10.1080\/08957950903417451<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High pressure optical spectroscopy of Ce3+<\/sup>-doped Cs2<\/sub>NaLuCl6<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> Valiente, R, Rodriguez,\nF, Gonzalez, J., Guedel, H.\nU., Martin-Rodriguez, R., Nataf, L., Sanz-Ortiz, M. N., Kraemer,\nK. <\/p>\n\n\n\n

Source:<\/strong> CHEMICAL PHYSICS LETTERS     Volume:<\/strong>\n481        Issue:<\/strong> 1-3             Pages:<\/strong>\n149-151    <\/p>\n\n\n\n

Abstract:<\/strong> The study of the f < > d transition on\nCe3+-doped Cs2NaLuCl6, through the absorption and emission spectra at high\npressure, allows us to conclude that the equilibrium Ce-Cl\nbond distance in the excited state is shorter than in the ground state. The\nobserved band shifts of -530 +\/- 20\n cm (1)\/GPa\nand -415 +\/- 10 cm\n(1)\/GPa in absorption and emission, respectively,\nreveal reduction of the Stokes shift and the spin-orbit interaction with\npressure. (C) 2009 Elsevier B. V. All rights reserved.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ABSORPTION;\nSPECTRA; CE3+ <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.cplett.2009.09.059 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Room-temperature green upconversion luminescence in LaMgAl11<\/sub>O19<\/sub>:Mn2+<\/sup>, Yb3+<\/sup> upon infrared excitatio<\/summary>
\n

Author(s):<\/strong> Martin-Rodriguez, R., Valiente,\nR., Bettinelli, M.<\/p>\n\n\n\n

Source:<\/strong> APPLIED PHYSICS LETTERS         Volume:<\/strong>\n95          Issue:<\/strong> 9                 Article Number:<\/strong> 091913<\/p>\n\n\n\n

Abstract:<\/strong> We present a spectroscopic study of the green upconversion luminescence of Mn2+ upon near infrared Yb3+\nexcitation in LaMgAl11O19 codoped with manganese and\nytterbium. Excitation at 975 nm with a diode laser resonant with the F-2(7\/2)\n–> F-2(5\/2) Yb3+ transition induces a broad emission band centered at 514\nnm and assigned to the T-4(1) –> (6)A(1)\ntransition of tetrahedral Mn2+. The upconversion\nluminescence can be seen by the naked eye up to 500 K. This finding is a promising\nstep in order to use the Mn2+ – Yb3+ system as a potential candidate for\ndisplay phosphors by upconversion. (C) 2009 American\nInstitute of Physics.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> COOPERATIVE LUMINESCENCE; DOPED\nCSMNCL3; SPECTROSCOPY; TRANSITION; MN2+<\/sup> <\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.3220059 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical properties of nanocrystalline-coated Y2<\/sub>O3<\/sub>:Er3+<\/sup>,Yb3+<\/sup> obtained by mechano-chemical and combustion synthesis<\/summary>
\n

Author<\/strong>(s):<\/strong> Martin-Rodriguez, R., Valiente, R., Pesquera, C., Gonzalez, F.,Blanco, C., Potin, V., de Lucas, M. C. Marco<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 129    Issue:<\/strong> 9    Pages:<\/strong> 1109-1114<\/p>\n\n\n\n

Abstract:<\/strong> Y2<\/sub>O3<\/sub>:Er3+<\/sup>, Yb3+<\/sup>\nnanocrystals have been obtained by ball milling and\nusing a combustion synthesis procedure. In both cases the nanocrystals\nhave been successfully coated with SiO2<\/sub> following the Stober method. The average size of the as-synthesized nanoparticles has been estimated from X-ray diffraction\npatterns and transmission electron microscopy images. The dependence of the\noptical properties of these samples on synthesis procedure or dopant concentration has been investigated. Emission,\nexcitation and lifetime measurements have been carried out. Upconversion\nluminescence has been detected in all samples and an enhancement of the red to\ngreen emission ratio has been observed in all samples after infrared compared\nto visible excitation. The mechanisms responsible for the upconversion\nphenomena have been discussed. (C) 2009 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> Nanoparticles;\nUpconversion; Optical properties; Energy transfer;\nCoating <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> UP-CONVERSION; EMISSION<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2009.05.012 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Upconversion Luminescence in Nanocrystals of Gd3<\/sub>Ga5<\/sub>O12<\/sub> and Y3<\/sub>Al5<\/sub>O12<\/sub> Doped with Tb3+<\/sup>-Yb3+<\/sup> and Eu3+<\/sup>-Yb3+<\/sup><\/summary>
\n

Author(s):<\/strong> Martin-Rodriguez, R.,Valiente, R., Polizzi, S.,\nBettinelli, M., Speghini, A.,Piccinelli, F. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICAL CHEMISTRY\nC    Volume:<\/strong>\n113    Issue:<\/strong>\n28    Pages:<\/strong>\n12195-12200     <\/p>\n\n\n\n

Abstract:<\/strong> Gd3Ga5O12 and Y3Al5O12 nanocrystalline\npowders codoped with Yb3+<\/sup> and Tb3+<\/sup>\nor Eu3+<\/sup> have been prepared using the sol-gel Pechini\nmethod. Nanocrystals obtained by this technique\nexhibit a cubic phase with the Ia3 (d) over bar space group,\nParticles show a broad distribution of sizes and shapes, ranging from elongated\nto quasi-spherical particles of tens of nanometers. Optical properties such as\nphotoluminescence and excitation spectra or lifetime measurements have been\nstudied oil these samples. Green\/blue or red visible upconversion\nluminescence from Tb3+<\/sup> D-5(3), D-5(4) -> F-7(J), or Eu3+ D-5(0)\n-> F-7(J) transitions, respectively, has been observed upon Yb3+<\/sup>\nF-2(7\/2) -> F-2(5\/2) excitation at 975 nm. A detailed investigation on the\nspectroscopy and excited state dynamics of these systems is extremely important\nin order to understand the upconversion processes.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> COOPERATIVE ENERGY-TRANSFER; YB3+<\/sup>\nION; NANOPARTICLES; SPECTROSCOPY; EMISSION <\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/jp901711g <\/p>\n<\/div><\/details><\/div>\n\n\n\n

High pressure and high magnetic field behaviour of free and donor-bound-exciton photoluminescence in InSe<\/summary>
\n

Author(s):<\/strong> Millot, M.,\nGilliland, S., Broto, J. M., Gonzalez, J., Leotin, J., Chevy, A., Segura,\nA<\/p>\n\n\n\n

Source:<\/strong> PHYSICA\n STATUS SOLIDI\n B-BASIC SOLID\n STATE\nPHYSICS    Volume:<\/strong>\n246    Issue:<\/strong>\n3    Pages:<\/strong>\n532-535     <\/p>\n\n\n\n

Abstract:<\/strong> We report here first magneto-photoluminescence\ninvestigations under high pressure up to 6 GPa on III-VI layered semiconductor InSe. Both diamagnetism and magnetic field induced gap\nopening driven by Landau quantization became observable by using a 60 T pulsed\nmagnet. The pressure-induced enhancement of the diamagnetic coefficient is\nconsistent with the increase of the dielectric constant under pressure while\nthe evolution of the linear coefficient is consistent with a slight increase of\nthe electron effective mass up to 4 GPa\nand a direct-to-indirect conduction-band crossover around that pressure. (C) 2009\nWILEY-VCH Verlag GmbH & Co. KGaA, Weinheim<\/p>\n\n\n\n

KeyWords Plus:<\/strong> TEMPERATURE; GASE <\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/pssb.200880542 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical characterization of fourfold (T-d)- and sixfold (O-h)-transition-metal species in MgAl2<\/sub>O4<\/sub>:Co2+<\/sub> by time-resolved spectroscopy<\/summary>
\n

Author(s):<\/strong> Nataf, L, Rodriguez, F., Valiente,\nR., Ulanov, V. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 129    Issue:<\/strong> 12    Special Issue:<\/strong> Sp. Iss. SI    Pages:<\/strong>\n1602-1605    Published:<\/strong>\nDEC 2009   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the origin of novel\nvisible photoluminescence (PL) bands observed in the spinel MgAl2<\/sup>O4<\/sup>\nCo2+<\/sup> Besides the well-known fourfold-coordinated Co2+(<\/sup>T-d) PL\nat 670 nm [N V Kuleshov, V.P. Mikhailov, VG. Scherbitsky, RV. Prokoshin and K.V\nYumashev, J Lumin 55 (1993) 265.], a rich structured PL band at 686 nm was also\nobserved that we associate with uncontrolled impurities of sixfold coordinated\nCr3+(<\/sup>O-h)\nby time-resolved spectroscopy and lifetime measurements and their variation\nwith temperature. We also show that the lifetime of the Co2+(<\/sup>T-d) emission\nat 670 nm varies from tau = 6.7 mu s to 780 ns on passing frorn T = 10 to 290\nK. This unexpected behaviour for T-d systems is related to the excited-state\ncrossover (T-4(1)(sic)E-2), making the emission band to transform frorn a\nnarrow-like emission from E-2 at low temperature to a broad structureless band\nfrom T-4(1) at room temperature. (c) 2009 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> Co2+<\/sup>; Cr3+<\/sup>;\nMgAl2<\/sup>O4<\/sup>; Crystal\nfield; Lifetime; Excited state crossover<\/p>\n\n\n\n

KeyWords Plus:<\/strong> SATURABLE ABSORBER; TETRAHEDRAL CO2+<\/sup>;\nSPINEL; IONS; ABSORPTION; CRYSTAL; GLASS <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2008.12.030 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Electronic structure and luminescence of [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnX4<\/sub> (X=Cl,Br) crystals at high pressures by time-resolved spectroscopy: Pressure effects on the Mn-Mn exchange coupling<\/summary>
\n

Author<\/strong>(s):<\/strong> Rodriguez-Lazcano,\nY., Nataf, L., Rodriguez, F.\n<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 80              Issue:<\/strong> 8                 Article Number:<\/strong> 085115   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the Mn2+<\/sup>\nphotoluminescence (PL) and electronic structure of [(CH3<\/sub>)4N]2<\/sub>MnX4<\/sub> (X=Cl,Br)  and their\nvariation with pressure through time-resolved spectroscopy in the 0-15 GPa range. The crystal-field excitation and emission\nspectra are explained on the basis of the MnX42-(T-d) tetrahedra.\nTheir peaks experience large pressure redshifts,\nwhich are associated with the big crystal compressibility and the interaction\nbetween organic\/inorganic ([(CH3<\/sub>)4N]2<\/sub>MnX4<\/sub>\n2-<\/sup>) tetrahedra. The variation in the Racah parameters and crystal-field splitting with pressure\nindicates that the excitation and emission redshifts\nof Mn2+<\/sup> are mainly governed by the increase in the Mn-X bond covalency (70%) rather\nthan the increase in the crystal-field splitting (30%). Above 6 GPa, pressure induces structural modifications, which are\nrelated to aggregation of the MnX4<\/sub>2-<\/sup> tetrahedra\nwith change in Mn2+<\/sup> coordination from fourfold MnX4<\/sub>2-<\/sup>(T-d)\nto sixfold MnX6<\/sub>4-<\/sup>(O-h). This\nprocess involves a drastic change in the PL behavior yielding a simultaneous\ntwo-color PL emission: green emission at 520 nm and a red emission around 650\nnm. Both emissions experience noticeable redshifts\nwith pressure producing a marked piezo-PL effect. The\nlarge pressure range of phase coexistence makes these materials attractive for\nmultiband PL, the wavelengths of which can be tuned through pressure and\neventually stabilized at ambient conditions.<\/p>\n\n\n\n

Author Keywords:<\/strong> angular momentum theory; band\nstructure; bonds (chemical); compressibility; crystal field interactions;\nhigh-pressure effects; organic compounds; photoluminescence; piezo-optical effects; red shift; time resolved spectra <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ONE-DIMENSIONAL LATTICE; HYDROSTATIC-PRESSURE;\nSINGLE-CRYSTAL; MANGANESE(II) COMPOUNDS; OPTICAL-PROPERTIES; EMISSION DYNAMICS;\nPHASE-TRANSITIONS; (CH3)4NMNCL3 TMMC; ROOM-TEMPERATURE; DOPED CRYSTALS <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.80.085115 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure effects on the crystal field and luminescence Stokes shift of Mn2+(<\/sup>Td) in [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnX4<\/sub> (X=Cl,Br) by time-resolved spectroscopy<\/summary>
\n

Author<\/strong>(s):Rodriguez<\/strong>-Lazcano, Y., Nataf,\nLucie, Rodriguez, Fernando<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 29    Issue:<\/strong> 2    Pages:<\/strong> 230-234<\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the Mn2+ electronic\nstructure and photoluminescence (PL) in [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnCl4<\/sub> and [(CH3<\/sub>)4<\/sub>N]2<\/sub>MnBr4<\/sub>\nand their variation with pressure by time-resolved excitation and emission\nspectra in the 0-10GPa range. We show that both the crystal-field excitation\nand corresponding PL bands experience large-pressure redshifts\n(about 5nm\/GPa), which are associated with the high crystal compressibility and\nthe interaction between organic\/inorganic ([CH3<\/sub>]4<\/sub>N-\/MnX[image omitted]) tetrahedra.\nThe energy variation as a function of pressure is explained in terms of the\nisolated Td MnX[image omitted] in the respective crystals through\ncrystal-field models. One salient feature is the reduction of the PL Stokes\nshift with pressure in both crystals as-1.0 and-1.7nm\/GPa for chloride and\nbromide, respectively.<\/p>\n\n\n\n

Author Keywords:<\/strong> Mn2+Td; Oh; crystal field; Stokes\nshift; time-resolved spectroscopy <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> PHOTOLUMINESCENCE; COMPLEXES <\/strong><\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950802564692 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced transformation from isolated MnX4<\/sub>(T-d) to exchange-coupled MnX6<\/sub>(O-h) in A(2)MnX(4) (X: Cl, Br) crystals. Structural correlations by time-resolved spectroscopy<\/summary>
\n

Author(s):<\/strong> Rodriguez-Lazcano, Y., Nataf, L., Rodriguez, F <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 129    Issue:<\/strong> 12    Special Issue:<\/strong> Sp. Iss. SI    Pages:<\/strong> 2000-2003<\/p>\n\n\n\n

Abstract:<\/strong> This work Investigates the Mn2+<\/sup>-photoluminescence\n(PL) of [(CH3<\/sub>)4<\/sub>N-2](2)MnX4<\/sub>\n(X Cl, Br) under high pressure (0-15 GPa). We show that pressure induces\nstructural modifications leading to changes of coordination geometry around\nMn2+ from fourfold-coordinated MnX4<\/sub>2<\/sup> (T-d) to sixfold MnX6<\/sub>4<\/sup>\n(O-h) along with we observe enormous redshifts of the green emission at 520 nm\nas well as a new red emission about 700 nm above 6 GPa. The Mn2+<\/sup>-PL\nbehaviour with pressure in these highly efficient materials is investigated by\ntime-resolved spectroscopy (emission and excitation) Under high pressure\nFurthermore, the two-colour PL emissions induced by pressure experience\nnoticeable redshifts (6 nm\/GPa) producing a marked piezo-PL effect. The large\npressure hysteresis observed in downstroke makes these materials attractive as\na new type for multiband emission, which can be tuned through pressure and\neventually stabilised at ambient conditions. (C) 2009 Elsevier B.V. All rights\nreserved<\/p>\n\n\n\n

Author Keywords:<\/strong> Mn2+<\/sup> T-d\/O-h; High\npressure; Time-resolved spectroscopy; Two-colour luminescence;\nOrganic\/inorganic compounds <\/p>\n\n\n\n

KeyWords Plus:<\/strong> ONE-DIMENSIONAL LATTICE;\nMANGANESE(II) COMPOUNDS; EMISSION DYNAMICS; SINGLE-CRYSTAL; DOPED CRYSTALS;\nTRIBOLUMINESCENCE; PHOTOLUMINESCENCE; LUMINESCENCE; TEMPERATURE; TRANSITIONS<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2009.04.077 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence properties of Jahn-Teller transition-metal ions<\/summary>
\n

Author(s):<\/strong> Sanz-Ortiz, Marta N., Rodriguez,\nFernando<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL\nPHYSICS    Volume:<\/strong>\n131    Issue:<\/strong>\n12  Article<\/strong> Number:<\/strong> 124512 <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the influence of\nelectron-phonon coupling associated with E circle times\ne and T circle times e Jahn-Teller (JT) effect in\ndifferent transition-metal (TM) ions on de-excitation phenomena through nonradiative multiphonon\nrelaxation, i.e., photoluminescence (PL) quenching. We developed a configurational curve model which is able to predict from\nthe absorption spectrum whether a given JT-TM ion is PL or quenched. The\nprediction is made on the basis of an adapted Dexter-Klick-Russell\nparameter for JT systems, defined in terms of spectroscopic parameters through\nLambda(JT) =alpha Delta(abs)(e)\/E-abs, where Delta(abs)(e) refers to the\nsplitting of the parent octahedral E-g states by the JT distortion in E circle\ntimes e (alpha = 3\/4) or T circle times e (alpha = 1\/4), and E-abs is the\nenergy of the first absorption band involving electronic transition between E-g\nand T-2g. We show that PL in any JT-TM ion occurs whenever Lambda(JT)<0.1\nor is quenched if Lambda(JT)>0.2. This result is noteworthy since it allows\nus to establish structural requirements for the JT-TM ion and the host crystal\nto be PL. Although PL properties of materials containing TM ions depend on a\nvariety of structural factors such as the electronic configuration, the site\nsymmetry, and the crystal field produced by neighboring atoms, the present\nmodel achieves this goal through a simple spectroscopic parameter: Lambda(JT). In this work we correlated the PL properties of\ndifferent sixfold-coordinated JT systems such as Ti3+<\/sup>,\nCu2+, Mn3+<\/sup>, Cr2+<\/sup>, Fe2+<\/sup>, Co3+<\/sup>, and\nNi3+<\/sup> in halides and oxides with Lambda(JT)\nobtained from their respective absorption spectra. From this analysis we\nconclude that depending on the nature of the JT coupling and its strength, PL\nis either strongly favored or quenched in T circle times e while it is mostly\nquenched in E circle times e systems due to the larger\nJT distortion. (C) 2009 American Institute of Physics. <\/p>\n\n\n\n

KeyWords Plus:<\/strong> ANGULAR OVERLAP MODEL; CHROMIUM\nPHOTOLUMINESCENCE; OPTICAL-PROPERTIES; LUMINESCENCE PROPERTIES;\nTEMPERATURE-DEPENDENCE; HYDROSTATIC-PRESSURE; CHARGE-TRANSFER; SINGLE-CRYSTAL;\nSPECTROSCOPY; STATES <\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.3223459 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

A-cation effect on the compressibility of ACoF(3) perovskites<\/summary>
\n

Author(s):<\/strong> Aguado, Fernando, Rodr\u00edguez, Fernando, Redfern, Simon A. T.\n<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE\nRESEARCH    Volume:<\/strong> 29    Issue:<\/strong> 4    Pages:<\/strong>\n525-529    Published:<\/strong> 2009   <\/p>\n\n\n\n

Abstract:<\/strong> The aim of this work is to study the\nstructural evolution and stability of ACoF3 (A: K, Rb) <\/p>\n\n\n\n

undistorted perovskites under\nhigh-pressure conditions within the hydrostatic regime (below 10GPa). Attention\nis paid to their distortion propensity, extending the pressure range for this\npurpose. The role of A cations on the crystal compressibility, which can shed\nlight on the mechanism governing the high-pressure evolution of oxides, has\nbeen explored. The results are compared with previous reports on the ABF3 family\nand point out the relevance of d-electron bonding in the crystal\ncompressibility.<\/p>\n\n\n\n

Author Keywords:<\/strong> perovskite; ACoF3; X-ray\ndiffraction; structural distortions; polyhedron compressibility <\/p>\n\n\n\n

KeyWords Plus:<\/strong> HIGH-PRESSURE BEHAVIOR;\nPHASE-TRANSITION; DIFFRACTION; MGSIO3 <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950903468041 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2008<\/strong><\/p>\n\n\n\n

High-pressure behaviour of KMF3<\/sub> perovskites<\/summary>
\n

Author(s):<\/strong> Aguado, Fernando, Rodriguez,\nFernando, Hirai, Shigeto, Walsh, Joanna N., Lennie, Alistair, Redfern, Simon\nA. T. <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong> 539-544 <\/p>\n\n\n\n

Abstract:<\/strong> The structural stability of cubic KMF3<\/sub>\n(M: Mg, Zn, Co, Ni) perovskites has been studied by\npowder X-ray diffraction under pressure. Neither superlattice\nreflections nor peak splitting associated to a phase transition were detected\nin the 0-10GPa pressure range. Furthermore, KMgF3<\/sub> showed no\nstructural changes up to 50GPa. The results were compared with previous reports\non isostructural KMnF3<\/sub>. Tolerance factor\nand site parameters ratio have been analysed as\nhigh-pressure stability indexes for this family of perovskites.<\/p>\n\n\n\n

Author Keywords:<\/strong> perovskite;\nhalides; high pressure; structural stability <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> NEUTRON POWDER DIFFRACTION;\nCRYSTAL-STRUCTURE; KCUF3<\/sub>; KMGF3<\/sub>; KMNF3<\/sub> <\/p>\n\n\n\n

DOI:<\/strong>\n10.1080\/08957950802576464 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Absorption and photoluminescence of Eu2+<\/sup>-doped 1-D CsCdBr3<\/sub> single crystal<\/summary>
\n

Author<\/strong>(s):<\/strong> Garcia-Revilla,\nS., Rodriguez, F., Valiente, R. <\/p>\n\n\n\n

Abstract:<\/strong> Eu2+<\/sup>-doped CsCdBr3<\/sub> single\ncrystals are studied by polarized variable- temperature optical absorption and\nluminescence spectroscopy for different excitation wavelengths. Whereas the\nlow-energy absorption band is assigned to f -> d transitions within Eu2+<\/sup>\nelectronic configuration, the high-energy absorption bands are assigned to Eu-trapped exciton due to the\nproximity of the high-energy d levels to the conduction band. (c) 2007 Elsevier\nB.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> divalent lanthanides; Eu2+; CsCdBr3<\/sub>;\nexciton <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> RARE-EARTH IONS; INORGANIC-COMPOUNDS; EU2+<\/sup>\n<\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2007.12.034\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Temporal dynamics of upconversion luminescence in Er3+<\/sup>, Yb3+<\/sup> co-doped crystalline KY(WO4<\/sub>)(2) thin films<\/summary>
\n

Author(s):<\/strong>\nGarcia-Revilla, S., Valiente, R., Romanyuk,\nY. E., Pollnau, M. <\/p>\n\n\n\n

Source:<\/strong>\nJOURNAL OF LUMINESCENCE    Volume:<\/strong> 128    Issue<\/strong>:<\/strong> 5-6    Pages:<\/strong>\n934-936    Published:<\/strong>\nMAY-JUN 2008   <\/p>\n\n\n\n

Abstract:<\/strong>\nCrystalline Er3+ and Yb3+ singly and doubly doped KY(WO4<\/sub>)(2)\nthin films were grown by low-temperature liquid-phase epitaxy.\nAbsorption, luminescence, excitation and temporal evolution measurements were carried\nout for both Er3+ and Yb3+ transitions from 10 K to room temperature. Green\nEr3+ upconversion luminescence was observed after\nYb3+ and Er3+ excitation. The mechanisms responsible for the upconversion phenomena detected in each case were\nidentified. (c) 2007 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> upconversion; KY(WO4<\/sub>)(2<\/sub>);\nEr3+<\/sup>; Yb3+<\/sup>; thin films <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> LASER <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2007.12.025 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure dependence of Raman modes in double wall carbon nanotubes filled with \u2013Fe<\/summary>
\n

Author(s):<\/strong> Gonzalez, J., Power, C, Belandria,\nE., Jorge, J., Gonzalez-Jimenez, F., Millot, M., Nanot, S., Broto, J. M., Flahaut, E.<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong> 577-582   <\/p>\n\n\n\n

Abstract:<\/strong> The preparation of highly anisotropic\none-dimensional (1D) structures confined into carbon nanotubes\n(CNTs) in general is a key objective in CNTs research. In this work, the capillary effect was used\nto fill double wall carbon nanotubes with iron. The\nsamples are characterized by Mossbauer and Raman spectroscopy, transmission\nelectron microscopy, scanning area electron diffraction, and magnetization. In\norder to investigate their structural stability and compare it with that of\nsingle wall carbon nanotubes (SWNTs),\nelucidating the differences induced by the inner-outer tube interaction, unpolarized Raman spectra of tangential modes of double\nwall carbon nanotubes (DWNTs)\nfilled with 1D nanocrystallin -Fe excited with 514 nm\nwere studied at room temperature and elevated pressure. Up to 16GPa we find a\npressure coefficient for the internal tube of 4.3cm-1GPa-1 and for the external\ntube of 5.5cm-1GPa-1. In\naddition, the tangential band of the external and internal tubes broadens and\ndecreases in amplitude. All findings lead to the conclusion that the outer tube\nacts as a protection shield for the inner tubes (at least up 16GPa). Structural\nphase transitions were not observed in this range of pressure.<\/p>\n\n\n\n

Author Keywords:<\/strong> carbon nanotubes;\nRaman scattering; high pressure <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> NANOWIRES; MOSSBAUER; ELECTRON <\/p>\n\n\n\n

DOI:<\/strong>\n10.1080\/08957950802485757<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Room-temperature photoluminescence in MnF2<\/sub> under high pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> Hernandez,\nI., Rodriguez, F, Hochheimer,\nH. D. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 128    Issue:<\/strong> 5-6    Pages:<\/strong> 1007-1009   <\/p>\n\n\n\n

Abstract:<\/strong> A novel two-color photoluminescence (PL) is\nfound in MnF2<\/sub> at room temperature (RT) under high pressure. In\ncontrast to the low-temperature PL, the observation of room-temperature PL is\nunusual in transition-metal concentrated materials like MnF2<\/sub> since\nthe de-excitation process at RT is fully governed by energy transfer to non-radiative centers. We show that room-temperature MnF2<\/sub>\nemissions originate in the pressure-induced cotunnite\nphase. Both the nine-fold Mn2+<\/sup> coordination and the Mn-F-Mn exchange pathway inhibit exciton\nmigration among Mn2+<\/sup> favoring two-band PL at RT. The electronic\nstructure and the excited-state dynamics are investigated by time-resolved\nemission and excitation spectroscopies under\npressure. The two PL bands at 2.34 and 1.87eV above 15 GPa are assigned to Mn2+ emissions arising from two\ndistinct Mn2+<\/sup> centers formed in the MnF2 high-pressure phase. The\nmicroscopic origin of the two-color PL is analyzed in terms of exciton dynamics in the MnF2<\/sub> cotunnite\nstructure. (C) 2007 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> MnF2; high-pressure; time-resolved\nspectroscopy; energy transfer <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2007.10.030 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical Properties of the (CrF6<\/sub>)3-<\/sup> Complex in A(2)BMF(6<\/sub>):Cr3+<\/sup> Elpasolite Crystals: Variation with M-F Bond Distance and Hydrostatic Pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> Hernandez,\nIgnacio, Rodriguez, Fernando, Tressaud,\nAlain <\/p>\n\n\n\n

Source:<\/strong> INORGANIC CHEMISTRY    Volume:<\/strong> 47    Issue:<\/strong> 22    Pages:<\/strong> 10288-10298   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the photoluminescence\n(PL) properties of the Cr3+<\/sup>-doped and Cr3+<\/sup>-pure fluoroelpasolites along the A(2)BMF(6)\nseries and as a function of pressure. In particular, we focus on the variation\nof the crystal-field spectrum and the associated PL. The results are explained\non the basis of the octahedral (CrF6<\/sub>)(3-)\ncomplex subjected either to external pressure or the internal pressure exerted\nby different crystal hosts. We have established structural correlations between\nthe crystal-field parameter 10Dq and the Cr-F distance, RCr-F,\nfrom which we have determined the local structure around the Cr3+ impurity,\nallowing the host material effect on the Cr-F bonds to be studied. As salient\nfeatures, we show, first, a weak dependence of the first excitation energy, El,\nusually identified as 10Dq, with RCr-F as E-1 =\nKRCr-F-3.3 and, second, an increase of the Stokes shift upon RCr-F reduction or with increasing pressure. We associate\nthis unusual behavior with the existence of state mixing among T-4(2g)(F), E-2(g)(G), and T-2(1g)(G) states in the first\nexcitation band of Cr3+.<\/sup> Finally, high-pressure experiments\nperformed on Rb2<\/sub>KCrF6<\/sub> indicate that the excited-state\nspin crossover, E-2(g)(G) <-> T-4(2g)(F), takes\nplace around 7 GPa. The results indicate the\nsuitability of the selected A(2)BMF(6):Cr3+ elpasolites to establish structural correlations between PL\nand RCr-F.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> NEAR-INFRARED LUMINESCENCE; D-D SPECTRUM;\nCHROMIUM PHOTOLUMINESCENCE; TEMPERATURE-DEPENDENCE; TRANSITION-METAL;\nSINGLE-CRYSTALS; ELECTRONIC-STRUCTURE; ABSORPTION-SPECTRA; FLUORIDE LATTICES;\nCr3+<\/sup> IONS <\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/ic800606h<\/p>\n<\/div><\/details><\/div>\n\n\n\n

High-field Zeeman and Paschen-Back effects at high pressure in oriented ruby<\/summary>
\n

Author(s):Millot<\/strong>,\nMarius ,Broto, Jean-Marc, Gonzalez, Jesus<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 78    Issue:<\/strong> 15  Article<\/strong> Number:<\/strong>\n155125    <\/p>\n\n\n\n

Abstract:<\/strong> High-field Zeeman and Paschen-Back\neffects have been observed in single crystals of ruby submitted to hydrostatic\npressure up to 10 GPa. A\nspecific setup with a miniature diamond-anvil cell has been developed to\ncombine high pressure and pulsed magnetic fields and to perform magnetophotoluminescence measurements. Careful analysis of\nlow-temperature (4.2 and 77 K) photoluminescence spectra with a 56 T magnetic\nfield applied along the c axis allows for the rectification of the assignment\nof observed emission lines to corresponding Zeeman-split levels. Besides, the\nintrinsic Zeeman-splitting factors of excited states reveal a linear\npressure-induced increase. This enhancement is a signature of an increase in trigonal distortion induced by hydrostatic pressure.\nMoreover, spectra with magnetic field perpendicular to crystallographic c axis\nexhibit a Paschen-Back effect reflecting the\nprogressive alignment of Cr3+<\/sup> ions spin along the applied field.\nHowever, no pressure modification is observed in this compound,\ncontrarily to the Heisenberg-to-Ising spin character\npressure-induced transition observed in alexandrite.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> DIAMOND-ANVIL CELL; HIGH MAGNETIC-FIELDS;\nABSORPTION SPECTRA; LINE SHIFTS; R-LINES; AL2O3<\/sub>; Cr-3<\/sup>;\nKBAR <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.78.155125<\/p>\n<\/div><\/details><\/div>\n\n\n\n

New diamond anvil cell for optical and transport measurements under high magnetic fields up to 60T<\/summary>
\n

Author(s):<\/strong> Millot, Marius, George,\nSylvie, Broto, Jean-Marc, Couzinet,\nBernard, Chervin, Jean-Claude, Polian,\nAlain, Power, Chrystian, Gonzalez, Jesus<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong> 627-631<\/p>\n\n\n\n

Abstract:<\/strong> We present here a new diamond anvil cell\ndesigned to combine high hydrostatic pressure up to 10GPa, non-destructive,\npulsed magnetic fields up to 60T and low temperature as low as 2K. Both optical\nand transport measurements are now achievable. Magneto-photoluminescence set-up\nunder pressure is described in great detail. We report photoluminescence\nexperiments on oriented ruby single crystals exhibiting direct observation of\nthe intrinsic Zeeman splitting of excited states under pressure.<\/p>\n\n\n\n

Author Keywords:<\/strong> high pressure; high magnetic field;\nluminescence; diamond anvil cell; ruby <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong>\nSUPERCONDUCTIVITY <\/p>\n\n\n\n

DOI:<\/strong>\n10.1080\/08957950802510554 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence of MgAl2<\/sub>O4<\/sub>:Co2+<\/sup>through time-resolved spectroscopy under pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> Nataf, Lucie, Rodriguez, Fernando, Valiente,\nRafael <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong>\n553-558     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the Co2+(<\/sup>Td) electronic structure and photoluminescence\n(PL) in MgAl2O4:Co2+ and their variation with pressure by time-resolved\nspectroscopy. The absorption spectra and the pressure and temperature dependences\nof the emission band at 663nm (=120ns, at ambient conditions) can be explained\non the basis of a configurational energy model, which\nprovides an interpretation of the electronic structure and the excited-state\nphenomena. We show that there is an excited-state crossover [4T 1(P)2E (G)] at\nambient pressure, which is responsible for the evolution of the emission\nspectrum from a broadband emission between 300 and 100K to a narrow-peak\nemission at 6K. The pressure, instead of enhancing excited-state crossover\nphenomena, reduces PL and suppresses it (PL quenching) above 6GPa. We explain\nsuch variations in terms of pressure-induced non-radiative\ncrossover relaxation to lower excited states: 2E (G)4T\n1(F). The variation of PL intensity and its associated lifetime with pressure\nsupports the proposed interpretation.<\/p>\n\n\n\n

Author Keywords:<\/strong> Co2+<\/sup>Td; MgAl2<\/sub>O4<\/sub>;\nexcited-state crossover; time-resolved spectroscopy <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> SATURABLE ABSORBER; TETRAHEDRAL CO2+<\/sup>;\nMGAL2<\/sub>O4<\/sub>; ABSORPTION; CRYSTAL; SPINEL; GLASS; IONS <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950802510562<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spin transition in Co3+<\/sup>by optical absorption and time-resolved spectroscopy under pressure: an appraisal of the different spin states<\/summary>
\n

Author<\/strong>(s):<\/strong> Sanz-Ortiz, Marta N., Rodriguez, Fernando, Demazeau,\nGerard <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong>\n571-576     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the electronic structure\nof CoF3 by optical absorption and its relationship with the ground-state spin\nand the Jahn-Teller (JT) effect exhibited by Co3+(d6)\nin octahedral coordination (CoF6<\/sub>)3-<\/sup>. The results are\ncompared with other Co3+<\/sup> fluorides and oxides, where Co3+ is high\nspin (HS) and low spin (LS), respectively. In CoF3 we detect an absorption band\nwith a doublet structure at 1.89eV (657nm) and 1.45eV (855nm) at 2.5GPa, which\nis associated with the T e JT effect on the 5T2 HS ground state. Absorption\nmeasurements under pressure have been carried out around the HS-LS (5T2 1A1)\nspin crossover transition in the 0-20 GPa\nrange. We show that the JT effect is stable in a wide pressure range. No sign\nof intermediate spin (3T1, 2 states) is observed in the explored pressure\nrange.<\/p>\n\n\n\n

Author Keywords:<\/strong> Co3+<\/sup>; CoF3<\/sub>;\nspin crossover; intermediate spin; Jahn-Teller <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950802552119 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Time-resolved spectroscopy in LiCaAlF6 doped with Cr3+<\/sup> as a function of pressure and temperature – Excited-state crossover and phase-transition effects<\/summary>
\n

Author<\/strong>(s):<\/strong> Sanz-Ortiz, M. N., Rodriguez, F., Hernandez, I.,\nValiente, R., Kueck, S. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 128    Issue:<\/strong> 5-6    Pages:<\/strong> 721-724     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates phase transition (PT)\nand excited-state-crossover (ESCO) effects on the\nphotoluminescence (PL) properties of LiCaAlF6:Cr3+<\/sup>. The structural\nrequirements for changing the Cr3+\n <\/sup>PL behavior from a broad-band emission at\n1.59eV (781 nm) at ambient conditions, to ruby-like narrow-line emission at\n1.87eV (663 nm) are analyzed in the 0-35 GPa\nrange. We report a PL study on LiCaAlF6<\/sub>:Cr3+<\/sup> by means of\ntime-resolved emission as a function of pressure and temperature. In particular\nwe focus on the PL variations occurring around the pressure-induced trigonal-to-monoclinic first-order PT in LiCaAlF6<\/sub>\nat 7 GPa. (C) 2007 Elsevier\nB.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> LiCaAlF6; Cr3+; high-pressure;\ntime-resolved spectroscopy; excited state crossover <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2007.10.027 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Room-temperature photoluminescence in MnF2<\/sub> under high pressur<\/summary>
\n

Author<\/strong>(s):<\/strong> Hernandez,\nI., Rodriguez, F, Hochheimer,\nH. D. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 128    Issue:<\/strong> 5-6    Pages:<\/strong> 1007-1009   <\/p>\n\n\n\n

Abstract:<\/strong> A novel two-color photoluminescence (PL) is\nfound in MnF2<\/sub> at room temperature (RT) under high pressure. In\ncontrast to the low-temperature PL, the observation of room-temperature PL is\nunusual in transition-metal concentrated materials like MnF2<\/sub> since\nthe de-excitation process at RT is fully governed by energy transfer to non-radiative centers. We show that room-temperature MnF2<\/sub>\nemissions originate in the pressure-induced cotunnite\nphase. Both the nine-fold Mn2+<\/sup> coordination and the Mn-F-Mn exchange pathway inhibit exciton\nmigration among Mn2+<\/sup> favoring two-band PL at RT. The electronic\nstructure and the excited-state dynamics are investigated by time-resolved\nemission and excitation spectroscopies under\npressure. The two PL bands at 2.34 and 1.87eV above 15 GPa are assigned to Mn2+ emissions arising from two\ndistinct Mn2+<\/sup> centers formed in the MnF2 high-pressure phase. The\nmicroscopic origin of the two-color PL is analyzed in terms of exciton dynamics in the MnF2<\/sub> cotunnite\nstructure. (C) 2007 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> MnF2; high-pressure; time-resolved\nspectroscopy; energy transfer <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.jlumin.2007.10.030 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Raman spectra of double-wall carbon nanotubes under extreme uniaxial stress<\/summary>
\n

Author<\/strong>(s):<\/strong> del Corro, Elena, Gonz\u00e1lez, Jes\u00fas, Taravillo, Mercedes, Flahaut,\nEmmanuel, Baonza, Valent\u00edn G. <\/p>\n\n\n\n

Source:<\/strong> NANO LETTERS    Volume:<\/strong> 8    Issue:<\/strong> 8    Pages:<\/strong> 2215-2218     <\/p>\n\n\n\n

Abstract:<\/strong> We investigated the pressure dependence of the\nRaman frequencies and intensities of the D and G bands of double-wall carbon nanotubes under strong uniaxial\nconditions. Using moissanite anvils, we observed for\nthe first time the evolution of the D band under extreme stress\/pressure\nconditions. We find that the difference between D and G frequencies remains\nconstant over the whole stress range. In addition, we observe that double-wall\ncarbon nanotubes behave elastically up to the maximum\nuniaxial stress reached in our experiments, which is\nestimated to be about 12 GPa.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> HIGH-PRESSURE; SPECTROSCOPY; SCATTERING; BUNDLE\n<\/p>\n\n\n\n

DOI:<\/strong> 10.1021\/nl080760o <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Graphite under non-hydrostatic conditions<\/summary>
\n

Author<\/strong>(s):<\/strong> del Corro, Elena, Gonzalez, Jesus, Taravillo, Mercedes, Escoffier,\nWalter, Baonza, Valentin G.<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 28    Issue:<\/strong> 4    Pages:<\/strong>\n583-586     <\/p>\n\n\n\n

Abstract:<\/strong> The combination of Raman spectroscopy and\nhigh-pressure techniques provides a unique method for studying the mechanical\nand structural response of carbon-based materials. Existing Raman studies on\ngraphite under pressure were restricted to the analysis of the so-called G\nband, because the Raman signal from the diamond anvils overlaps other\ncharacteristic Raman features, like the D band. Here, we present a Raman\nspectroscopy study of highly oriented pyrolytic\ngraphite (HOPG) under uniaxial stress using moissanite anvils. The use of moissanite\nhas allowed us to observe, for the first time, the evolution of the D band\nunder extreme compression. We have employed several excitation wavelengths:\n632.8, 532.0 and 488.0nm, to further study dispersion effects. Our results have\nimportant implications on the interpretation of high-pressure Raman results on\nseveral families of carbon-based compounds.<\/p>\n\n\n\n

Author Keywords:<\/strong> highly oriented pyrolytic\ngraphite; Raman spectroscopy; uniaxial stress; moissanite anvil cell <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> RAMAN;\n1ST-ORDER; PRESSURE <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950802444796 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2007<\/strong><\/p>\n\n\n\n

Pressure-induced Jahn-Teller suppression and simultaneous high-spin to low-spin transition in the layered perovskite CsMnF4<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> Aguado, Fernando, Rodriguez, Fernando, Nunez, Pedro\n<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 76    Issue:<\/strong> 9  Article<\/strong> Number:<\/strong>\n094417     <\/p>\n\n\n\n

Abstract:<\/strong> The interplay between the orbital ordering and\nthe spin state in Jahn-Teller Mn3+<\/sup>\ngoverning the optical, magnetic, and transport properties in the layered CsMnF4<\/sub>\nperovskite is investigated. Such electronic effects\nare strongly coupled to the lattice and thus can be modified by external\npressure. However, there is very little understanding of the structural\nconditions which are required to attain spin crossover in connection with the\nelectronic structure of Mn3+.<\/sup> The distortion, spin state, and\ntilting of (MnF6)(3-) octahedra\nin the insulating ferromagnet CsMnF4 <\/sub>are\njointly studied by high-pressure optical spectroscopy. The insulating character\nof CsMnF4<\/sub> allowed us to explore the electronic structure associated\nwith the 3d levels of Mn3+ in the 0-46 GPa\npressure range, an information which is obscured in most oxides due to\nmetallization at high pressure. We show that the spin-crossover transition,\nrelated to the spin change, S = 2 -> 1, in Mn3+, takes place at 37 GPa with the simultaneous suppression of the axially\nelongated distortion associated with the Jahn-Teller\neffect. The wide stability pressure range of the Jahn-Teller\ndistortion and high-spin state is explained in terms of crystal-field models\nincluding the Jahn-Teller stabilization energy. On\nthis basis, we discuss the interplay between spin transition and Jahn-Teller effect comparing present findings with other\nresults attained in Mn3+, Ni3+, and Co3+ systems.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong>\nOPTICAL-PROPERTIES; METAL-INSULATOR; LOWER MANTLE; STATE; NI3+ <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.76.094417 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Variation of the Jahn-Teller distortion with pressure in the layered perovskite Rb2<\/sub>CuCl4<\/sub>: local and crystal compressibilities<\/summary>
\n

Author(s):<\/strong> Aguado, F., Rodriguez, F., Valiente,\nR., Hanfland, M., Itie, J. P. <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n19    Issue:<\/strong>\n34  Article<\/strong> Number:<\/strong>\n346229     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the effect of pressure\non the Jahn-Teller distortion (JTD) associated with the axially elongated CuCl6\noctahedra in the A(2)CuCl(4) perovskite layer (A: Rb,\nCH3NH3, C2H5NH3, C3H7NH3). The aim is to elucidate whether pressure favours\ndisappearance of the JTD in the antiferrodistortive (AFD) structure exhibited\nby Cu2+ within the layers or whether it induces tilts of the CuCl6 octahedra\npreserving the molecular distortion associated with the JT effect. We have\ncarried out x-ray absorption (XAS) and x-ray diffraction (XRD) experiments\nunder pressure along the compound series, whose interlayer distances at ambient\npressure vary from 7.77 to 12.33 angstrom. The use of both XAS and XRD\ntechniques allows us a complete local- and crystal-structure characterization\nin Rb2CuCl4 as a function of pressure in the 0-16 GPa\nrange. We show that pressure reduces the axial (long) and equatorial (short)\nCu-Cl distances, R-ax and R-eq, as well as the intralayer and interlayer Cu-Cu\ndistances, d(Cu-Cu) and d(inter). Interestingly, the\nvariation of R-ax is an order of magnitude bigger than that of the\ncorresponding R-eq, yielding a reduction of the JTD. However, no evidence of\nJTD suppression has been observed below 16 GPa.\nPressure-induced CuCl6 tilting preserves the JTD in a wide pressure range.\nEstimates based on structural data suggest that JT suppression would occur at\nabout 40 GPa.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> NEUTRON-SCATTERING MEASUREMENTS;\nHEISENBERG-FERROMAGNET K2CUF4; MAGNETIC-SUSCEPTIBILITY; POWDER DIFFRACTION;\nCHARGE-TRANSFER; TRANSITION; (C2H5NH3)(2)CUCL4;\nDISAPPEARANCE; MOMENT; SERIES <\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/0953-8984\/19\/34\/346229 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopic study of milled MnF2<\/sub> nanoparticles. Size-and-strain-induced photoluminescence enhancement<\/summary>
\n

Author(s):<\/strong> Hernandez, Ignacio; Rodriguez, Fernando<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n19    Issue:<\/strong>\n35  Article<\/strong> Number:<\/strong>\n356220     <\/p>\n\n\n\n

Abstract:<\/strong> This work presents a correlated structural and\nspectroscopic study on ball-milled MnF2<\/sub>. The aims are to produce\nimpurity-lean particles through particle-size reduction leading to\nroom-temperature photoluminescence (PL) and to modify the electronic states of\nthe emitting centres. Despite non-radiative\ncentres being still present, the PL quenching\ntemperature was increased nearly 80 K, from 120 to 200 K, following this method. Milled MnF2<\/sub> has particle sizes down to\nseveral nanometres, and structural changes from the\ninitial alpha-TiO2<\/sub> structure to the alpha-PbO2<\/sub> phase.\nMilling favours the presence of adsorbed water on the\nnanoparticle surface. Time-resolved spectroscopy\nindicates that the nanoparticle PL consists of a\nsignificantly inhomogeneous broadened band with respect to the initial MnF2<\/sub> PL.\nThe temperature dependence of the lifetime measured at different wavelengths of\nthe emission spectrum indicates the presence of several PL centres,\nthe population of which is controlled by exciton\nmigration and trapping. The widespread occurrence of emitting centres is explained in terms of milling-induced strains,\nthe coexistence of two different structural phases, and the presence of\nadsorbed water molecules.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ENERGY-TRANSFER; MAGNETIC-STRUCTURE;\nCRYSTALS; FLUORESCENCE; LUMINESCENCE; IONS; TEMPERATURE; TRANSITIONS; PRESSURE <\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/0953-8984\/19\/35\/356220 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced two-color photoluminescence in MnF2<\/sub> at room temperature<\/summary>
\n

Author<\/strong>(s):<\/strong> Hernandez,\nI., Rodriguez, Fernando, Hochheimer,\nH. D.<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW LETTERS    Volume:<\/strong> 99    Issue:<\/strong> 2  Article<\/strong> Number:<\/strong>\n027403     <\/p>\n\n\n\n

Abstract:<\/strong> A novel two-color photoluminescence (PL) is\nfound in MnF2 at room temperature under high pressure. Contrary to\nlow-temperature PL, PL at room temperature is unusual in transition-metal\nconcentrated materials like MnF2, since the deexcitation\nprocess at room temperature is fully governed by energy transfer to nonradiative centers. We show that room-temperature PL in\nMnF2 originates from two distinct Mn2+ emissions in the high-pressure cotunnite phase. The electronic structure and the\nexcited-state dynamics are investigated by time-resolved emission and\nexcitation spectroscopy at high pressure.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ENERGY-TRANSFER; OPTICAL SPECTROSCOPY;\nCRYSTALS; FLUORESCENCE; LUMINESCENCE; IONS; SYSTEMS; MN-2+; KMGF3; LASER <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevLett.99.027403 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Variation of the Jahn-Teller distortion with pressure in perovskite layers A(2)CuCl(4). Influence on the charge-transfer ban<\/summary>
\n

Author(s):<\/strong> Rodriguez, F., Aguado, F, Valiente, R.,\nHanfland, M.,Itie, J. P. <\/p>\n\n\n\n

Source:<\/strong> PHYSICA\n STATUS SOLIDI\n B-BASIC SOLID\n STATE\nPHYSICS    Volume:<\/strong>\n244    Issue:<\/strong>\n1    Pages:<\/strong>\n156-161     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the variation of the\nfirst charge-transfer (CT) transition with pressure in the A(2)CuCl(4) layered perovskites, in\nterms of structural changes, in particular, the local structure of the\n(CuCl6)(4-) octahedra. We show that pressure\npartially reduces the Jahn-Teller distortion. The\ndecrease of the axial Cu-Cl distance, R-ax, is an\norder of magnitude bigger than the decrease of the equatorial distance, R-eq, but the in-plane Cu-Cu distance reduction is almost\ntwice that the sum of R-ax and R-eq, thus indicating\npressure-induce tilts. This phenomenon avoids suppression of the JT effect,\nkeeping the (CuCl6)(4-) axial distortion above 10 GPa. Both the partial reduction of the JT distortion and tiliting can account for the CT redshift\ninduced by pressure. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> STRUCTURAL CORRELATIONS; HYDROSTATIC-PRESSURE;\nCU2+; (C2H5NH3)(2)CDCL4CU2+; SPECTROSCOPY; SPECTRA;\nSYSTEMS <\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/pssb.200672506 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Red-to-yellow pressure-induced phase transition in Pt(bpy)Cl-2<\/sup>: Spectroscopic study supported by DFT calculations<\/summary>
\n

Author(s): <\/strong>Valiente,\nRafael, Garcia-Lastra, Juan M. ,\nGarcia-Fernandez, Pablo, Garcia-Revilla, Sara, Wenger, Oliver S. <\/p>\n\n\n\n

Source:<\/strong> EUROPEAN JOURNAL OF INORGANIC\nCHEMISTRY    Issue:<\/strong>\n36    Pages:<\/strong>\n5735-5742     <\/p>\n\n\n\n

Abstract:<\/strong> The combination of spectroscopic and\ncomputational methods has been employed to explore the origin of the\nluminescence in the red and yellow forms of Pt(bpy)Cl-2. The luminescence of the red (linear-chain) form\nof Pt(bpy)Cl-2 (bpy 2,2′-bipyridine) has been measured as a function of\nhydrostatic pressure up to 65 kbar. The luminescence\nband maximum is redshifted (-147 cm(-1) kbar(-1)), and the intrachain Pt-Pt distance decreases from 3.46 to 3.25\nangstrom between ambient pressure and 17.7 kbar.\nStrong discontinuities in the optical properties at 17.7 kbar\nwere interpreted in terms of a crystallographic phase transition from the red\nto a denser yellow form of Pt(bpy)Cl-2.\nFirst-principles calculations based on density functional theory were used to\nstudy the red to yellow phase transformation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451\nWeinheim,\n Germany, 2007).<\/p>\n\n\n\n

Author Keywords:<\/strong> phase transition; high-pressure\nchemistry; DFT calculations; platinum(II); metal-metal\ninteractions <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ALPHA-DIIMINE LIGANDS; PLATINUM(II) COMPLEXES;\nELECTRONIC-SPECTRA; EXCITED-STATES; SQUARE-PLANAR; LUMINESCENCE; DENSITY;\nPHOTOPHYSICS; DEPENDENCE; ENERGIES <\/p>\n\n\n\n

DOI:<\/strong> 10.1002\/ejic.200700060 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2006<\/strong><\/p>\n\n\n\n

Jahn-Teller effect under pressure<\/summary>
\n

Author(s):<\/strong> Aguado, F., Rodriguez, F.<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 26    Issue:<\/strong> 4    Pages:<\/strong> 319-323 <\/p>\n\n\n\n

Abstract:<\/strong> This work deals with structural correlation\nstudies in Jahn-Teller (JT) systems of Cu2+ and Mn3+\nin the layer perovskites A(2)CuCl(4)\nand AMnF(4). The aim is to explore the influence of\nthe JT effect on the materials’ properties as well as its variation with\npressure. We present structural studies carried out in the layer perovskites AMnF(4) by optical\nspectroscopy under pressure in order to explore whether pressure reduces the JT\ndistortion or induces tilting phenomena of the JT octahedra\n(MnF6)(3-). The influence of the JT effect on the stabilization of the\nground-state spin, either high-spin (HS) or low-spin (LS), in Mn3+ is analyzed.\nThis knowledge is important to understand and, eventually predict, magnetic,\nelectrical and optical properties in connection with HS-LS phenomena. The\nresults are compared with previous structural studies performed in the (CuCl6)(4-) JT octahedra formed in A(2)CuCl(4).<\/p>\n\n\n\n

Author Keywords:<\/strong> Mn3+; CU2+; Jahn-Teller\neffect; spectroscopy under pressure; layer perovskite\n<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> TRANSITION <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950601104427 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

-d transitions and self-trapped excitons in CsCdBr3 : Eu2+<\/sup><\/summary>
\n

Author(s):<\/strong> Garcia-Revilla, S., Valiente, R.<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n18    Issue:<\/strong>\n49    Pages:<\/strong>\n11139-11148    <\/p>\n\n\n\n

Abstract:<\/strong> Single crystals of CsCdBr3 doped with Eu2+ at\ndifferent concentrations were grown by the Bridgman technique and studied by\npolarized variable-temperature optical absorption and luminescence spectroscopy\nfor different excitation wavelengths. Absorption bands of different natures\nwere assigned in terms of concentration behaviour and\ntemperature dependent photoluminescence. The low-energy structured band was due\nto f -> d transitions within the Eu2+ electronic configuration. The\nproximity of the high-energy d levels to the conduction band induces\nself-ionization of Eu2+. The high-energy absorption bands were assigned to\nself-trapped excitons.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> RARE-EARTH IONS;\nINORGANIC-COMPOUNDS; CRYSTALS; SPECTROSCOPY; EU2+; SPECTRA; LUMINESCENCE;\nEXCITATION; CENTERS <\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/0953-8984\/18\/46\/008 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

New photoluminescence phenomena in milled MnF2<\/sub> at high pressure<\/summary>
\n

Author<\/strong>(s):  Hernandez<\/strong>, I., Rodriguez,\nF.,  Hochheimer,\nH. D.<\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 26    Issue:<\/strong> 4    Pages:<\/strong>\n331-334     <\/p>\n\n\n\n

Abstract:<\/strong> This work presents a time-resolved\nspectroscopic study of MnF2<\/sub> as grown and milled into nanoparticles. We find that high pressure (HP) induces\nphotoluminescence (PL) at room temperature (RT) above 13 GPa in MnF2<\/sub> single crystals. RT-PL occurs\nas a consequence of the inhibition of excitation migration processes among Mn2+\nions resulting from the HP-induced structural phase transition (SPT) to the\nalpha-PbCl2-type phase. This SPT involves important changes in the Mn-F-Mn exchange paths yielding radiative\nde-excitation in Mn2+, and thus also PL. As a salient result, we have found an\nincrease of the PL-quenching temperature in nanosized\nmilled MnF2<\/sub>.<\/p>\n\n\n\n

Author Keywords:<\/strong> photoluminescence; high pressure; nanoparticles; MnF2<\/sub>; time-resolved spectroscopy;\nphase transition <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/089579506001104096<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced luminescence from broadband to narrow-line emission in Cr3+<\/sup>-doped LiCaAlF6<\/sub> at room temperature<\/summary>
\n

Author<\/strong>(s): <\/strong>Sanz-Ortiz, M. N., Rodriguez, E., Hernandez, I.,\nValiente, R., Kuecks, S. <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 26    Issue:<\/strong> 4    Pages:<\/strong>\n345-348     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates pressure-induced\nexcited-state-crossover phenomena in Cr3+-doped LiCaAlF6 at room temperature.\nThe aim is to find the structural requirements yielding the change in the Cr3+\nphotoluminescence (PL) behaviour from a single\nbroadband emission, which is located at 1.62eV (765 nm) at ambient conditions,\nto a ruby-like narrow-line emission at 1.87 eV (662\nnm). For this purpose, emission and excitation spectroscopy as well as lifetime\nmeasurements as a function of pressure were performed in the 0-35 GPa range. Interestingly, we have\nbeen able to transform the broadband Cr3+\n PL at ambient pressure into a ruby-like emission\nat 28 GPa. This behaviour, together with the variations of the E-2 and\nT-4(2) excited-state energies, and the PL lifetime with pressure, can be\nexplained on the basis of the electron-ion coupling associated with the T-4(2)\nand E-2 states.<\/p>\n\n\n\n

Author Keywords:<\/strong> Spectroscopy; high pressure;\nphotoluminescence; Cr3+; excited-state crossover<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> SPECTROSCOPY <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950601104237 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2005<\/strong><\/p>\n\n\n\n

Yb3+<\/sup>-sensitized visible Ni2+<\/sup> photon upconversion in codoped CsCdBr3<\/sub> and CsMgBr3<\/sub><\/summary>
\n

Author(s):<\/strong> Garcia-Revilla\nS, Gerner P, Gudel HU<\/a>, Valiente R <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 72    Issue:<\/strong> 12  Article<\/strong> Number:<\/strong>\n125111     <\/p>\n\n\n\n

Abstract:<\/strong> Near-infrared excitation of Yb3+\nF-2(7\/2)->F-2(5\/2) at 10\n 600 cm(-1) in the linear chain CsMBr3:Ni2+,Yb3+ (M=Cd,Mg) structure leads to green luminescence from Yb3+\npairs and red Ni2+ upconversion luminescence at\ncryogenic temperatures. The broad red upconversion\nluminescence is assigned to the T-1(2g)->(3)A(2g) transition\nof Ni2+. The upconversion excitation spectrum\nindicates that the active mechanism in these systems involves both Yb3+ and\nNi2+ ions. Lifetime and power dependence data allow one to identify a\nground-state-absorption (GSA) energy-transfer upconversion\n(ETU) as the underlying upconversion mechanism for\nthe Yb3+-Ni2+ system in doubly doped CsCdBr3 and CsMgBr3. A less efficient\nsingle-ion GSA excited-state-absorption (ESA) process within Ni2+ is also\nobserved in the title compounds. However, whereas the GSA\/ESA process requires\nan excitation energy above 11\n 200 cm(-1),\nit is possible to sensitize the Ni2+ upconversion via\nYb3+ excitation at energies around 10 200 cm(-1) and around 10 600 cm(-1) in CsCdBr3\nand CsMgBr3. It is shown that only those Ni2+ ions neighboring to Yb3+ ions are\nrelevant for the upconversion induced by Yb3+\nexcitation.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> HIGHER-EXCITED-STATE; YB3+ DOPED CSMNCL3; CR3+ E-2 EMISSION; TRANSITION-METAL; LUMINESCENCE PROPERTIES; CHLORIDE LATTICES; NEAR-IR; NONRADIATIVE PROCESSES; EXCITATION AVALANCHE; COUPLED PAIRS Visible Ni2+<\/sup> upconversion luminescence in Ni2+<\/sup>, Yb3+<\/sup> co-doped CsCdBr3<\/sub>KeyWords Plus:<\/strong> HIGHER-EXCITED-STATE; YB3+ DOPED CSMNCL3; CR3+ E-2 EMISSION; TRANSITION-METAL; LUMINESCENCE PROPERTIES; CHLORIDE LATTICES; NEAR-IR; NONRADIATIVE PROCESSES; EXCITATION AVALANCHE; COUPLED PAIRS <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.72.125111 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Visible Ni2+<\/sup> upconversion luminescence in Ni2+<\/sup>, Yb3+<\/sup> co-doped CsCdBr3<\/sub><\/summary>
\n

Author(s):<\/strong> Garcia-Revilla S, Gerner P, Wenger OS, Gudel HU, Valiente R <\/p>\n\n\n\n

Source:<\/strong> CHEMICAL PHYSICS LETTERS    Volume:<\/strong> 401    Issue:<\/strong> 4-6    Pages:<\/strong>\n492-496     <\/p>\n\n\n\n

Abstract:<\/strong> Excitation around 10200 and 10600 cm(-1) into the\nabsorption peaks of Yb (3+) leads to visible Ni2+\nT-1(2g)–>(3)A(2g) upconversion luminescence in\nthe doubly doped CSCdBr3: Ni2+, Yb (3+) at cryogenic\ntemperatures. The excitation spectrum indicates that ail i2l 3Yb(3+)\nabsorption step is involved in the upconversion\nprocess leading to visible Ni2+ luminescence. This process via Yb3+ excitation\nis more efficient than the upconversion mechanism involving\nonly Ni2+, which is observed in the title compound for excitation energies\nabove 11200 cm(-1).\nUpconversion lifetimes point towards an energy\ntransfer upconversion mechanism for the Ni2+\/Yb3+\nsystem in CsCdBr3 (C) 2004 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CR3+ E-2 EMISSION; TRANSITION-METAL;\nNEAR-IR; LATTICES; GREEN; MN2+; EXCITATION; HALIDES; CSMNCL3 <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.cplett.2004.11.115\n<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2004<\/strong><\/p>\n\n\n\n

Pressure-induced Jahn-Teller suppression in Rb2<\/sub>CuCl4<\/sub>(H2<\/sub>O)(2): Pseudo-Jahn-Teller effect<\/summary>
\n

Author(s):<\/strong> Aguado F, Rodriguez F, Valiente R, Itie JP, Munsch P
<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 70    Issue:<\/strong> 21  Article<\/strong> Number:<\/strong>\n214104     <\/p>\n\n\n\n

Abstract:<\/strong> In this work we investigate the variation of\nthe local structure around Cu2+ as well as the crystal structure in Rb2CuCl4(H2O)(2) through x-ray absorption spectroscopy (XAS)\nand x-ray diffraction (XRD) as a function of pressure. We show that the\napplication of pressure induces a local structural change in the Jahn-Teller (JT) CuCl4(H2O)(2)(2-) complex from an axially\nelongated complex to a compressed one, yielding disappearance of the JT\ndistortion related to the four in-plane Cl- ligands, which are responsible for the antiferrodistortive\nstructure displayed by the crystal at ambient pressure. According to the\nPseudo-Jahn-Teller (PJT) theory (electron-phonon\ncoupling Ecircle timese),\nthe presence of water ligands enhances the JT release\nat pressures well below the metallization pressure. The results are compared\nwith recent pressure experiments on A(2)CuCl(4) layered perovskites and heteronuclear CuCl4L2 complex series, L :Cl–>H2O–>NH3, and explained on the basis of the PJT\nmodel.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> PARAMAGNETIC-RES SPECTRA; OPTICAL-PROPERTIES;\nSTRUCTURAL CORRELATIONS; TEMPERATURE-DEPENDENCE; COMPRESSED OCTAHEDRA;\nCHARGE-TRANSFER; EPR-SPECTRUM; CRYSTAL; LAYER; STATE <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.70.214104<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Three-dimensional magnetic ordering in the Rb2<\/sub>CuCl4<\/sub> layer perovskite – structural correlations<\/summary>
\n

Author<\/strong>(s):<\/strong> Aguado F, Rodriguez F, Valiente R, Senas A, Goncharenko I <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n16    Issue:<\/strong>\n12    Pages:<\/strong>\n1927-1938     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the magnetic structure\nof Rb2CuCl4 as a function of pressure and temperature using neutron\ndiffraction. As in most A(2)CuCl(4)\nlayered perovskites, there is a 2D ferromagnetic\norder within the layers. This behaviour is due to the\nJahn-Teller (JT) antiferrodistortive\nstructure of the CuCl6 units. Rb2CuCl4 undergoes a 3D magnetic transition at\nT-N = 16 K, which mainly depends on the weak antiferromagnetic\ninterlayer interaction. The pressure slightly increases T-N, as partial derivativeT(N)\/partial\nderivativeP = 0.13 K kbar(-1).\nThis behaviour is interpreted in terms of\npressure-induced tilts and reduction of interlayer distance, both effects\nincreasing the anti ferromagnetic exchange coupling between layers. The results\nare compared with previous magnetic studies under chemical and hydrostatic\npressure along layered perovskites series of\n[CnH2n+1NH3](2)CuCl4 (n = 1-3) and BMnF4 (B = Li, Na,\nK, Rb, Tl, Cs and NH4)\ninvolving JT ions of Cu2+ and Mn3+, respectively. We show that the ratio of the\ninterlayer to intralayer coupling, and thus the\nnature of the magnetic order, can be tuned by chemical or hydrostatic pressure\nalong the A(2)CuCl(4)\nseries. The present findings stress the relevance of octahedral tilts on the\nmagnetic behaviour of layered perovskites.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> 2-DIMENSIONAL HEISENBERG-FERROMAGNET;\nNEUTRON-SCATTERING MEASUREMENTS; ELECTRON-PARAMAGNETIC-RES; CRYSTAL-STRUCTURE;\nSUPEREXCHANGE INTERACTION; HYDROSTATIC-PRESSURE; PLANAR FERROMAGNET;\nSUSCEPTIBILITY; K2CUF4; EXCHANGE <\/p>\n\n\n\n

DOI:<\/strong> 10.1088\/0953-8984\/16\/12\/003<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Near-infrared to green photon upconversion in Mn2+<\/sup> and Yb3+<\/sup> doped lattice<\/summary>
\n

Author<\/strong>(s):<\/strong> Reinhard C, Gerner P, Rodriguez F, Garcia-Revilla S, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> CHEMICAL PHYSICS\nLETTERS    Volume:<\/strong>\n386    Issue:<\/strong>\n1-3    Pages:<\/strong>\n132-136     <\/p>\n\n\n\n

Abstract:<\/strong> Yb3+ excitation in the near-infrared around 1\nmum leads to green Mn2+.4T1 –>(6)A(1) luminescence in CaZnF4:Mn2+; Yb3+, ZwSiO(4):Mn2+; Yb3+ and SrZnCl4:Mn2+; Yb3+ at 15 K. In the\nformer two compounds the green upconversion (UC)\nluminescence is visible by eye up to room temperature. In Cs3MnBr5:Mn2+; Yb3+\nno UC luminescence is observed. The UC mechanism\nconsists of a sequence of ground-state absorption and excited-state absorption\nsteps. The UC efficiency at 15 K is of the order of 1% for laser excitation\nwith 130 mW (f = 53 mm focusing lens). (C)\n2004 Elsevier B.V. All rights reserved.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> CRYSTAL-STRUCTURES; LUMINESCENCE;\nCSMNCL3 <\/p>\n\n\n\n

DOI:<\/strong> 10.1016\/j.cplett.2003.12.127 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Correlation between the structure and optical properties of perovskites at high pressure<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF <\/p>\n\n\n\n

Source:<\/strong> HIGH-PRESSURE CRYSTALLOGRAPHY   Book Series:<\/strong> NATO SCIENCE\nSERIES, SERIES II: MATHEMATICS, PHYSICS AND CHEMISTRY    Volume:<\/strong> 140    Pages:<\/strong>\n341-352     <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHARGE-TRANSFER; HYDROSTATIC-PRESSURE; CRYSTAL;\nSPECTRUM; SPECTROSCOPY; IMPURITIES; DEPENDENCE; DISTORTION; COMPLEXES; LATTICE <\/p>\n\n\n\n

Reprint Address:<\/strong> Rodriguez, F (reprint author), Univ Cantabria, Fac Ciencias, DCITIMAC, E-39005\nSantander, Spain <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2003<\/strong><\/p>\n\n\n\n

Pressure effects on NaMnF4<\/sub>: Structural correlations and Jahn-Teller effect from crystal-field spectroscopy<\/summary>
\n

uthor<\/strong>(s):<\/strong> Aguado F, Rodriguez F, Nunez P <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 67    Issue:<\/strong> 20  Article<\/strong> Number:<\/strong> 205101<\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the optical absorption\nspectrum of the NaMnF4-layered perovskite and its\nvariation with pressure. The spectrum basically consists of three broadbands located at 1.916, 2.263, and 2.817 eV, which correspond to the crystal-field (CF) transitions\nB-5(1g)–>(5)Gamma(i) (Gamma(i)=A(1g),\nB-2g, and E-g) with the Jahn-Teller- (JT-) distorted\nMnF63- complex (Mn3+ d(4) configuration). In addition, there are two spin-flip\nB-5(1g)–>B-3(1g) peaks at 2.397 and 2.890 eV, which are activated by the exchange mechanism. Their\nvariation with pressure reveals that the JT energy does not change\nsignificantly with pressure: partial derivativeE(JT)\/partial derivativeP=0.8 meV\/GPa. Furthermore, the variation of the JT tetragonal\nsplitting of the parent octahedral e(g) and t(2g), termed Delta(e) and\nDelta(t), respectively, clearly indicate that partial derivativeDelta(e)\/partial\nderivativeP<&PARTIAL;&UDelta;(t)\/&PARTIAL;P,\nalthough &UDelta;(e)&AP;4&UDelta;(t). The\nCF energies and their pressure shift are explained in terms of local structural\nchanges within the MnF63- complex induced by pressure. The structural\ncorrelation analysis reveals that the reduction of the MnF63- JT distortion is\nsmaller than the expected one on the basis of the crystal volume reduction,\nthus indicating tilt phenomena. This interpretation is supported by the\ndecrease of in-layer Mn-F-Mn superexchange,\nsuch as is derived from the optical spectra. We demonstrate that the equatorial\nand axial distances decrease from 1.839 to 1.808 Angstrom and from 2.167 to\n2.107 Angstrom, respectively, in the 0-10 GPa\nrange.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> METAL-LIGAND DISTANCE; MAGNETIC-STRUCTURES;\nFERROMAGNET CSMNF4; OPTICAL-SPECTRUM; SINGLE-CRYSTAL; DEPENDENCE; PEROVSKITES;\nTRANSITION; FLUORIDES; 10DQ <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.67.205101 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced closure of the Jahn-Teller distortion in Rb2<\/sub>CuCl4<\/sub>(H2<\/sub>O)2<\/sub><\/summary>
\n

Author<\/strong>(s):<\/strong> Aguado F, Rodriguez F, Valiente R, Itite JP, Munsch P <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 23    Issue:<\/strong> 1-2    Pages:<\/strong>\n181-186     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the pressure-induced\nvariation of the local structure around Cu2+ as well as the crystal structure\nin Rb2<\/sub>CuCl4<\/sub>(H2<\/sub>O)(2)\nthrough XAS and XRD techniques. The application of pressure induces a\nstructural change in the Jahn-Teller (JT) CuCl4(H2O)(2)(2-) mplex from\naxially elongated to compressed. This change leads to the closing of the 2D JT\ndistortion related to the four in-plane Cl- ligands, which are responsible for the antiferrodistortive\nstructure displayed by the crystal. It is shown that the presence of water ligands enhances a JT release. Their associated axial ligand-field favours the\noccurrence of such a local structural transition below the metallization\npressure. The results are compared with recent pressure experiments on A(2)CuCl(4) systems.<\/p>\n\n\n\n

Author Keywords:<\/strong> Cu2+<\/sup>; CuCl4<\/sub>(H2<\/sub>O)(2);\nJahn-Teller effect; XRD and XAS under pressure; layer\nperovskite <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHARGE-TRANSFER; CRYSTAL; NH4CL;\nXANES; EDGE; CU <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/0895795031000147731<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Experiments with a sunbird<\/summary>
\n

uthor(s):<\/strong> Guemez J, Valiente R, Fiolhais C, Fiolhais M <\/p>\n\n\n\n

Source:<\/strong>\nAMERICAN JOURNAL OF PHYSICS    Volume:<\/strong> 71    Issue:<\/strong> 12    Pages:<\/strong>\n1264-1267     <\/p>\n\n\n\n

Abstract:<\/strong> A\ntheoretical description of the sunbird, a drinking bird without any external\nliquid, is compared with experiment. The transient times and the periods of\noscillation given by a simulation of the dynamics agree with the measured\nvalues. (C) 2003 American Association of Physics Teachers.<\/p>\n\n\n\n

Reprint Address:<\/strong>\nGuemez, J (reprint author), Univ Cantabria, Dept Fis Aplicada, E-39005\nSantander, Spain <\/p>\n\n\n\n

DOI:<\/strong> 10.1119\/1.1603273 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Intrinsic and extrinsic photoluminescence in the NH4<\/sub>MnCl3<\/sub> cubic perovskite: a spectroscopic study<\/summary>
\n

Author(s):<\/strong> Hernandez\nI, Rodriguez F <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n15    Issue:<\/strong>\n13    Pages:<\/strong>\n2183-2195     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the photoluminescence\n(PL) properties of the cubic chloroperovskite\nNH4MnCl3. Like in most concentrated materials, the Mn2+ PL which is located at 2.10 eV at T = 10 K strongly depends on the temperature. Optical\nabsorption (OA), emission, and excitation spectroscopy, as well as lifetime\nmeasurements, performed on NH4MnCl3 indicate that the PL is mainly intrinsic at\nT = 10 K and consists of a broad band located at 2.10 eV.\nAbove this temperature, the PL gradually transforms to extrinsic PL due to exciton migration and subsequent trapping. Further\ntemperature increase above 100 K yields transfer to killers of excitation which\nare responsible for the PL quenching, and hence the absence of PL at ambient\nconditions. The exciton traps are identified with\nperturbed Mn2+ sites with the effective activation energy of 52 meV, whilst the activation energy for energy transfer is 47\nmeV. The existence of these traps has been directly\nrevealed by time-resolved spectroscopy. The detected intrinsic and extrinsic PL\nbands are displaced by 6 meV, which coincides with\nthe activation energy difference between pure Mn2+ and trap Mn2+, as derived\nfrom temperature dependence studies of the lifetime T(T).\nInterestingly, a PL band at 1.82 eV is observed above\n60 K. This band, which was initially associated with deeper excitation traps,\nactually corresponds to precipitates of MnCl2 inside NH4MnCl3. The correlation\nanalysis performed on NH4MnCl3 using OA, PL, and lifetime data provides an\nestimate of the precipitate concentration of 0.3 mol %. The presence of two\nseparated Mn2+ PL bands at different temperatures is a rather common phenomenon\nin concentrated materials such as AMnX(3) (A = NH4, Rb; X = Cl, F), and has been\ninterpreted in terms of exciton transfer to deeper\ntraps. The present finding stresses the relevance of an adequate structural\ncharacterization in dealing with PL in concentrated materials.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> OPTICAL-SPECTRUM; ENERGY-TRANSFER;\nCRYSTALS; TRANSITIONS; DEPENDENCE; DISTANCE; LUMINESCENCE; ABSORPTION;\nEXCITATION; DYNAMICS <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Multiphonon radiationless phenomena in Mn2+<\/sup>-doped Ca1-xSrxF2<\/sub> and BaF2<\/sub> fluorites<\/summary>
\n

Author(s):<\/strong> Hernandez\nI, Rodriguez F <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 23    Issue:<\/strong> 1-2    Pages:<\/strong> 155-160<\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the surprising\ndisappearance of the Mn2+ photoluminescence on passing from CaF2:Mn2+ to\nSrF2:Mn2+ or BaF2:Mn2+ using pressure spectroscopy. We show that the loss of\nluminescence in these systems is associated with non-radiative\nthermally activated processes whose activation energy and pre-exponential rates\nstrongly depend on the crystal volume irrespective of the chemical composition.\nA salient feature is the PL enhancement observed in the cotunnite\nhigh-pressure phase along the series. This enhancement is explained in terms of\nthe large volume reduction at the phase transition, as well as by the presence\nof low-symmetry crystal fields attained at the cation\nsites leading to an increase of the radiative\ntransition rate by the electric-dipole mechanism.<\/p>\n\n\n\n

Author Keywords:<\/strong> high-pressure spectroscopy;\nphotoluminescence; radiationless process; Mn2+-doped\nfluorites; fluorite-cotunnite phase transition <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> MN2+ IONS; PRESSURE; PHOTOLUMINESCENCE; ENHANCEMENT <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/0895795031000147777 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Correlations between structure and optical properties in Jahn-Teller Mn3+<\/sup> fluorides: A study of TlMnF4<\/sub> and NaMnF4<\/sub> under pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> Rodriguez F, Aguado F <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL\nPHYSICS    Volume:<\/strong>\n118    Issue:<\/strong>\n24    Pages:<\/strong>\n10867-10875  <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the Jahn-Teller\n(JT) distortion in different Mn3+ fluoride series by optical absorption (OA)\nspectroscopy. The aim is to establish correlations between the local structure\nof the formed MnF63- derived from x-ray diffraction and the JT splitting\nassociated with the parent octahedral E-5(g)(3z(2)-r(2),x(2)-y(2)) and T-5(2g)(xy,xz,yz) states, Delta(e) and Delta(t), obtained from the\nOA spectrum. A salient feature is the linear relation exhibited by both Delta(e) and Delta(t) with the tetragonal coordinate\nQ(theta) along the whole series. From these relations we derive suitable\nelectron-ion coupling coefficients related to the E-5(g) and T-5(2g) states\nwhose values play a key role in the exE and exT JT theory, respectively. The results of these\ncorrelations are applied to investigate the structural variations undergone by\nthe two-dimensional compounds NaMnF4 and TlMnF4 under pressure using OA\nspectroscopy. Interestingly, the analysis carried out is relevant since it\nprovides useful information on the Mn3+ local structure, a task that is\ndifficult to achieve using extended x-ray-absorption fine structure under\npressure due to the high absorption of the diamond anvils. We conclude that the\neffect of pressure in NaMnF4 is to reduce progressively the JT distortion of\nthe complex, keeping its tetragonal symmetry. The pressure effects in TlMnF4\nare more drastic, leading to pressure-induced structural phase transitions of\nlow symmetry. At variance with NaMnF4, the high-pressure Mn3+ local structure\nseems to have significant rhombic distortions. (C) 2003 American Institute of\nPhysics.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> MAGNETIC-STRUCTURES;\nCRYSTAL-STRUCTURE; FERROMAGNET CSMNF4; TRANSITION; SPECTRUM; FIELD;\nFLUOROMANGANATES(III); PEROVSKITES; DISTORTION; ABSORPTION <\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.1569847 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence and radiationless processes in Mn2+<\/sup>-doped Ca1-xSrxF2<\/sub> fluorites as a function of pressure and temperature. A structural correlation study<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF, Hernandez I, Moreno M, Alcala R <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL\nPHYSICS    Volume:<\/strong>\n119    Issue:<\/strong>\n16    Pages:<\/strong>\n8686-8694   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the photoluminescence\n(PL) properties of Mn2+-doped fluorites in CaF2, BaF2, SrF2, and in solid\nsolutions Ca1-xSrxF2. In particular, we focus on the radiationless\nprocesses leading to the surprising disappearance of the Mn2+ PL on passing from CaF2: Mn2+ to\nSrF2: Mn2+ or BaF2: Mn2+. For this purpose emission, excitation, lifetime, and\ntime-resolved spectroscopy as a function of pressure and temperature are\ncarried out in these compounds as well as in the Ca1-xSrxF2:Mn2+ (x=0-1) series\nusing pressure spectroscopy. We show that the quenching of PL in these systems\nis associated with nonradiative thermal activated\nprocesses whose activation energy and pre-exponential rates strongly depend on\nthe crystal volume irrespective of the chemical composition of the host\ncrystal. A salient feature of this work deals with the increase of activation\nenergy induced by pressure, whose variation with the lattice parameter is given\nby E-a(eV)=1.02-2.64\n(a-5.46), with a(CaF2)=5.46 Angstrom. It leads to a PL quantum yield\nenhancement, which favors appearance of Mn2+ PL even in the non-PL systems\nSrF2:Mn2+ and BaF2:Mn2+. Furthermore, the activation energy mainly depends on\nthe crystal volume per molecule irrespective of the crystal structure or the\nlocal symmetry around the impurity. In this way, the relevance of the\nfluorite-to-cotunnite phase transition to enhance PL\nis analyzed. This enhancement is explained in terms of the large volume\nreduction at the phase transition, as well as by the presence of low-symmetry\ncrystal fields attained at the cation site yielding\nan increase of the radiative transition rate by the\nelectric-dipole mechanism.(C) 2003 American Institute\nof Physics.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> MN2+<\/sup> IONS; CRYSTALS; BAF2<\/sub>;\nLUMINESCENCE; INSTABILITY; ENHANCEMENT; TRANSITIONS; SUPPRESSION; DEPENDENCE;\nDISTANCE <\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.1611874 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Cooperative Yb3+<\/sup>-Tb3+<\/sup> dimer excitations and upconversion in Cs3<\/sub>Tb2<\/sub>Br9<\/sub> : Yb3+<\/sup><\/summary>
\n

Author(s):<\/strong> Salley GM, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 67    Issue:<\/strong> 13  Article<\/strong> Number:<\/strong>\n134111    <\/p>\n\n\n\n

Abstract:<\/strong> Green Tb3+ D-5(4)–>F-7(J)\nluminescence visible by eye is observed under near-infrared laser excitation.\nOptical spectroscopic techniques including absorption, luminescence, and\nexcitation spectroscopy are used to characterize this upconversion\n(UC) luminescence. The Tb3+ UC luminescence is present for all temperatures\nwithin a range from 10 to 300 K, and gains intensity by three orders of\nmagnitude between 10 and 300 K. For Tgreater than or\nequal to100 K the dominant upconversion mechanism is\nthe cooperative sensitization of Tb3+ by two Yb3+ ions. In this temperature\nregime the Tb3+ UC luminescence dominates the visible (VIS)\nspectrum for all near-infrared (NIR) excitations, resulting in the\ncharacteristic green luminescence. At 10 K, the color of the luminescence\nchanges from green to blue, depending on the excitation wavelength\ncorresponding to the dominance of Tb3+ UC luminescence or the Yb3+-Yb3+\ncooperative pair luminescence. Two color excitation\nspectroscopy is performed to directly observe an excited state\nabsorption (ESA) step in the Tb3+ UC luminescence excitation spectrum at 10 K.\nThis allows the unambiguous assignment of a type of ground state\nabsorption\/excited state absorption (GSA\/ESA) mechanism responsible for the upconversion in this system at 10 K. We explain this\ncooperative interaction in the framework of an Yb3+-Tb3+ exchange-coupled dimer. An energy level diagram for this dimer\nis presented. Excitation into dimer levels around\n12000-14500 cm(-1),\nwhere neither Yb3+ nor Tb3+ single ions have levels, leads to Yb3+ luminescence\nat 10 K. For laser excitation, 53 W\/mm(2), resonant\nwith an ESA transition a VIS\/NIR photon ratio of 2.7(10)(-5) is found at 10 K.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> LUMINESCENCE UP-CONVERSION; YB3+ DOPED CSMNCL3;\nEXCHANGE INTERACTIONS; NEUTRON SPECTROSCOPY; TRANSITION-METAL; ENERGY-TRANSFER;\nNEAR-IR; CS3YB2BR9; SYSTEMS; MECHANISMS <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.67.134111 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure-induced photoluminescence in Mn2+-doped BaF2 and SrF2 fluorites<\/summary>
\n

Author<\/strong>(s):<\/strong> Hernandez,\nI., Rodriguez, F<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 67    Issue:<\/strong> 1  Article<\/strong> Number:<\/strong>\n012101     <\/strong><\/p>\n\n\n\n

Abstract:<\/strong> This work reports an effective way for inducing\nroom temperature photoluminescence (PL) in Mn2+-doped BaF2 and SrF2 using\nhigh-pressure techniques. The aim is to understand the surprising PL behavior\nexhibited by Mn2+ at the cubal site of the fluorite\nstructure. While Mn2+-doped CaF2 shows a green PL with quantum yield close to 1\nat room temperature, Mn2+-doped MF2 (M=Ba,Sr) is not\nPL either at room temperature (SrF2) or at any temperature (BaF2) at ambient\npressure. We associate the loss of Mn2+\n PL on passing from CaF2 to SrF2 or BaF2 with nonradiative multiphonon\nrelaxation whose thermal activation energy decreases along the series\nCaF2–>SrF2–>BaF2. A salient feature of this work deals with the\nincrease of activation energy induced by pressure. It leads to a quantum yield\nenhancement, which favors PL recovery. Furthermore, the activation energy\nmainly depends on the crystal volume per molecule irrespective of the crystal\nstructure or the local symmetry around the impurity. In this way, the relevance\nof the fluorite-to-cotunnite phase transition is\nanalyzed in connection with the PL properties of the investigated compounds.\nThe PL spectrum and the corresponding lifetime are reported for both structural\nphases as a function of pressure.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> MN2+ IONS; CRYSTALS; LUMINESCENCE; INSTABILITY;\nTRANSITIONS; DEPENDENCE; DISTANCE <\/p>\n\n\n\n

Reprint Address:<\/strong> Rodriguez, F\n(reprint author), Univ\nCantabria, Fac Ciencias, Dept\nCiencias Tierra & Fis\nMat Condensada, E-39005 Santander, Spain <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.67.012101 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2002<\/strong><\/p>\n\n\n\n

Optical spectroscopy of Al2<\/sub>O3<\/sub> : Ti3+ <\/sup>single crystal under hydrostatic pressure. The influence on the Jahn-Teller coupling<\/summary>
\n

Author(s):<\/strong> Garcia-Revilla\nS, Rodriguez F, Valiente R, Pollnau M <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n14    Issue:<\/strong>\n3    Pages:<\/strong>\n447-460     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the effect of\nhydrostatic pressure on the excitation and emission spectra, as well as on the\nlifetime, of Al2O3:Ti3+ at room temperature. The aim is to establish\ncorrelations between the pressure-induced band shifts and the corresponding\nlocal structural changes undergone by the TiO6 complex. A blue-shift of 8.52\nand 6.86 cm(-1) kbar(-1) was found for the\nlower (E-1) and upper (E-2) energy components of the excitation band at 17 760\nand 20500 cm(-1),\nrespectively, and blue-shifts of 5.93 and 5.40 cm(-1) kbar(-1) for the two overlapping bands of the emission\nspectrum located at 12 680 and 14210\n cm(-1). We explain these results on the basis of a\nreduction of the TiO6 Jahn-Teller distortion upon\nincreasing the pressure, In contrast, the increase of the overall Stokes shift,\nwhich is mainly associated with electron-vibration coupling to the totally\nsymmetric a(1g) vibration, is explained by the increase of the excited-state\nstabilization energy, S(a1g)homega(a1g), with increasing\npressure. <\/p>\n\n\n\n

The luminescence lifetime is also found to be pressure\ndependent, varying from 2.6 mus at ambient conditions\nto 3.2 mus at 80 kbar. This\nincrease is caused by a diminution of the transition oscillator strength that\nis related to the odd-vibration assistance mechanism. The softening of the\ntransition mechanism is interpreted in terms of the blue-shift experienced by\nthe O2- –> Ti3+ charge-transfer transition energy upon increasing the\npressure.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHROMIUM PHOTOLUMINESCENCE; LOCAL\nCOMPRESSIBILITIES; STOKES SHIFT; DEPENDENCE; TRANSITIONS; ABSORPTION;\nELPASOLITES; SAPPHIRE; DISTANCE; SPECTRA <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Pressure effects on the cooperative Jahn-Teller distortion in AMnF4<\/sub> (A=Na, Tl)<\/summary>
\n

Author<\/strong>(s):<\/strong> Aguado F, Rodriguez F, Nunez P <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 22    Issue:<\/strong> 1    Special Issue:<\/strong> Sp. Iss. SI    Pages:<\/strong> 121-126     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the Optical Absorption\nspectrum of the AMnF(4) layer perovskites of Mn3+, and\nits variation with the pressure. We show that the crystal-field transition\nenergies and their pressure shifts provide a very\nuseful information about the local structural changes in the MnF63- complex and\nhow it changes with the pressure, once the correlations between crystal-field\nelectronic structure and coordination geometry around Mn3+ has been\nestablished. Along this work we demonstrate that the equatorial and axial\ndistances decrease from 1.844 to 1.813 Angstrom, and\nfrom 2.167 to 2.090 Angstrom, respectively, in the 0-100 kbar\nrange, leading to a partial reduction of the Jahn-Teller\ndistortion.<\/p>\n\n\n\n

Author Keywords:<\/strong> Mn3+; MnF63-; Jahn-Teller\neffect; pressure spectroscopy; layer perovskite <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CRYSTAL <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950290003094<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical spectroscopy of Al2<\/sub>O3<\/sub> : Ti3+ <\/sup>single crystal under hydrostatic pressure. The influence on the Jahn-Teller coupling<\/summary>
\n

Author(s):<\/strong> Garcia-Revilla\nS, Rodriguez F, Valiente R, Pollnau M <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n14    Issue:<\/strong>\n3    Pages:<\/strong>\n447-460     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the effect of\nhydrostatic pressure on the excitation and emission spectra, as well as on the\nlifetime, of Al2O3:Ti3+ at room temperature. The aim is to establish\ncorrelations between the pressure-induced band shifts and the corresponding\nlocal structural changes undergone by the TiO6 complex. A blue-shift of 8.52\nand 6.86 cm(-1) kbar(-1) was found for the\nlower (E-1) and upper (E-2) energy components of the excitation band at 17 760\nand 20500 cm(-1),\nrespectively, and blue-shifts of 5.93 and 5.40 cm(-1) kbar(-1) for the two overlapping bands of the emission\nspectrum located at 12 680 and 14210\n cm(-1). We explain these results on the basis of a\nreduction of the TiO6 Jahn-Teller distortion upon\nincreasing the pressure, In contrast, the increase of the overall Stokes shift,\nwhich is mainly associated with electron-vibration coupling to the totally\nsymmetric a(1g) vibration, is explained by the increase of the excited-state\nstabilization energy, S(a1g)homega(a1g), with increasing\npressure. <\/p>\n\n\n\n

The luminescence lifetime is also found to be pressure\ndependent, varying from 2.6 mus at ambient conditions\nto 3.2 mus at 80 kbar. This\nincrease is caused by a diminution of the transition oscillator strength that\nis related to the odd-vibration assistance mechanism. The softening of the\ntransition mechanism is interpreted in terms of the blue-shift experienced by\nthe O2- –> Ti3+ charge-transfer transition energy upon increasing the\npressure.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHROMIUM PHOTOLUMINESCENCE; LOCAL\nCOMPRESSIBILITIES; STOKES SHIFT; DEPENDENCE; TRANSITIONS; ABSORPTION;\nELPASOLITES; SAPPHIRE; DISTANCE; SPECTRA<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Phonon-assisted cooperative sensitization of Tb3+<\/sup> in SrCl2<\/sub> : Yb, Tb<\/summary>
\n

Author(s):<\/strong> Salley GM, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED\nMATTER    Volume:<\/strong>\n14    Issue:<\/strong>\n22    Pages:<\/strong>\n5461-5475     <\/p>\n\n\n\n

Abstract:<\/strong> Excitation into the Yb3+ F-2(5\/2)\nexcited-states leads to visible-by-eye green luminescence spanning the\nspectral. region from 490 to 790 nm, with a quadratic\npower dependence. Optical absorption; luminescence; and excitation spectroscopy\nas well as pulsed measurements on single-crystal SrCl2:Yb(1%),\nTb(1%) are used to determine the upconversion (UC)\nproperties of this system. The upconverted\nluminescence is easily detectable by eye from RT to 100 K, at which point the\nintensity drops significantly and. a change in colour\nfrom green to blue is observed. Pulsed measurements coupled with excitation\nspectroscopy lead to the unambiguous assignment.of a\nphonon assisted cooperative sensitization mechanism as the dominant UC process\nfor T > 50 K with VIS\/NIR photon ratios on the order of 10(-2)% for a laser\npower of 56 W mm(-2). Below 50 K, the-dominant UC emission becomes the\nwell-known Yb-Yb cooperative luminescence:. around 500 nm, with a\nconsequential reduction of Tb3+ emission by more than three orders of magnitude\nfrom RT to 10 K.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> UP-CONVERSION LUMINESCENCE; ENERGY-TRANSFER;\nGLASSES; YTTERBIUM; CRYSTALS; SYSTEMS; RBMNCL3; YB3+<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical spectroscopy of (C2<\/sub>H5<\/sub>NH3<\/sub>)(2)CdCl4<\/sub> : Cu2+<\/sup> under pressure: Study of Cu2+<\/sup> local structure from theoretical calculations<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F, Aramburu JA, Moreno M, Barriuso MT, Sousa C, De Graaf C <\/p>\n\n\n\n

Source:<\/strong> INTERNATIONAL JOURNAL OF QUANTUM\nCHEMISTRY    Volume:<\/strong>\n86    Issue:<\/strong>\n2    Pages:<\/strong>\n239-244     <\/p>\n\n\n\n

Abstract:<\/strong> The variations experienced by the energy\nE-u(pi) of the e(u)(pi) –> b(1g) (similar tox(2)-y(2)) charge-transfer\ntransition of (C2H5NH3)(2)CdCl4:Cu2+ upon pressure in the 0- to 40-kbar range\nhave been measured at room temperature by means of a sapphire anvil cell. These\ndata reveal that E-u(pi) undergoes a red shift of 1400 cm(-1) on passing from\nambient pressure to 40 kbars. To understand this puzzling result theoretical\ncalculations of partial derivativeE(u)(pi)\/partial derivativeR(eq) and partial\nderivativeE(u)(pi)\/partial derivativeR(ax) have been performed where R-eq and\nR-ax mean the equatorial and axial Cu2+-Cl- distances of the elongated CuCl64-\ncomplex, respectively. All results indicate that partial derivativeE(u)(pi)\/partial\nderivativeR(eq) and partial derivativeE(u)(pi)\/partial derivativeR(ax) for R-eq\n= 228 pm and R-ax = 297 pm are indeed negative. Moreover ab initio complete\nactive space self-consistent field (CASSCF\/CASPT2) and density functional\ncalculations lead to partial derivativeE(u)(pi)\/partial\nderivativeR(ax) values, which are about 10 times smaller than those of partial\nderivativeE(u)(pi)\/partial derivativeR(eq). From the ensemble of experimental\nand theoretical results, it is concluded that a pressure of 40 kbars gives rise\nto a decrement of approximate to 25 pm of the axial distance and at the same\ntime to an increase of approximate to 7 pm of the equatorial one. It is\nstressed that the present study on a diluted Jahn-Teller impurity ties far\nbeyond the current possibilities of X-ray absorption structure techniques. (C) 2002 John Wiley & Sons, Inc.<\/p>\n\n\n\n

Author Keywords:<\/strong> CuCl64-; (C2H5NH3)(2)CdCl4\n: Cu2+; high-pressure; optical transitions; DFT calculations; ab initio\ncalculations <\/p>\n\n\n\n

KeyWords Plus:<\/strong> 2ND-ORDER PERTURBATION-THEORY;\nCHARGE-TRANSFER TRANSITIONS; MOLECULAR WAVE-FUNCTIONS; ANO BASIS-SETS;\nHYDROSTATIC-PRESSURE; CRYSTAL-FIELD; DEPENDENCE; APPROXIMATION; EXCITATIONS;\nCOMPLEXES<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Is it possible to use charge transfer bands to measure impurity-ligand distances? Experimental and theoretical results on Cu2+<\/sup> doped (C2<\/sub>H5<\/sub>NH3<\/sub>)(2)CdCl4<\/sub>Upconversion luminescence in Yb3+<\/sup> doped CsMnCl3<\/sub>: Spectroscopy, dynamics, and mechanisms<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F, Barruso MT, Sousa C, de Graaf C, Aramburu JA, Moreno M <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 22    Issue:<\/strong> 2    Special Issue:<\/strong> Sp. Iss. SI    Pages:<\/strong> 475-478     <\/p>\n\n\n\n

Abstract:<\/strong> The present work is focused on the effects\nproduced by hydrostatic pressure on Cu2+ (<100ppm) doped (C2H5NH3)(2)CdCl4 single crystal. The energy E-u(pi) of the e(u)(pi)\n–> b(1)g(similar tox(2) – y(2)) charge-transfer\ntransition of (C2H5NH3)(2)CdCl4: Cu2+ undergoes a red shift of 1400 cm(-1) on passing from\nambient pressure to 40 kbar. To understand this fact theoretical calculations of the CuCl64- complex\nusing four different methods have been carried out. Based on these\ncalculations, it is concluded that the experimental red shift undergone by E-u(pi) can only be reasonably explained through a decrease of\nsimilar to25 pm in R-ax and an increase of similar to7 pm in R-eq leading to a decrement of the CuCl64- volume. Variations\nof any metal-halide distances down to 0.1 pm can be well detected through the\nshifts of the charge-transfer band energy upon pressure.<\/p>\n\n\n\n

Author Keywords:<\/strong> high pressure; optical\nspectroscopy; copper (II); CuCl64-; charge-transfer bands; Jahn-Teller\neffect <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CRYSTAL-FIELD; TRANSITIONS;\nDEPENDENCE; COMPLEXES <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950290014605 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Upconversion luminescence in Yb3+<\/sup> doped CsMnCl3<\/sub>: Spectroscopy, dynamics, and mechanisms<\/summary>
\n

Author(s):<\/strong> Valiente R, Wenger OS, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL\nPHYSICS    Volume:<\/strong>\n116    Issue:<\/strong>\n12    Pages:<\/strong>\n5196-5204    <\/p>\n\n\n\n

Abstract:<\/strong> Single crystals of CsMnCl3 doped with 0.9% Yb3+\nwere grown from the melt by the Bridgman technique and studied by means of\nvariable temperature optical spectroscopy. At cryogenic temperatures,\nnear-infrared Yb3+-excitation around 1 mum leads to intense Mn2+ upconversion luminescence in the red spectral region. This\nvery efficient upconversion process is possible\nbecause of magnetic Yb3+-Mn2+ exchange interactions, and a new type of upconversion mechanism is found to be active in this\nsystem. The upconversion properties of Yb3+:CsMnCl3\nare compared to those of Yb3+:RbMnCl3 and Yb3+:CsMnBr3. The upconversion\nefficiencies at cryogenic temperatures differ by many orders of magnitude. The\nbridging geometry between Yb3+ and Mn2+ is found to be a key factor for the\nefficiency of the process. The highest efficiency is observed for the title\ncompound, and this is correlated with the most likely linear Yb3+-Cl–Mn2+ arrangement\nin this crystal. At 15 K the dominant upconversion\nmechanism in the title compound involves an energy transfer step. By increasing\nthe temperature to 100 K a new and very efficient mechanism involving a\nsequence of ground state and excited state absorption steps becomes dominant. (C)\n2002 American Institute of Physics.<\/p>\n\n\n\n

KeyWords Plus:<\/strong> VISIBLE UP-CONVERSION; COUPLED\nPAIRS; GD3+ IONS; CSCDBR3; EXCITATION; EPR; CRYSTALS; SPECTRA; RBMNCL3; ENERGY <\/p>\n\n\n\n

DOI:<\/strong> 10.1063\/1.1446430<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Luminescence upconversion under hydrostatic pressure in the 3d-metal systems Ti2+<\/sup>: NaCl and Ni2+<\/sup>: CsCdCl3<\/sub><\/summary>
\n

Author(s):<\/strong> Wenger OS, Salley GM, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 65    Issue:<\/strong> 21  Article<\/strong> Number:<\/strong>\n212108     <\/p>\n\n\n\n

Abstract:<\/strong> We present a study of upconversion\nmaterials and processes under external hydrostatic pressure. The near-infrared\nto visible photon upconversion properties of\nTi2+-doped NaCl and Ni2+-doped CsCdCl3 at 15 K are\nstudied as a function of external hydrostatic pressure. It is found that in\nTi2+:NaCl pressure can be used to switch on an\nefficient upconversion mechanism, which is inactive\nat ambient pressure, leading to an order-of-magnitude enhancement of the\noverall upconversion efficiency of this material. For\nNi2+:CsCdCl3 it is demonstrated that upconversion\nluminescence excitation spectroscopy can be used to study the pressure\ndependence of excited state absorption transitions. The results demonstrate the\nability to tune upconversion properties by altering\nthe local crystal field of active ions, in addition to probing the pressure\ndependence of excited state absorption transitions via upconversion\nspectroscopy.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> UP-CONVERSION PROPERTIES; CHLORIDE HOST\nLATTICES; STATE; DEPENDENCE <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevB.65.212108<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Luminescence upconversion under high pressure in Ni2+<\/sup> doped CsCdCl3<\/sub><\/summary>
\n

Author(s):<\/strong> Wenger OS, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 22    Issue:<\/strong> 1    Special Issue:<\/strong> Sp. Iss. SI    Pages:<\/strong> 57-62     <\/p>\n\n\n\n

Abstract:<\/strong> The near-infrared to visible upconversion properties of Ni2+ doped CsCdCl3 are studied\nas a function of hydrostatic pressure. At 15 K and ambient pressure,\nnear-infrared excitation of Ni2+ around 810nm leads to upconversion\nluminescence centered around 610nm. Due to the increase\nof the ligand field strength with increasing\npressure, the emission band moves to higher energies with a rate of 19 cm(-1)\/kbar,\nand at 46 Bar it is centered around 585nm. Thus the upconversion\nluminescence undergoes a color change from red to yellow in the\nI bar-46kbar pressure range. The 15 K pressure-dependent upconversion excitation spectra reveal a slight red-shift\nof -4cm(-1)\/kbar of the upconversion\nrelevant T-3(2g) –> T-1(2g) excited state absorption (ESA) transition, and\nthis is related to a reduction of the Racah B and C\nparameters, caused by an increasing degree of covalency\nin the Ni2+-Cl- interaction towards higher pressures. Thus, with upconversion luminescence excitation spectroscopy we can\nobtain information about the pressure-dependence of an ESA transition. The\npressure-induced intensity redistributions within this excitation spectrum are\nindicative of an increasing spectral overlap of T-3(2g) –> T-1(2g) ESA with\n(3)A(2g) –> T-3(1g) (F-3) ground state absorption, potentially leading to\nmore efficient upconversion at higher pressures than\nat ambient pressure.<\/p>\n\n\n\n

Author Keywords:<\/strong> high pressure; upconversion;\nluminescence; optical spectroscopy; Ni2+ <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHLORIDE; LATTICES; SPECTROSCOPY <\/p>\n\n\n\n

DOI:<\/strong> 10.1080\/08957950290007207<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2001<\/strong><\/p>\n\n\n\n

Influence of hydrostatic pressure on the Jahn-Teller effect in the T-4(2g) excited state of CrCl6<\/sub>3-<\/sup> doped Cs2<\/sub>NaScCl6<\/sub><\/summary>
\n

Author(s):<\/strong> Wenger OS, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL\nPHYSICS    Volume:<\/strong>\n115    Issue:<\/strong>\n8    Pages:<\/strong>\n3819-3826     <\/p>\n\n\n\n

Abstract:<\/strong> The T-4(2g)–>\n(4)A(2g) luminescence of a 4.1% Cr3+ doped Cs2NaScCl6 crystal is studied as a\nfunction of hydrostatic pressure at room temperature and 15 K. The vibrational fine structure observed in the low-temperature\nvariable pressure emission spectra is analyzed with a two configurational\ncoordinate approach, involving the totally symmetric a(1g)\nand the e(g) Jahn-Teller normal coordinate.\nIncreasing hydrostatic pressure is found to reduce the tetragonal distortion of\nthe CrCl63- unit in the electronic T-4(2g) state resulting from the Jahn-Teller effect. Additionally, pressure impedes\nexpansion along the a(1g) coordinate of the CrCl63- complex upon (4)A(2g)–>\nT-4(2g) photo-excitation, and thus has a greater influence on the T-4(2g)\nexcited state than on the (4)A(2g) ground state. The absolute Cr3+-Cl- average\ndistance reduction upon increasing pressure is estimated using a simple point\ncharge model. (C) 2001 American Institute of Physics.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> NEAR-INFRARED LUMINESCENCE; CHROMIUM PHOTOLUMINESCENCE;\nTEMPERATURE-DEPENDENCE; ABSORPTION-SPECTRA; RUBY; SPECTROSCOPY; K2NAGAF6-CR3+;\nELPASOLITES; CALIBRATION; RELAXATION <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical spectroscopy of the Ni2+<\/sup>-doped layer perovskites Rb2<\/sub>MCl4<\/sub> (M = Cd, Mn): Effects of Ni2+<\/sup>-Mn2+<\/sup> exchange interactions on the Ni2+<\/sup> absorption, luminescence, and upconversion properties<\/summary>
\n

Author(s):<\/strong> Wenger OS, Valiente R, Gudel HU <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 64    Issue:<\/strong> 23  Article<\/strong> Number:<\/strong> <\/p>\n\n\n\n

Abstract:<\/strong> Single crystals of Ni2+-doped Rb2CdCl4 and\nRb2MnCl4 are studied by polarized optical absorption and luminescence\nspectroscopy at 15 K. In Ni2+:Rb2MnCl4, Ni2+-Mn2+ exchange interactions, which\noccur exclusively within the perovskite layers of\nthis material, dramatically affect the absorption, luminescence, and up-conversion\nproperties of Ni2+ for light polarized within the layers (sigma): The Ni2+\n(3)A(2g)–>E-1(g) and (1)A(1g) ground-state-absorption (GSA) transitions are\neach enhanced by about an order of magnitude when compared to Ni2+:Rb2CdCl4.\nSimilarly, in Ni2+:Rb2MnCl4 the T-3(2g)–>T-1(2g) excited-state absorption\n(ESA) as well as its reverse luminescence transition experience an intensity\nenhancement in their electronic origin region in sigma polarization. One- and\ntwo-color up-conversion-excitation experiments show that, due to the in-plane\nexchange enhancement of the up-conversion-relevant GSA and ESA transitions in\nNi2+Rb2MnCl4, the near-infrared(NIR) to-visible (VIS) up-conversion process at\n15 K in this material is up to a factor of 55 more efficient for sigma than for\npi -polarized excitation, and also one to two orders of magnitude more\nefficient than in Ni2+:Rb2CdCl4 at the same temperature. The structural\nconditions for efficient Ni2+-Mn2+ exchange interactions are discussed. The\nNIR-to-VIS up-conversion efficiency can be further enhanced by an\nenergy-transfer step from Ni2+ T-1(2g) to Mn2+ T-4(1g),\nhowever, this occurs very inefficiently in Ni2+:Rb2MnCl4.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> EXCITED-STATE LUMINESCENCE; CHLORIDE HOST\nLATTICES; SUPEREXCHANGE INTERACTION; NONRADIATIVE PROCESSES; ELECTRONIC\nEXCITATION; NICKEL IONS; MANGANESE; DYNAMICS; SPECTRA; COMPLEXES <\/p>\n\n\n\n

DOI:<\/strong> 10.1103\/PhysRevLett.64.235116<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Photoluminescence enhancement of Ca1-xSrxF2<\/sub> : Mn2+<\/sup> under pressure<\/summary>
\n

Author<\/strong>(s):<\/strong> Gutierrez RE, Rodriguez F, Moreno M, Alcala R <\/p>\n\n\n\n

Source:<\/strong> RADIATION EFFECTS AND DEFECTS IN\nSOLIDS    Volume:<\/strong>\n154    Issue<\/strong>:<\/strong>\n3-4    Pages:<\/strong>\n287-293    Published:<\/strong>\n2001   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the surprising\ndisappearance of the Mn2+ green photoluminescence (PL) observed at room\ntemperature on passing from CaF2 to SrF2 along the Ca1 – xSrx:Mn2+\nfluorite series. The aim is to understand the microscopic origin of the\nexcited-state relaxation phenomena leading to radiationless\nprocesses in these crystals. High-pressure experiments performed on Ca0.25Sr0.75F2:Mn2+\nshow that PL can gradually recover by application of pressure. The increase of\nintensity and lifetime with pressure is explained by a reduction of the\nfluorite lattice parameter, a. The variation of Mn2+ PL lifetime with pressure and x is\ndescribed through the same equation by renormalising\nthese parameters to a.<\/p>\n\n\n\n

Author Keywords:<\/strong> high-pressure spectroscopy;\nphotoluminescence; radiationless process; Mn2+;\nfluorite series <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> MN2+ IONS <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Luminescence upconversion mechanisms in Yb3+<\/sup>-Tb3+<\/sup> systems<\/summary>
\n

Author(s):<\/strong> Salley GM, Valiente R, Guedel HU <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 94    Pages:<\/strong>\n305-309     <\/p>\n\n\n\n

Abstract:<\/strong> Tb3+ (D-5(4) –> F-7(3)) luminescence has\nbeen observed in single crystals of SrCl2 : Tb3+ (1%)\n: Yb3+ (1%) and Cs3Tb2Br9 : Yb3+ (1%) under excitation energies in the region\nof Yb3+ absorption. Previous reports of similar systems have postulated two\npossible upconversion mechanisms: (1) cooperative\nsensitization and (2) a sequence of two cooperative absorption steps, or\nGSA\/ESA. We present results of emission. excitation\nand kinetic measurements at low and high temperatures. These measurements allow\nassignment of the mechanism responsible for upconversion\nin these systems. For temperatures greater than T = 100 K process (1) is the\ndominant mechanism, in agreement with previous assignments. However, for T <\n100 K in Cs3Tb2Br9 : Yb3+ (1%), the upconversion occurs through a GSA\/ESA sequence, which is\nshown here in a clear manner for the first time. The efficiency of the\nYb3+-Tb3+ upconversion process for SrCl2\n: Tb3+ (1%) : Yb3+ (1%), at room temperature, under 2.4( 10)W-4\/cm(2),\nis on the order of 10(-4) and decreases with decreasing temperature by four\norders of magnitude. (C) 2001 Elsevier Science B.V. All rights reserved.<\/p>\n\n\n\n

Author Keywords:<\/strong> upconversion;\nTb3-<\/sup>: Yb3+<\/sup> <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong>\nUP-CONVERSION; YB3+ <\/p>\n<\/div><\/details><\/div>\n\n\n\n

EPR study of Cu2+<\/sup> doped (CnH2n+1<\/sub>NH3<\/sub>)(2)CdCl4<\/sub> crystals (n=1;3) with layer structure<\/summary>
\n

Author<\/strong>(s):<\/strong> Valiente R, Rodriguez F, Moreno M, Lezama L <\/p>\n\n\n\n

Source:<\/strong> VIBRONIC INTERACTIONS: JAHN-TELLER EFFECT IN CRYSTALS AND\nMOLECULES   Book\nSeries:<\/strong> NATO SCIENCE SERIES, SERIES II: MATHEMATICS, PHYSICS\nAND CHEMISTRY    Volume:<\/strong> 39    Pages:<\/strong>\n221-228     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the local structure\naround Cu2+, in the two-dimensional perovskite layers\n(CnH2n+1NH3)(2)CdCl4 (n = 1, 3) doped with Cu2+. The\ninterplay between the Jahn-Teller effect and the host\nlattice compressive strain is analyzed through EPR spectroscopy as a function\nof the temperature in both powder and single crystals doped with different Cu2+\nconcentrations. The high tendency Of Cu2+ to form aggregates in these layered\nsystems makes it difficult to study the isolated CuCl64- units. Besides, it is\nshown that Cu2+ replaces Cd2+ by distorting the compressed D-4h site symmetry\nto an elongated rhombic CuCl64- geometry. The long Cu-Cl\naxis is randomly distributed between either of the two equivalent Cd-Cl directions within the layer. The temperature\ndependence of the principal gyromagnetic values and\nthe A(II) hyperfine constant reveal the existence of a\ndynamic Jahn-Teller effect related, not to three\npotential wells as it is usually found in octahedral sites, but to two\npotential wells. This behavior is explained by the energy increase of the\npotential well associated with the out-of-layer Cu-Cl\nelongation, due to site anisotropy. The influence of the D-2h symmetry upon the\nisotropic hyperfine constant is briefly discussed.<\/p>\n\n\n\n

Author Keywords:<\/strong> dynamic and static Jahn-Teller effect; EPR spectroscopy; CU2+ <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CUCL4(NH3)22\nCENTER; SPECTRA <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical properties of A(2)CuCl(4) layer perovskites under pressure. Structural correlations<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF, Hanfland M, Itie JP, Polian A <\/p>\n\n\n\n

Source:<\/strong> FRONTIERS OF HIGH PRESSURE RESEARCH II:\nAPPLICATION OF HIGH PRESSURE TO LOW-DIMENSIONAL NOVEL ELECTRONIC\nMATERIALS   Book\nSeries:<\/strong> NATO SCIENCE SERIES, SERIES II: MATHEMATICS, PHYSICS\nAND CHEMISTRY    Volume:<\/strong> 48    Pages:<\/strong>\n143-153    Published:<\/strong>\n2001   <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the optical spectra of Cu(II) layered perovskites under pressure. The aim is to\nestablish correlations between the metal-to-ligand charge transfer spectra and\nthe local structure around the Cu(II), For this\npurpose, X-ray diffraction (XRD) and X-ray absorption (XAS) experiments on the\ntitle compounds were performed as a function of pressure in the 0-100 kbar\nrange. The pressure redshift experienced by the first charge transfer band\ncorrelates with a reduction of the Janh-Teller (JT) distortion of the\nhexachloride Cu(II) complex. Interestingly, the\napplication of pressure to these layer compounds induces octahedron tilts\nrather than a reduction of the in-plane antiferrodistortive structure related\nto the cooperative JT structure. This reflects the stiffness of the JT Cu\ncomplex whose local bulk modulus is an order of magnitude greater than the\ncrystal bulk modulus.<\/p>\n\n\n\n

Author Keywords:<\/strong> pressure spectroscopy; XAS; XRD;\nJahn-Teller systems; Cu(Il)-layered perovskites <\/p>\n\n\n\n

KeyWords Plus:<\/strong> CL–>CU2+ CHARGE-TRANSFER;\nHYDROSTATIC-PRESSURE; SPECTRA; DIFFRACTION; CU2+; ABSORPTION; SYSTEMS; SERIES;\nK2ZNF4 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

2000<\/strong><\/p>\n\n\n\n

Spectroscopic study and structural characterization of a Li-related photoluminescence center in neutron-irradiated Si<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF, Davies G, Lightowlers EC <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 62    Issue:<\/strong> 10    Pages:<\/strong>\n6180-6191     <\/p>\n\n\n\n

Abstract:<\/strong> We report on a new Li-related photoluminescence\ncenter with zero-phonon line at 879.3 meV. The center\nis created at 550-600 degrees C in the final stages of annealing out\nradiation-induced point defects in float-zone silicon. Isotope and chemical\ncorrelation data establish that the center contains Li and C atoms. The isotope\nshift from Li-6 to Li-7, Delta E = E(Li-7) – E(Li-6) =\n0.18 meV, is similar, per Li atom, to that observed\nfor other Li-related centers in silicon. Uniaxial\nstress measurements establish the symmetry as monoclinic I, with only small\ndepartures from trigonal symmetry. A simple method\nfor the transition is introduced to fit simultaneously the energies,\npolarizations, and relative intensities of the stress-split components. The\ntransition’s dipole is shown to be close to a bonding direction in the plane\nperpendicular to the characteristic [110] axis of the monoclinic I center. The vibronic sideband is produced by coupling to modes of 16,\n31, and 36 meV, with a Huang-Rhys factor S = 1.1.\nThis value can be predicted simply from the uniaxial-stress\ndata. The temperature dependence of the zero-phonon line can be fitted\nprecisely using the spectrum of coupled phonons derived from the vibronic band shape, plus the approximation that the\ndifferences in frequencies of the phonons in the ground and excited electronic\nstates are proportional to the phonon frequency. The luminescence from the\ncenter is reversibly quenched with increasing temperature, with an activation\nenergy E-a = 32+\/-5 meV, however, we show that this\nresult does not arise from the excited state containing a shallow particle.\nAlthough the center is created at 600 degrees C, it is rapidly destroyed at\nroom temperature through passivation by the capture\nof one mobile Li atom.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> UNIAXIAL-STRESS; LUMINESCENCE-CENTERS;\nCRYSTALLINE SILICON; CARBON; LITHIUM; DEFECT; SPECTRUM; ABSORPTION; COMPLEXES;\nBAND <\/p>\n\n\n\n

Reprint Address:<\/strong> Rodriguez, F (reprint author), Univ Cantabria, Fac Ciencias, DCITIMAC, E-39005\nSantander, Spain <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical study of the piezochromic transition in CuMoO4 by pressure spectroscopy<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF, Hernandez D, Garcia-Jaca J, Ehrenberg H, Weitzel H <\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 61    Issue:<\/strong> 24    Pages:<\/strong>\n16497-16501     <\/p>\n\n\n\n

Abstract:<\/strong> The aim of this work is to investigate the\norigin of the piezochromism and thermochromism\nexhibited by the copper oxide CuMoO4. These optical phenomena are associated\nwith structural phase transition (PT) from the triclinic alpha (green)\nmodification to the gamma (brownish-red) modification. The variation of the\noptical-absorption spectrum with pressure and temperature indicates that the piezochromic and thermochromic\ntransitions can be leached from ambient conditions either by applying pressure\nat 2.5 kbar or by cooling at T = 200 K. We show that\nthe change of color at the alpha –> gamma PT is due to the broadening of\nthe first O2- –> Cu2+ charge-transfer band, and the disappearance of an\nintense peak at 1.49 eV, related to the presence of\npyramidal CuO5 complexes in alpha-CuMoO4. The measured oscillator strength\nsuggests that this peak corresponds to the e–>b(1)\ncrystal-field transition within CuO5 rather than to an O2—> Cu2+\ncharge-transfer band. The correlation between optical and structural properties\nperformed in this work confirms this interpretation, and also explains the\nstrong dichroism exhibited by the crystal in the\nhigh-pressure gamma- CuMoO4 modification.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CRYSTAL; PHASE <\/p>\n<\/div><\/details><\/div>\n\n\n\n

A xanes study of the CuK-edge in A(2)CuCl(4) perovskite layers under pressure. Influence of antiferrodistortive structure<\/summary>
\n

Author(s):<\/strong> Rodriguez\nF, Valiente R, Espeso JI, Benfatto M, Pascarelli S <\/p>\n\n\n\n

Source:<\/strong> HIGH PRESSURE RESEARCH    Volume:<\/strong> 18    Issue:<\/strong> 1-6    Pages:<\/strong>\n165-171     <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the X-ray absorption\nspectra of the Cu K-edge in the layered compounds (CnH2n+1NH3)(2)CuCl4\n(n=1-3) and their variation with pressure. The XANES spectra show a three\npeaked structure around 8.98 KeV at zero pressure\nwhich is characteristic of Cu2+ complexes in D-4h symmetry. Application of\nhydrostatic pressure induces a progressive reduction of the energy separation\nbetween the second and third peaks that has been interpreted in terms of a\nprogressive disappearance of the antiferrodistortive\nstructure exhibited by the Cu2+ complexes in this compound series. The results\nare compared with recent pressure experiments on Raman and Charge Transfer\nspectroscopy as well as with Multiple Scattering calculations performed on\nthese layered systems.<\/p>\n\n\n\n

Author Keywords:<\/strong> XANES; pressure spectroscopy; Jahn-Teller; CuCl6 complex; Cu2+-layers; Multiple\nScattering <\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CL–>CU2+\nCHARGE-TRANSFER; SYSTEMS; SPECTRA<\/p>\n<\/div><\/details><\/div>\n\n\n\n

\n\n\n\n

1999<\/strong><\/p>\n\n\n\n

Study of the local structure of Jahn-Teller distorted CuX4<\/sub>2-<\/sup> (X = Cl, Br) systems by polarized charge transfer spectroscopy: Influence of chemical pressure along A2<\/sub>MX4<\/sub> (M = Mn, Zn, Cd, Hg)<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F <\/p>\n\n\n\n

Source:<\/strong> RADIATION EFFECTS AND DEFECTS IN\nSOLIDS    Volume:<\/strong>\n149    Issue:<\/strong>\n1-4    Pages:<\/strong>\n81-87<\/p>\n\n\n\n

 Abstract:<\/strong>\nThe aim of this work is to investigate the Charge Transfer (CT) spectra of\nCuCl42- and CuBr42- complexes formed In Cu2+-doped A(2)MX(4) crystals and their\ndependence with chemical pressure when Cu2+ replaces the divalent cation at the\nMCl42- tetrahedral site. A salient feature of this study is the weak\nsensitivity exhibited by the CT bands to structural changes of the complex. A\nsimilar phenomenon has also been observed for pure chlorocuprates. The analysis\ncarried out on the available family of chlorocuprates indicates that the CT\nband-shift induced by structural distortions in CuCl42- is smaller than that of\nthe corresponding Crystal Field (CF) bands. We present a perturbative model for\nexplaining the weak sensitivity of the CT bands in comparison to the CF ones.\nThe estimates of the model accounts for the spectroscopic results observed\nalong the A(2)MCl(4):Cu2+ series.<\/p>\n\n\n\n

Author Keywords:<\/strong> tetrahedral complex; charge\ntransfer transition; Jahn-Teller distortion; Cucl(4)(2-);\nCuBr4<\/sub>2- <\/sup><\/p>\n\n\n\n

KeyWords Plus:<\/strong> CUCL42 ANIONS; CUBR42 COMPLEXES;\nTRANSFER SPECTRA; TETRACHLOROCUPRATE(II); CRYSTALS; TMA2MNBR4;\nGEOMETRY <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Effects of chemical pressure on the charge-transfer spectra of CuX4<\/sub>2-<\/sup> complexes formed in Cu2+<\/sup>-doped A(2)MX(4) (M=Zn, Mn, Cd, Hg; X=Cl, Br)<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER     Volume:<\/strong> 10    Issue:<\/strong> 42    Pages:<\/strong> 9525-9534<\/p>\n\n\n\n

 Abstract:<\/strong> This work investigates the charge-transfer spectra of CuCl42- and CuBr42- complexes formed in anisotropic A(2)MX(4) (X = Cl, Br) crystals. Attention is paid to the variations of the charge-transfer transition energies induced by chemical pressure effects when substituting Mn –> Zn –> Cd –> Hg along the crystal series. A salient feature of this study is the weak sensitivity of these bands to structural changes of the complex in comparison to the sensitivity of the corresponding crystal field (d-d) bands. The knowledge of these structural-induced shifts is important since they are responsible to a great extent for the thermo- and piezochromic properties exhibited by some compounds containing CuX42- units as chromophores. We present a tentative model based on a perturbed tetrahedral CuX42- complex for explaining the weak sensitivity exhibited by the charge-transfer transitions in the title compounds. Furthermore the estimates of this model can also explain the big difference between the energy shift of d-d and charge-transfer transitions due to structural changes of the CuCl42- complex in pure chlorocuprates.<\/p>\n\n\n\n

Keywords:<\/strong> TRANSFER TRANSITIONS; CUBR42 COMPLEXES; CUCL42 ANIONS; SQUARE-PLANAR; TETRACHLOROCUPRATE(II); CRYSTALS; DISTORTION; TMA2MNBR4; PHASES<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1998<\/strong><\/p>\n\n\n\n

Effects of chemical pressure on the charge-transfer spectra of CuX4<\/sub>2-<\/sup> complexes formed in Cu2+<\/sup>-doped A(2)MX(4) (M=Zn, Mn, Cd, Hg; X=Cl, Br)<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER     Volume:<\/strong> 10    Issue:<\/strong> 42    Pages:<\/strong> 9525-9534<\/p>\n\n\n\n

 Abstract:<\/strong> This work investigates the charge-transfer spectra of CuCl42- and CuBr42- complexes formed in anisotropic A(2)MX(4) (X = Cl, Br) crystals. Attention is paid to the variations of the charge-transfer transition energies induced by chemical pressure effects when substituting Mn –> Zn –> Cd –> Hg along the crystal series. A salient feature of this study is the weak sensitivity of these bands to structural changes of the complex in comparison to the sensitivity of the corresponding crystal field (d-d) bands. The knowledge of these structural-induced shifts is important since they are responsible to a great extent for the thermo- and piezochromic properties exhibited by some compounds containing CuX42- units as chromophores. We present a tentative model based on a perturbed tetrahedral CuX42- complex for explaining the weak sensitivity exhibited by the charge-transfer transitions in the title compounds. Furthermore the estimates of this model can also explain the big difference between the energy shift of d-d and charge-transfer transitions due to structural changes of the CuCl42- complex in pure chlorocuprates.<\/p>\n\n\n\n

Keywords:<\/strong> TRANSFER TRANSITIONS; CUBR42 COMPLEXES; CUCL42 ANIONS; SQUARE-PLANAR; TETRACHLOROCUPRATE(II); CRYSTALS; DISTORTION; TMA2MNBR4; PHASES<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1997<\/strong><\/p>\n\n\n\n

Dependence of the charge transfer spectra of (C2<\/sub>H5<\/sub>NH3<\/sub>)2<\/sub>CdCl4<\/sub>:Cu2+<\/sup> with hydrostatic pressure: Structural changes around Cu2+<\/sup><\/summary>
\n

Author(s):<\/strong> Moral BA, Rodriguez F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS     Volume:<\/strong> 58    Issue:<\/strong> 9    Pages<\/strong>: 1487-1490<\/p>\n\n\n\n

 Abstract:<\/strong> This paper investigates the variation of the charge transfer (CT) spectra of the Cu2+ doped (EtNH3)(2)CdCl4 (Et = C2H5) layer perovskite under hydrostatic pressure. The aim is to explain the strong redshift (-4000 cm(-1)) undergone by the first CT band of the formed CuCl64- complex on passing from (EtNH3)(2)CdCl4: Cu2+ to the isomorphous (EtNH3)(2)MnCl4: Cu2+ crystal, which is accompanied by a change of color from light yellow to deep red. The pressure experiments show that the first Cl- –> Cu2+ CT band experience an abrupt shift of -1200 cm(-1) between 23 and 26 kbar. The comparison of these results with those previously obtained in the pure (EtNH3)(2)CuCl4 suggests that this shift is associated with a local change around the Cu2+ from an elongated octahedron geometry (P = 1 atm) to a more compressed situation similar to that found for the Mn crystal. (C) 1997 Elsevier Science Ltd. All rights reserved.<\/p>\n\n\n\n

Keywords:<\/strong> CHLORIDE; TRANSITIONS; DISTORTION; ABSORPTION; CRYSTALS; K2ZNF4; ION<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Local structure of Cu2+<\/sup> in the (C2<\/sub>H5<\/sub>NH3<\/sub>)2<\/sub>MCl4<\/sub>:Cu2+<\/sup> (M=Cd, Mn) layer perovskites. IStudy of bidimensional (CH3<\/sub>NH3<\/sub>)2<\/sub>CdCl4<\/sub>: Cu2+<\/sup> and (CH3<\/sub>NH3<\/sub>)2<\/sub>CuCl4<\/sub><\/summary>
\n

Author(s):<\/strong> Moral BA, Rodriguez F, Valiente R, Valiente R, Lezama LM, Rodriguez F, Moreno MU<\/p>\n\n\n\n

Source:<\/strong> PROCEEDINGS OF THE 13TH INTERNATIONAL CONFERENCE ON DEFECTS IN INSULATING MATERIALS – ICDIM 96 MATERIALS SCIENCE FORUM    Volume:<\/strong> 239    Issue:<\/strong>     Pages<\/strong>: 729-732<\/p>\n\n\n\n

 Abstract:<\/strong> <\/p>\n\n\n\n

The bidimensional (CH3NH3)(2)CdCl4 lattice containing isolated Cu2+ ions has been explored through the charge transfer and EPR spectra obtained in the 10 – 300 K temperature range. Both spectra are consistent with the existence of two different sites for Cu2+, but where the same D-2h CUCl64- center is formed. The longest and the intermediate Cu2+-Cl- bonds of the complex are alternated in the layer (a,b) plane, while the shortest bond is the c direction perpendicular to the layer. The temperature dependence of the EPR spectra demonstrates the existence of dynamic features associated with two (and not three) equivalent wells on a given site. All these features are consistent with the existence of an additional strain term (reflecting the bidimensional host lattice), as well as the usual Jahn-Teller term in cubic symmetry.<\/p>\n\n\n\n

The importance of this fact for a possible transition to a D-4h compressed geometry under pressure is discussed. The EPR spectrum of (CH3NH3)(2)CUCl4 in the (a,b) plane is isotropic due to the exchange interaction between the two Cu2+ sites.<\/p>\n\n\n\n

Keywords:<\/strong> Jahn-Teller effect; two equivalents wells; charge transfer bands<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Local structure of Cu2+<\/sup> in the (C2<\/sub>H5<\/sub>NH3<\/sub>)2<\/sub>MCl4<\/sub>:Cu2+<\/sup> (M=Cd, Mn) layer perovskites. Influence of hydrostatic pressure in the 0-60 kbar range<\/summary>
\n

Author(s):<\/strong>Moral BA, Rodriguez F, Valiente R, Moreno M, Gudel HU<\/p>\n\n\n\n

Source:<\/strong> ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS     Volume:<\/strong> 201    Issue:<\/strong>     Pages<\/strong>: 151-158<\/p>\n\n\n\n

 Abstract:<\/strong> This paper deals with the effects of pressure on the charge-transfer spectra of CuCl64- complexes formed in Cu2+ doped (C2H5NH3)(2)MCl4 (M = Cd, Mn). A pressure-induced redshift is observed for the first charge-transfer band in both crystals. While the shift is continuous for the Mn crystal at a rate of -40 cm(-1)\/kbar in the 0-60 kbar range, it experiences an abrupt jump of -1400 cm(-1) around 26 kbar for the Cd crystal. Such a discontinuous behaviour is interpreted in terms of a structural change in the CuCl64- coordination geometry from an axially elongated octahedron to a more compressed geometry. The present results are compared with those reported for the pure (C2H5NH3)(2)CuCl4 crystal.<\/p>\n\n\n\n

Keywords:<\/strong> charge-transfer spectroscopy; hydrostatic pressure; CuCl6<\/sub>4-<\/sup>-complex;; (C2<\/sub>H5<\/sub>NH3<\/sub>)2<\/sub>MnCl4  <\/sub>(C2<\/sub>H5<\/sub>NH3<\/sub>)2<\/sub>CdCl4 <\/sub> <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Thermally-induced dichroism in Cu2+<\/sup> doped [(CH3<\/sub>)4<\/sub>N]HgBr3<\/sub>: Study of the thermochromic properties<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez F<\/p>\n\n\n\n

Source:<\/strong> ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS     Volume:<\/strong> 201    Issue:<\/strong>     Pages<\/strong>: 159-164<\/p>\n\n\n\n

 Abstract:<\/strong> <\/p>\n\n\n\n

This work investigates the polarized Charge-transfer spectra associated with Cu2+ impurities in [(CH3)(4)N]HgBr3:Cu2+ in the 10-300 K temperature range. Attention is paid for correlating the optical spectra with the local structure around Cu2+. The spectra are compared with those obtained in the Cu2+ doped [(CH3)(4)N]CdBr3 and [(CH3)(4)N]MnBr3, and [(CH3)(4)N](2)HgBr4 and [(CH3)(4)N](2)CdBr4 crystals, where the Cu2+ ions form CuBr64- complexes of nearly D-4h symmetry and tetrahedral distorted CuBr42–complexes of D-2d symmetry, respectively. The presence of a strongly-polarized absorption band at 15900 cm(-1) in [(CH3)(4)N]HgBr3:Cu2+ is interpreted in terms of a highly distorted CuBr42- complex. The enhancement of dichroism exhibited by this crystal with decreasing temperature is noteworthy. The analysis of the spectra reveals that this unusual thermal behaviour is mainly associated with orientational motions of the Cu2+ complex rather than with structural changes of the complex.<\/p>\n\n\n\n

Keywords:<\/strong> charge-transfer spectra; Cu2+ impurities; copper bromide complexes <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Synthesis, structure and polarized optical spectroscopy of two new fluoromanganese(III) complexes<\/summary>
\n

Author(s):<\/strong> N\u00fa\u00f1ez P, Elias C<\/a>, Fuentes J, Solans X, Tressaud A, deLucas MCM, Rodr\u00edguez F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS    Volume:<\/strong>     Issue:<\/strong> 22    Pages<\/strong>: 4335-4340<\/p>\n\n\n\n

 Abstract:<\/strong> The syntheses and crystal structures of two new fluoromanganese(III) complexes are reported; [MnF3(H2O)(2, 2′-bipy)] 1 and 4, 4′-bipyH(2)[MnF4(H2O)(2)].2H(2)O 2, where 2, 2′-bipy and 4, 4′-bipy are 2, 2′-bipyridyl and 4, 4′-bipyridyl, respectively. Compound 1: monoclinic, space group P2(1)\/n, a = 1973.7(4), b = 749.0(2), c = 903.1(3) pm, beta = 95.22(3)degrees, Z = 4, R1 = 0.051. Compound 2: monoclinic, space group P2(1), a = 516.4(2), b = 1851.9(4), c = 986.3(3) pm, beta = 99.07(2)degrees, Z = 2, R1 = 0.028. The manganese co-ordination environment was found to be octahedral in both compounds, but strongly distorted by the Jahn-Teller effect as a result of the high-spin d(4) configuration of Mn3+. A very extensive intermolecular hydrogen-bond framework is present in both compounds. For compound 1 the octahedra are linked through hydrogen bridges resulting in octahedral manganese chains. For compound 2, the octahedra [MnF4(H2O)(2)](-) are associated via hydrogen bonds into chains, which in turn are connected by interchain hydrogen bridges. The polarized optical spectra of single crystals are presented and explained in terms of intraconfigurational d(4) transitions split by ligand fields of nearly C-s and D-4h symmetries for compounds 1 and 2, respectively. The results are compared with those available for other Mn-III fluorides.<\/p>\n\n\n\n

Keywords:<\/strong> MAGNETIC-STRUCTURES; CRYSTAL-STRUCTURE; ALKALI-METAL; MANGANESE(III); FLUORIDES; COMPOUND <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1996<\/strong><\/p>\n\n\n\n

Polarized electronic spectra of the (CH3<\/sub>NH3<\/sub>)2<\/sub>Cd1-xMnxCl4<\/sub> (x=0-1) perovskite layer with CU2+ :Study<\/sup> of the Cl–>CU2+<\/sup> charge transfer intensity enhancement along the series<\/summary>
\n

Author(s):<\/strong> Valiente R, Rodriguez <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS     Volume:<\/strong> 57    Issue:<\/strong>     Pages<\/strong>: 571-587<\/p>\n\n\n\n

 Abstract:<\/strong> The polarized optical absorption spectra of the 2-D A(2)Cd(1-x)Mn(x)Cl(4) (x = 0-1; A = CH3NH3) crystals doped with Cu2+ investigated. The analysis of both the charge transfer and crystal field spectra indicates that the copper impurities form CuCl64- complexes with an elongated D-2h (nearly D-4h) symmetry. A salient feature is the enhancement of charge transfer band intensity as well as the presence of new intense bands at 21000 and 25000 cm(-1) observed on passing from x = 0 to x = 1 along the series. These bands are associated with Mn-Cu aggregates whose superexchange pathways involve the short (equatorial) Cu-Cl bond (25000 cm(-1)) and the long (axial) Cu-Cl bond (21000 cm(-1)) of the CuCl64- complex. A noteworthy fact of these exchange coupled Mn-Cu systems is that the transition energy of the first Mn2+ excitations are resonant with the Cl- –> Cu2+ charge transfer transitions. This effect seems to play a fundamental role in the enhancement of intensity. The temperature dependence of the oscillator strength allowed us to estimate a ground state exchange constant J approximate to 70 cm(-1) for the Mn-Cu pair. The results are compared with those obtained in Mn-Cu aggregates in fluorides.<\/p>\n\n\n\n

Keywords:<\/strong> CuCl64-; exchange coupled Mn-Cu systems; charge transfer spectra; (RNH(3))(2)Cd1-xMnxCl4 crystals; spectroscopic and structural correlations <\/p>\n<\/div><\/details><\/div>\n\n\n\n

Luminescence from BaF2:Mn2+ samples: Substitutional Mn2+ ions are ‘silent’<\/summary>
\n

Author(s):<\/strong> deLucas MCM, Moreno M, Rodr\u00edguez F, Baranov PG<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER     Volume:<\/strong> 8   Issue:<\/strong>  14  Pages<\/strong>: 2457-2465<\/p>\n\n\n\n

 Abstract:<\/strong> Through this work it is shown Chat the luminescence observed in BaF2:Mn2+ samples is related to the formation of BaMnF4 microcrystalline precipitates. This conclusion is supported by the experimental emission and excitation spectra as well as by the temperature dependence displayed by the emission intensity. Also the EPR spectrum of most doped samples clearly shows the presence of a signal (superimposed on that coming from isolated Mn2+ ions) whose temperature dependence is similar to that displayed by BaMnF4 crystals. The absence of luminescence associated with isolated Mn2+ ions in the BaF2 host lattice is discussed. It is pointed out that luminescence quenching is probably related to a multiphonon non-radiative process rather than to a T-4(1) (G) excited state close to the bottom of the BaF2 conduction band. Although luminescence quenching appears for a Dexter-Klick-Russell parameter A probably close to 0.1, this is qualitatively related to a high radiative lifetime (tau(R) similar or equal to 100 ms). The analysis made also shows that firstly Lambda increases by a factor of about 1.7 on going from Mn2+-doped fluoroperovskites to Mn2+ in fluoride-type crystals, and secondly Lambda increases on going from CaF2 : Mn2+ to SrF2 : Mn-2. Both variations mainly reflect a parallel increase in the Stokes shift.<\/p>\n\n\n\n

Keywords:<\/strong> LOCAL INSTABILITY; LATTICES; PHOTOLUMINESCENCE; RELAXATION; ABSORPTION; CRYSTALS; DISTANCE; FLUORIDE; IMPURITY; SPECTRUM<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1995<\/strong><\/p>\n\n\n\n

Polarized charge transfer spectra of Cu2+<\/sup> doped perovskite layers (RNH3<\/sub>)2<\/sub>CdxMn1-xCl4<\/sub> (x=0-1)<\/summary>
\n

Author(s):<\/strong> Baticle B, Rodriguez F, Valiente R<\/p>\n\n\n\n

Source:<\/strong> RADIATION EFFECTS AND DEFECTS IN SOLIDS       Volume:<\/strong> 135  Issue:<\/strong>  1-4  Pages<\/strong>: 587-592<\/p>\n\n\n\n

 Abstract:<\/strong> <\/p>\n\n\n\n

This work investigates the charge transfer spectra of CuCl64- complexes formed in the (RNH(3))(2)CdxMn1-xCl4 crystal series. For x = 1, it is demonstrated that Cu complexes display an elongated D-4h symmetry, forming an antiferrodistortive type structure which is similar to that found in the pure copper crystals. The presence of Mn induces an important enhancement of the charge transfer bands as well as significant redshifts. The results are interpreted in terms of distortions of the CuCl64- geometry which changes from D-4h elongated (x = 1) to nearly D-4h compressed (x = 0). The transition energy, polarization and assignment of the charge transfer bands are analysed.<\/p>\n\n\n\n

Keywords:<\/strong> CuCl64- comples; D-4h elongated and compressed symmetries; charge transfer spectra; (RNH(3))(2)CdxMn1-xCl4 crystals<\/p>\n<\/div><\/details><\/div>\n\n\n\n

NEW DOUBLE-BEAM SPECTROPHOTOMETER FOR MICROSAMPLES – APPLICATION TO HYDROSTATIC-PRESSURE EXPERIMENTS<\/summary>
\n

Author(s):<\/strong> MORAL BA, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> REVIEW OF SCIENTIFIC INSTRUMENTS      Volume:<\/strong> 66  Issue:<\/strong>  11  Pages<\/strong>: 5178-5182<\/p>\n\n\n\n

 Abstract:<\/strong> This article describes a new double beam spectrophotometer specially conceived for optical absorption measurements on low-absorbing microsamples. The available long-working distance makes this apparatus attractive for use on samples placed in special environments such as heating stages, biological cells, and particularly hydrostatic pressure cells. Its performance has been tested in optical absorption measurements for different Mn2+ and Cu2+ complexes. We applied the instrument for investigating the electronic spectrum of Cu2+ doped (CH3CH2NH3)(2)CdCl4 crystals under hydrostatic pressure using a Sapphire anvil cell. A salient feature of this work is the enormous redshift (1400 cm(-1)) experienced by the first Cl- –> Cu2+ charge transfer band at 26 kbar. We briefly comment on the origin of this shift. (C) 1995 American Institute of Physics.<\/p>\n\n\n\n

Keywords:<\/strong> DIAMOND-ANVIL CELL; PHASE-TRANSITIONS; CRYSTALS; SYSTEM<\/p>\n<\/div><\/details><\/div>\n\n\n\n

CHARGE-TRANSFER SPECTRA AND DYNAMICS OF CUBr4<\/sub>2-<\/sup> IN [N(CH3<\/sub>)4<\/sub>]2<\/sub> CUBr4<\/sub>2-<\/sup> CU2+<\/sup> CRYSTALS – A NEW FIRST-ORDER PHASE-TRANSITION AT T-C2=20 K<\/summary>
\n

Author(s):<\/strong> VALIENTE R, DELUCAS MCM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER      Volume:<\/strong> 7 Issue:<\/strong>  20  Pages<\/strong>: 3881-3894<\/p>\n\n\n\n

Abstract:<\/strong> The charge-transfer electronic structure of CuBr42- in [N(CH3)(4)]2CdBr4 crystals is investigated through polarized optical absorption spectroscopy. The transition energy and the band polarization are explained in terms of the Jahn-Teller distortions of D-2d symmetry of the CuBr42- complex. Some bands are split in the low-temperature spectra by the spinorbit interaction of the Br ligands. The results are compared with those available for other CuBr42- systems. We also investigate the dynamics of the inorganic CuBr42- units in the 9.5-300 K temperature range through the intensity of the charge-transfer bands. Analogously to the CdBr42- tetrahedra in the pure crystal, CuB42- experiences reorientational motions upon varying the temperature which are correlated with the temperature dependence of the monoclinic beta parameter below the Pmcn –> P2(1)\/c phase transition temperature T-cl = 272 K. An important finding of the present work is the observation of anomalies in the CuBr42- dynamics which are associated with the existence of a new first-order phase transition at T-c2 = 20 K with a thermal hysteresis Delta T = 10 K. This new phase transition, which had not previously been detected in the [(CH3)(4)N](2)MBr(4) (M = Zn, Mn, Co or Cd) series, would correspond to the monoclinic P2(1)\/c to orthorhombic P2(1)2(1)2(1) transition, confirming the predictions of the universal p-T phase diagrams of the title compounds.<\/p>\n\n\n\n

Keywords:<\/strong> TRANSFER BANDS; CUCL42 ANIONS; TETRACHLOROCUPRATE(II); DISTORTION; CONNECTION; NH4CL-CU2+; TMA2MNBR4; COMPLEXES; CO; CU<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Spectroscopic study of Cr3+<\/sup> in new elpasolites<\/summary>
\n

Author(s):<\/strong> DeLucas MCM, Dance JM, Rodriguez F, Tressaud A, Moreno M, Grannec J <\/p>\n\n\n\n

Source:<\/strong> RADIATION EFFECTS AND DEFECTS IN SOLIDS      Volume:<\/strong> 135 Issue:<\/strong> 1-4  Pages<\/strong>: 517-520<\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

New elpasolites like A2KMF6 doped with Cr3+<\/sup> have been investigated by means of optical and EPR techniques. It is shown that though the structural phase transition undergone by Rb2KGaF6 at T = 129 K is much stronger than that corresponding to Rb2KInF6, the emission band at 10 K of the latter is much broader than that for the former. This inhomogeneous broadening is correlated with the increase experienced by the EPR bandwidth below 150 K reflecting only local changes around Cr3+. An analysis of zero phonon lines through the fluoroelpasolite series reveals that they are very sensitive to changes of the Cr3+-F- distance, R. It is shown that changes Delta R(o) in the perfect lattice induce changes on R given by Delta R = fR(o) where fis only 0.15. At variance with the findings for MnF64-, the present results indicate that an increase of R tends to decrease the Stokes shift. The origin of this fact is discussed. Finally, the present results indicate that R increases (about 0.2 pm) in the phase transition of Rb2KGaF6 although the lattice volume decreases.<\/p>\n\n\n\n

Keywords:<\/strong> fluoroelpasolites doped with Cr3+; luminescence of Cr3+; EPR of Cr3+; phase transitions; influence of the Cr-F distance<\/p>\n<\/div><\/details><\/div>\n\n\n\n

Optical properties and local structure of MnCl6<\/sub>4-<\/sup> in ABCl3<\/sub>:Mn2+<\/summary>
\n

Author(s):<\/strong> DeLucas MCM<\/a>, Rodriguez F<\/a>, Prieto C<\/a>, Verdaguer M<\/a>, Moreno M<\/a>, Gudel HU<\/a><\/p>\n\n\n\n

Source:<\/strong> RADIATION EFFECTS AND DEFECTS IN SOLIDS      Volume:<\/strong> 135 Issue:<\/strong> 1-4  Pages<\/strong>: 593-598<\/p>\n\n\n\n

Abstract:<\/strong> The optical properties of ABCl(3):Mn2+ crystals are investigated in the 300-10 K temperature range. The variation of the peak energy and the Stokes shift along the series are explained in terms of slight differences in the Mn-CI distance. The local structure around the Mn is determined by correlating optical spectroscopy and EXAFS techniques. Interestingly, the thermal shift of the (6)A(1g) –> T-4(1g) excitation band is much smaller than that experienced by the corresponding emission band. This behaviour is explained by the phonon assisted mechanism involve in these transitions. The influence of the structural phase transition of the CsCaCl3:Mn2+ at T-C = 95 K upon the thermal band shift is also analysed.<\/p>\n\n\n\n

Keywords:<\/strong> excitation and luminescence; ABCl(3):Mn2+ perovskites; MnCl64- complex; thermal shift; local structure around Mn2+; influence of bond distances<\/p>\n<\/div><\/details><\/div>\n\n\n\n

EXCITATION AND EMISSION THERMAL SHIFTS IN ABF3<\/sub>MN2+<\/sup> PEROVSKITES – COUPLING WITH IMPURITY VIBRATIONAL-MODES<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER      Volume:<\/strong> 7 Issue:<\/strong> 38  Pages<\/strong>: 7535-7548 <\/p>\n\n\n\n

Abstract:<\/strong> The thermal shifts undergone by the first moment of the (6)A(1g)(S) –> T-4(1g)(G) excitation band and the associated emission band of Mn2+-doped ABF(3) perovskites are investigated in the 9-300 K temperature range. It is found that these shifts are similar for the whole series and have average values of +150 and +450 cm(-1) for excitation and emission, respectively. Both the sign and the magnitude of these different thermal shifts are explained in terms of (i) the phonon assistance mechanism required to gain intensity of the parity-forbidden transitions, (ii) the quadratic electron-phonon coupling and (iii) thermal expansion effects. To achieve this analysis a previous discussion upon the nature of the vibrational modes seen in the optical spectra is carried out. It is stressed that the impurity vibrational mode displaying HBAR omega(g) = 570 cm(-1) in the emission spectrum of KMgF3:Mn2+ exhibits a value of 540 cm(-1) in the corresponding excitation spectrum. This situation, which is also found for other modes seen in the optical spectra of KMgF3:Mn2+, indicates that the mode (though associated with the LO(3) branch of KMgF3) is not a pure mode of the lattice but displays a kind of resonant character. As a salient feature the calculated thermal shifts are based on the experimental shifts experienced by the frequencies of the optical and acoustic modes on going from the ground (6)A(1g) to the excited T-4(1g) state of MnF64-. At variance with findings for the R lines in Cr3+ and V2+, it is clearly demonstrated that the explicit and implicit contributions to the thermal shift of the zero-phonon line in MnF64- are similar and both induce red shifts upon heating. Moreover the present analysis reveals that the explicit contribution to the thermal shift undergone by the zero-phonon line of KMgF3:Mn2+ is mainly dominated by the odd-parity low-energy modes. The calculated thermal shifts reproduce reasonably well the experimental data.<\/p>\n\n\n\n

Keywords:<\/strong> TEMPERATURE-DEPENDENCE; 2-EXCITON BANDS; RBMNF3; KMGF3; PHOTOLUMINESCENCE; TRANSITIONS; KZNF3; K2NAGAF6-CR3+; ABSORPTION; SPECTRUM<\/p>\n<\/div><\/details><\/div>\n\n\n\n

LOCAL-STRUCTURE DETERMINATION OF MN2+ IN THE ABCL3<\/sub>MN2+<\/sup> CHLOROPEROVSKITES BY EXAFS AND OPTICAL SPECTROSCOPY<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS      Volume:<\/strong> 56 Issue:<\/strong> 7  Pages<\/strong>: 995-1001 <\/p>\n\n\n\n

Abstract:<\/strong> This work reports the local structure around the manganese in the ABCl(3):Mn2+ (A = K, Rb, Ca and B = Mg, Ca, Cd, Sr) chloroperovskite series. EXAFS and XANES experiments carried out in KMgCl3:Mn2+ and RbCaCl3:Mn2+ indicate that the Mn-Cl distances of the MnCl64- complex are 2.51 and 2.53 Angstrom, respectively. These values are very similar to those found in the pure NH4MnCl3 perovskite, R = 2.525 Angstrom, and show that the variations of R along the series do not follow that of the host lattice. The correlation between these measurements and the optical excitation spectra allows us to estimate Mn-Cl bond distances for the whole series with accuracies of about 0.002 Angstrom. The present results are compared with previous structural data reported for the ABF(3):Mn2+ isomorphous fluorides.<\/p>\n\n\n\n

Keywords:<\/strong> XAFS (EXAFS AND XANES); CRYSTAL FIELDS; LUMINESCENCE; OPTICAL PROPERTIES; INORGANIC COMPOUNDS<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1994<\/strong><\/p>\n\n\n\n

AN INSIGHT INTO OPTICAL AND EPR PROPERTIES OF AgCL6<\/sub>4-<\/sup>AND AgF6<\/sub>4-<\/sup> COMPLEXES THROUGH MS-X-ALPHA AND SCCEH CALCULATIONS<\/summary>
\n

Author(s):<\/strong> VALIENTE R, ARAMBURU JA, BARRIUSO MT, MORENO M<\/p>\n\n\n\n

Source:<\/strong> INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY   Volume:<\/strong> 52 Issue:<\/strong> 4  Pages<\/strong>: 1051-1065 <\/p>\n\n\n\n

Abstract:<\/strong> MS-Xalpha and SCCEH calculations on the Ag2+ complexes AgF6(4-) and AgC6(4-) (displaying an elongated D4h symmetry) have been carried out for a better understanding of their experimental optical and EPR properties. As salient features, the present work supports that the unpaired electron in AgCl6(4-) spends a little more time on ligands than on Ag2+, in agreement with the previous analysis of EPR and optical data for KCl:Ag2+. Furthermore, the five experimental optical transitions observed in that case are reasonably assigned. The first transition (observed at 12,500 cm-1) is assigned to a jump involving the 5a1g orbital built mainly (approximately 70%) from 3p orbitals of axial ligands, a fact that reflects the distinct level scheme for AgCl6(4-) when compared to that for more ionic complexes. Calculations on AgF6(4-) and AgF4(2-) performed as a function of the equatorial Ag2+ – F- distance led to a reasonable understanding of experimental gyromagnetic and superhyperfine tensors displayed by Ag2+ in fluorides. The different relative decrease undergone by g(parallel-to) – g0 (8%) and g(perpendicular-to) – g0 (28%) on passing from CsCdF3:Ag2+ to RbCdF3:Ag2+ is shown to be consistent with the formation of AgF6(4-) and AgF4(2-) complexes, respectively, related to the different substitutional position of Ag2+ in such lattices. The decrement of about 8.5% experienced by both g(parallel-to) – g0 and g(perpendicular-to) -g0 values on going from CsCdF3:Ag2+ to NaF:Ag2+ is pointed out to reflect the different electrostatic potential (exerted by the rest of the lattice upon the complex) seen by AgF6(4-) embedded in NaCl or perovskite-type lattices. (C) 1994 John Wiley & Sons, Inc.<\/p>\n\n\n\n

Keywords:<\/strong> ELECTRON-PARAMAGNETIC-RESONANCE; CHARGE-TRANSFER TRANSITIONS; CUCL42; NI+; ABSORPTION; COPPER(II); IMPURITIES; PARAMETERS; SPECTRUM; LATTICE<\/p>\n<\/div><\/details><\/div>\n\n\n\n

ELECTRONIC-STRUCTURE OF Ag2+<\/sup> IMPURITIES IN HALIDE LATTICES<\/summary>
\n

Author(s):<\/strong> VALIENTE R, ARAMBURU JA, BARRIUSO MT, MORENO M <\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER    Volume:<\/strong> 6 Issue:<\/strong> 24  Pages<\/strong>: 4515-4525 <\/p>\n\n\n\n

Abstract:<\/strong> The composition of electronic levels as well as optical transitions associated with AgCl6(4-) and AgF6(4-) complexes have been studied through MS-Xalpha and SCCEH calculations performed as a function of equatorial (R(eq)) and axial (R(ax)) metal-ligand distances. The scheme and composition of levels for AgCl6(4-) is rather different from that for AgF6(4-) and other more ionic systems. The first transition for KCl:Ag2+ (observed at 12 500 cm-1) is assigned to a jump involving the 5a1g orbital which is mainly built (about 70%) from 3p orbitals of axial chlorine atoms. Aside from explaining reasonably the five optical bands experimentally observed for KCl:Ag2+, the present work indicates that the first allowed charge-transfer transition of AgF6(4-) would lie in the ultraviolet region and confirms that the unpaired electron in AgCl6(4-) spends a little more time on equatorial ligands than on the central ion. All these results are consistent with a high value (chi = 2.8) for the optical electronegativity of Ag2+. The dependence of electronic transitions (and also of unpaired spin densities f(sigma) and f(s)) on R(eq) and R(ax) is found to be rather similar for both AgF6(4-) and AgCl6(4-) complexes. The relation between such a dependence and the band widths of optical transitions is outlined.<\/p>\n\n\n\n

Keywords:<\/strong> CHARGE-TRANSFER TRANSITIONS; X-ALPHA CALCULATIONS; OPTICAL-SPECTRUM; PARAMAGNETIC-RES; SQUARE-PLANAR; COMPLEXES; COPPER; CUCL42; ABSORPTION; PARAMETERS<\/p>\n<\/div><\/details><\/div>\n\n\n\n

POLARIZED CHARGE-TRANSFER SPECTROSCOPY OF CU2+<\/sup> IN DOPED ONE-DIMENSIONAL [N(CH3<\/sub>)4<\/sub>]CdCl3<\/sub> AND [N(CH3<\/sub>)4<\/sub>]CdBr3<\/sub><\/summary>
\n

Author(s):<\/strong> VALIENTE R, DELUCAS MCM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER     Volume:<\/strong> 6 Issue:<\/strong> 24  Pages<\/strong>: 4527-4540 <\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

This work investigates the polarized charge-transfer (CT) spectra of the Jahn-Teller distorted CuCl6(4-) and CuBr6(4-) complexes formed in Cu2+-doped [N(CH3)4]CdCl3 and [N(CH3)4]CdBr3 CrYstals. The transition energies as well as the dominant polarization of the CT bands along the hexagonal c direction are explained in terms of rhombic D2h distortions. In the bromide complexes, the strong spin-orbit interaction of the Br- ligands leads to additional bands in the low-temperature spectra. Evidence of vibronic couplings to totally symmetric vibrations is found from analysis of the temperature dependence of the band width. The influence of Cu2+<\/sup> impurities in the lattice dynamics is studied through the variation undergone by different spectroscopic parameters in the 10-300 K range. Throughout this work, the high sensitivity of CT transitions for detecting the structural phase transitions exhibited by these crystals is demonstrated. In particular, the enhancement of the first-order character of the ferroelectric phase transition in [N(CH3)4]CdBr3:Cu2+ at T(F) = 157 K, which has been associated with the presence of Cu2+ impurities is worth noting.<\/p>\n\n\n\n

Keywords:<\/strong> STRUCTURAL PHASE-TRANSITIONS; TRANSFER SPECTRA; EMISSION DYNAMICS; TRANSFER BANDS; SQUARE-PLANAR; CRYSTALS; ABSORPTION; LATTICE; TMMC; NH4CL-CU2+<\/p>\n<\/div><\/details><\/div>\n\n\n\n

THE INFLUENCE OF A 2ND-ORDER PHASE-TRANSITION ON IMPURITY LUMINESCENCE – A STUDY OF RBCDF3<\/sub>MN-2+<\/sup><\/summary>
\n

Author(s):<\/strong> DELUCAS MCM<\/a>, RODRIGUEZ F<\/a>, MORENO M<\/a>, TRESSAUD A<\/a><\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER    Volume:<\/strong> 6 Issue:<\/strong> 11  Pages<\/strong>: 6353-6366 <\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

Precise photoluminescence measurements have been carried out on RbCdF3:Mn2+ in the 9-300 K range to explore the structural phase transition of the host lattice at T(c) = 124 K using the first (M1) and second (M2) moments of the emission band together with the lifetime r as probes. Aside from showing a sensitivity of M2(T) and r(T) to the phase transition, the present data reveal that the curve M1(T) experiences a small but observable change of slope in the vicinity of T(c). It is demonstrated that this jump, DELTA(t)(partial derivative M1\/partial derivative T)p = 0.22 cm-1 K-1, is mainly associated with the increase experienced by the local thermal expansion coefficient below T(c). The importance of both the implicit and explicit contributions to M1 (T) is analysed throughout this work.<\/p>\n\n\n\n

Neither the luminescence nor the excitation spectrum shows any evidence of tetragonal distortion in the MnF64- complex. This fact is explained through the R(ax) – R(eq) = 0.2 pm value (where R(ax) and R(eq) are the axial and equatorial Mn2+-F- distances) at 30 K, and the coupling coefficient V(E) = 66 cm-1 pm-1 with the E(g) Jahn-Teller mode of MnF64-. Finally, we have found that this crystal exhibits photochemical reactions under uv light irradiation, leading to the formation of centres that transfer easily to Mn2+ ions. These centres give rise to an intense absorption band at 310 nm, analogously to those previously formed under x-irradiation.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> TEMPERATURE-DEPENDENCE; RBMNF3; KZNF3; FLUOPEROVSKITES; CRYSTALS; CONSTANT; RBCAF3; CSCAF3<\/p>\n<\/div><\/details><\/div>\n\n\n\n

ZERO-PHONON TRANSITIONS AND THE STOKES SHIFT OF MN2+<\/sup>-DOPED PEROVSKITES – DEPENDENCE ON THE METAL-LIGAND DISTANCE<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM<\/a>, RODRIGUEZ F<\/a>, MORENO M<\/a><\/a><\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 50 Issue:<\/strong> 5  Pages<\/strong>: 2760-2765 <\/p>\n\n\n\n

Abstract:<\/strong> This work reports the excitation and luminescence spectra at T = 9 K of the Mn2+-doped RbCdF3, RbCaF3, and CsCaF3 fluoroperovskites. A Mn2+ concentration down to 400 ppm has been detected. The present data together with those available for KMgF3:Mn2+, KZnF3:Mn2+, KMnF3, and RbMnF3, allow us to explore the variations of the zero-phonon line (ZPL) and the Stokes shift [associated with the Mn2+ luminescent 4T1g (G) –> 6A1g (S) transition] along the whole series of cubic fluoroperovskites doped with Mn2+ in order to investigate their dependence with the Mn-F distance, R. The experimental variation of the ZPL energy measured in the 206-215 pm range is E(ZPL) = -21 305 + 187R (pm). This strong dependence of ZPL upon R allows one to measure Mn-F distances along the series of fluoroperovskites with accuracies of better than 0.001 angstrom, thus improving by more than one order of magnitude the extended x-ray-absorption fine structure resolution. Furthermore, this sensitivity is extended down to 10(-4) angstrom when we analyze the variations deltaR induced by pressure in a given system. As regards DELTAE(s), the present results on Mn2+-doped fluoroperovskites demonstrate an increase of the Stokes shift when R increases. This behavior is explained to be related to a Gruneisen constant gamma(a1g) corresponding to the symmetric mode of the complex. The value of the constant is greater than 1.9, in agreement with calculations on divalent transition-metal complexes like MnF64- and VF64-. The importance of the present results for the observation of luminescence through the full series of Mn2+-doped fluoroperovskites is also discussed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> TEMPERATURE-DEPENDENCE; PHASE-TRANSITIONS; OPTICAL-SPECTRUM; MN-2+-F DISTANCE; PRESSURE; KZNF3; LUMINESCENCE; RBMNF3; PHOTOLUMINESCENCE; K2NAGAF6-CR3+<\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMINESCENCE STUDY OF NA6<\/sub>MNCL8<\/sub> AND NA6<\/sub>MNBR8 <\/sub>MICROCRYSTALS IN NACL AND NABR LATTICES<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> PHYSICA STATUS SOLIDI B-BASIC RESEARCH    Volume:<\/strong> 184 Issue:<\/strong> 1  Pages<\/strong>: 247-265 <\/p>\n\n\n\n

Abstract:<\/strong> A detailed study of the luminescence and excitation spectra as well as of the lifetime (tau) on Na6MnX8 (X = Cl, Br) precipitates in the 300 to 2 K temperature range is made. In spite of the large distance between nearest Mn2+ ions (0.797 nm for Na6MnCl8), it is demonstrated that even at 2 K luminescence takes place at excitation traps after an exchange induced transfer between close Mn2+ ions. At variance to compounds like MnF2, only one trap (with depth of 350 and 480 cm-1 for X = Cl and Br, respectively) together with killers is mainly responsible for the observed temperature dependence of the luminescence. Aside from the inhomogeneous broadening of the emission band, the extrinsic character of the luminescence is underlined by the experimental Stokes shift observed at 10 K. The analysis of the bandwidth and the vibrational progressions on the 4T1g(G) band is perfectly explained in terms of coupling to the a1g mode. The increase of the Huang-Rhys factor on passing from Na6MnCl8, S(a1g) = 5, to Na6MnBr8, S(a1g = 8, is reasonably explained through a microscopic model. It is demonstrated that the lifetime-temperature dependence is mainly governed by the overlap between the absorption and emission bands. This overlap is estimated subtracting the odd-phonon contribution to the Stokes shift since phonon assistance is not required for excitation transfer through superexchange. The existence of Mn2+-Mn2+ transfer down to 2 K is related to the perfect,cubic symmetry of these compounds, and to a small coupling to the Jahn-Teller e(g) mode. The different thermal shifts experienced by the luminescence and the excitation 4T1g(G) band are also discussed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> COUPLED MANGANESE(II) PAIRS; SUZUKI-PHASE; TEMPERATURE-DEPENDENCE; INFRARED LUMINESCENCE; LIFETIME MEASUREMENTS; ELPASOLITE LATTICES; EXCITATION-SPECTRA; OPTICAL-SPECTRA; CRYSTALS; ABSORPTION<\/p>\n<\/div><\/details><\/div>\n\n\n\n

POLARIZED OPTICAL-ABSORPTION SPECTROSCOPY OF THE Tl2<\/sub>MnF5<\/sub>-CENTER-DOT-H2<\/sub>O 1D MANGANESE(III) SINGLE-CRYSTAL<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, NUNEZ P, DELUCAS MCM<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF SOLID STATE CHEMISTRY     Volume:<\/strong> 110 Issue:<\/strong> 2  Pages<\/strong>: 370-383 <\/p>\n\n\n\n

Abstract:<\/strong> The polarized optical absorption spectra of the ID manganese (III) fluoride Tl2MnF5 . H2O are investigated in the 9.5 -300 K temperature range. Throughout the work, special emphasis is placed on the correlation between the different spectroscopic parameters and the structural and magnetic properties of the title compound. Three prominent, strongly polarized broadbands are observed at 11,700, 17,500, and 20,800 cm-1, which are assigned to the spin-allowed crystal field bands within the d4 electronic configuration of the Jahn-Teller elongated MnF63- complex (D4h). Both the polarization and the temperature dependence of the oscillator strengths indicate that these bands are electric-dipole-assisted by odd parity vibrations, whereas the spin-forbidden transitions are induced by a pairwise exchange mechanism. A salient feature of the present work is the observation of vibronic progressions to a1g modes of 525, 505, and 375 cm-1 in the low temperature spectra of the 5B1g –> 5A1g and 5B2g bands. The nature of these modes and the experimental Huang-Rhys factors are analyzed in terms of the linear electron-phonon coupling coefficients, which are derived by correlating the optical spectra of several fluorides with the local geometry around the Mn(III). The presence of an exciton magnon peak in the low temperature spectra is also noteworthy. The temperature dependence of the intensity of this peak as well as of the spin-forbidden transitions provides evidence of magnetic ordering below T(N) = 28 K and allows us to estimate an intrachain exchange constant of J = 11 cm-1. (C) 1994 Academic Press, Inc<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> D-D SPECTRUM; MAGNETIC-STRUCTURES; PHASE-TRANSITIONS; COMPOUND; MN-2+; FLUOROMANGANATES(III); MONOHYDRATE; IONS; CS<\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL-PROPERTIES OF THE MNCL6<\/sub>4-<\/sup> COMPLEX FORMED IN ABCl3<\/sub>Mn2+<\/sup> PSEUDOPEROVSKITE CRYSTALS – INFLUENCE OF THE CHEMICAL PRESSURE<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, GUDEL HU, FURER N<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE      Volume:<\/strong> 60 Issue:<\/strong> 1  Pages<\/strong>: 581-584  <\/p>\n\n\n\n

Abstract:<\/strong> This work reports the excitation and luminescence spectra of several ABCl3:Mn2+ crystals. The variations in the optical spectra along this series are explained by changes in the Mn-Cl distance, R, of the MnCl64- complex as a consequence of the chemical pressure. The lattice relaxation around Mn2+ and the R dependence of the Stokes shift are analysed in detail.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> COUPLED MANGANESE(II) PAIRS; SPECTRA; DEPENDENCE; PHOTOLUMINESCENCE; TRANSITION; NH4MNCL3<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1993<\/strong><\/p>\n\n\n\n

OPTICAL-PROPERTIES OF TMA2<\/sub>CdBr4<\/sub> AND TMA2<\/sub>MNBr4<\/sub><\/summary>
\n

Author(s):<\/strong> VALIENTE R, DELUCAS MCM, ESPESO JI, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> SOLID STATE COMMUNICATIONS      Volume:<\/strong> 86 Issue:<\/strong> 10  Pages<\/strong>: 663-666  <\/p>\n\n\n\n

Abstract:<\/strong> The optical properties of [(CH3)4N]2MBr4 (M = Cd and Mn) crystals are investigated. Both crystals are positive biaxial with the principal axes of the optic indicatrix n(alpha),n(beta) and n(gamma) along the a, b and c orthorhombic directions, respectively. The birefringence, optic angle and refractive indexes were measured at room temperature. The monoclinic domain structure observed below Pmcn –> P12(1)\/c1 phase transition temperature is also analyzed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> PHASE-TRANSITIONS<\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMINESCENCE PROPERTIES OF CU-2+<\/sup>-DOPED TMA2<\/sub>MnBr4<\/sub> CRYSTALS AND A SPECTROSCOPIC STUDY OF THE CUBr4<\/sub>2-<\/sup> COMPLEXES FORMED<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER      Volume:<\/strong> 5 Issue:<\/strong> 16  Pages<\/strong>: 2625-2642  <\/p>\n\n\n\n

Abstract:<\/strong> This work investigates the influence of Cu2+ impurities on the luminescence properties Of TMA2MnBr4:Cu2+ as well as the local structure and orientation of the CuBr42- complexes formed, by means of the excitation and luminescence spectra, lifetime measurements and polarized optical absorption spectroscopy in the 10-300 K temperature range. It is demonstrated that the presence of an intense Br –> Cu2+ charge transfer (CT) band at 555 nm strongly favours a direct energy transfer from Mn2+ to the non-luminescent Cu2+ impurities The influence of this energy transfer on the Mn2+ luminescence intensity, lifetime and bandshape is analysed as a function of the Cu2+ concentration. The results are compared with previous ones obtained in one-dimensional Cu2+-doped TMAMnCl3 and TMAMnBr3 crystals. Two x, y-polarized bands at 18 000 and 28 400 cm-1, and two z-polarized bands at 23 800 and 36 100 cm-1 are observed in the CT spectra Of TmA2MnBr4:Cu2+. Their transition energies as well as their polarization are explained in terms of D2d symmetry distortions of the CuBr42- tetrahedra. We also analyse the triplet structure observed in the first CT band which is associated with the tetrahedral 2T1 CT state, which is split by the effect of both the static D2d distortion and the large spin-orbit coupling of the Br- ligands. The absence of discontinuities in the evolution of the CuBr42- CT bands with temperature supports the finding that no structural phase transition occurs below 270 K in these crystals.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> YELLOW THERMOCHROMIC MODIFICATIONS; TETRAHEDRAL CUCL42 ANIONS; ELECTRON-PARAMAGNETIC-RES; ONE-DIMENSIONAL LATTICE; DISCRETE SQUARE-PLANAR; PHASE-TRANSITION; BIS(N-METHYLPHENETHYLAMMONIUM) TETRACHLOROCUPRATE(II); TETRAMETHYLAMMONIUM TETRABROMOMANGANATE; EMISSION DYNAMICS; ROOM-TEMPERATURE<\/p>\n<\/div><\/details><\/div>\n\n\n\n

PHOTOLUMINESCENCE OF RBCAF3<\/sub>Mn2+<\/sub> – THE INFLUENCE OF PHASE-TRANSITIONS<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER  Volume:<\/strong> 5 Issue:<\/strong> 9  Pages<\/strong>: 1437-1446   <\/p>\n\n\n\n

Abstract:<\/strong> Precise photoluminescence measurements on an RbCaF3:Mn2+ sample containing Only 400 ppm of Mn2+ have been carried out in the 10-300 K temperature range. The results are compared with those obtained in other fluoroperovskites doped with Mn2+. The analysis of the 6A1g(S) –> 4T1g(G) excitation peak at room temperature leads to a Mn2+-F- distance R = 213.3 pm which is close to that derived from the experimental isotropic superhyperfine constant, A(s). The plot of the first moment of the emission band, MI, against temperature reveals a slight but sensible change of slope at T = 193 K which is associated with the O(h)1 –> D4h18 structural phase transition of the host lattice. Furthermore, at T = 40 K, M1 undergoes an abrupt increase of approximately 100 cm-1. This fact supports the existence of another phase transition involving an increase DELTAR\/R congruent-to 0.2% upon cooling, and thus a Situation which is Similar to that detected in the structural phase transition of KMnF3 at T(c3) = 81.5 K. To our knowledge this is the first time that clear evidence of both phase transitions in RbCaF3 has been achieved through an optical probe. Finally the variation of the 4A1g(G), 4E(g)(G) peak, E3, along the fluoroperovskite series is analysed.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> PEROVSKITE FLUORIDES; MN-2+-F DISTANCE; OPTICAL-SPECTRUM; RBCDF3; MN2+; DEPENDENCE; LATTICES; CRYSTALS; RBMNF3; KMGF3<\/p>\n<\/div><\/details><\/div>\n\n\n\n

PHASE-TRANSITION TEMPERATURES AND THERMAL HYSTERESIS IN NH4<\/sub>CL1<\/sub>-XBRX (X-LESS-THAN-OR-EQUAL-TO-0.05) CRYSTALS DETERMINED THROUGH CHARGE-TRANSFER SPECTRA OF CU2+(<\/sup>II) CENTERS<\/summary>
\n

Author(s):<\/strong> BRENOSA AG<\/a>, RODRIGUEZ F<\/a>, MORENO M<\/a><\/p>\n\n\n\n

Source:<\/strong> SOLID STATE COMMUNICATIONS  Volume:<\/strong> 85 Issue:<\/strong> 2  Pages<\/strong>: 135-140 <\/p>\n\n\n\n

Abstract:<\/strong> <\/p>\n\n\n\n

he transition temperatures and the small hysteresis associated to the beta –> delta phase transition in NH4Cl1-xBrx crystals (x less-than-or-equal-to 0.05) have been measured through the temperature dependence of the e(u)(pi + sigma, Cl) –> a1g* (approximately 3z2 – r2) peak corresponding to the CuCl4(NH3)22- impurity centre used as probe.<\/p>\n\n\n\n

The hysteresis DELTAT = 0.2 +\/- 0.1 K obtained for NH4Cl compares well with the values derived from dilatometric and specific heat measurements but not with those coming from quasi elastic light scattering or ultrasonic data. The present results support the equivalence of P-T and X-T phase diagrams around of x = 0.<\/p>\n\n\n\n

<\/p>\n\n\n\n

Keywords:<\/strong> SINGLE-CRYSTALS; TRANSFER BANDS; HIGH-PRESSURE; NH4CL; ND4CL; COMPLEXES; EXPANSION<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1992<\/strong><\/p>\n\n\n\n

INFLUENCE OF PHASE-TRANSITIONS IN THE CHARGE-TRANSFER SPECTRA OF TMA2<\/sub>MNCL4<\/sub>CU2+<\/sup><\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> FERROELECTRICS    Volume:<\/strong> 125    Issue:<\/strong> 1-4    Pages:<\/strong> 159-164    <\/p>\n\n\n\n

Abstract:<\/strong> The local geometry and the orientation of the CuCl42- complexes formed in TMA2MnCl4:Cu2+ are studied through the polarized Charge Transfer (CT) spectra in the 10 – 300 K temperature range. The analysis of these spectra indicates that CuCl42-complexes display distortions of D2d symmetry along only one of the tetrahedron S4 axes, with bond angles of 124-degrees. The structural phase transitions undergone by this crystal mainly involve reorientational motions of the CuCl42- complexes. Below the P112(1)\/n–>P12(1)\/c1 phase transition temperature, 171 K, the CT spectra experience the highest variations due to the formation of domains.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> SINGLE-CRYSTALS; TETRAMETHYLAMMONIUM<\/p>\n\n\n\n

<\/p>\n\n\n\n

<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

STUDY OF PRECIPITATED PHASES IN MN-2+<\/sup> SINGLY DOPED KBr CRYSTALS BY OPTICAL SPECTROSCOPY AND EPR<\/summary>
\n

Author<\/strong>(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> PHYSICA STATUS SOLIDI B-BASIC RESEARCH    Volume:<\/strong> 172    Issue:<\/strong> 2    Pages:<\/strong> 719-731    <\/p>\n\n\n\n

Abstract:<\/strong> The aggregation states of Mn2+ in KBr:Mn2+ doped crystals are investigated using optical techniques. Excitation and luminescence spectra as well as lifetimes are obtained as a function of temperature of different crystals. It is demonstrated that at least three different Mn2+ precipitates are formed inside the KBr. Two of them contain MnBr64- units with slightly distorted octahedral symmetries, while the third one involves two non-equivalent tetrahedral MnBr42- units. These centers exhibit a broad green luminescence band.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> COUPLED MANGANESE(II) PAIRS; ENERGY-TRANSFER; SUZUKI-PHASE; MAGNETIC-PROPERTIES; ALKALI-HALIDES; TRANSITION; SPECTRA; NACL; ABSORPTION; EMISSION<\/p>\n\n\n\n

<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

STUDY OF PARTICLE FORM-FACTORS F(Q) WITH CUBIC SYMMETRY – INFLUENCE ON THE SANS INTENSITIES<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, SAL JCG, MORENO M<\/p>\n\n\n\n

Source:<\/strong> PHYSICA B    Volume:<\/strong> 180    Pages:<\/strong> 531-533    Part:<\/strong> Part A    <\/p>\n\n\n\n

Abstract:<\/strong> This work examines the way of extracting reliable information on the shape and size of microcrystalline precipitates with cubic morphologies from SANS experiments out of the Guinier region. The information can be derived from the I(q) dependences for different crystallographic directions as I is proportional to q(-n) and n is a function of both the q direction and the precipitate shape.<\/p>\n\n\n\n

<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1991<\/strong><\/p>\n\n\n\n

POLARIZED CHARGE-TRANSFER SPECTRA OF CU2+<\/sup> DOPED TMA2MNCL4 CRYSTALS– STUDY OF THE CUCL4<\/sub>2-<\/sup> JAHN-TELLER DISTORTION<\/summary>
\n

Author<\/strong>(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, ARAMBURU JA<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER    Volume:<\/strong> 3    Issue:<\/strong> 45    Pages:<\/strong> 8945-8957    <\/p>\n\n\n\n

Abstract:<\/strong> The charge transfer (c-r) spectra of the CUCl42- complex formed in TMA2MnCl4:Cu2+ single crystals are investigated in the 10-300 K temperature range. Two chi, gamma-polarized bands at 24 300 and 33 700 cm-1, and two z-polarized ones at 29 500 and 41 000 cm-1 are assigned to CT transitions of the CuCl42-. These transition energies, as well as the degree of polarization of the CT bands, are explained in terms of Jahn-Teller distortions of D2d symmetry. The ms-Xa calculations performed on this complex support this view. By means of these data, both the trans-Cl-Cu-Cl distortion angle and the orientation of CuCl4<\/sub>2-<\/sup> in the lattice are determined. The sensitivity of CT bands of CuCl4(2-) for detecting the structural phase transition sequence of this crystal is analysed as well. A noteworthy finding of this work concerns the profound changes experienced by CT bands below the monoclinic P112l\/n –> P12l\/c1 phase transition temperature at 171 K. The spectra become nearly isotropic as a consequence of the formation of structural domains. These results are compared with those obtained in pure chlorocuprates such as Cs2CuCl4 and TMA2<\/sub>CuCl4<\/sub>.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> ELECTRON-PARAMAGNETIC-RES; PHASE-TRANSITION; HYDROSTATIC-PRESSURE; SINGLE-CRYSTALS; TRANSFER BANDS; TETRACHLOROCUPRATE(II); COMPLEXES; (N(CH3)4)2MNCL4; PARAMETERS; FEATURES<\/p>\n<\/div><\/details><\/div>\n\n\n\n

EVIDENCE FOR ANOMALOUS RELAXATION OF THE CuCl4(NH3<\/sub>)2<\/sub>2-<\/sup>CENTER IN NH4<\/sub>Cl BELOW TC<\/summary>
\n

Author(s):<\/strong> BRENOSA AG, MORENO M, RODRIGUEZ F, COUZI M<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 44    Issue:<\/strong> 18    Pages:<\/strong> 9859-9863    <\/p>\n\n\n\n

Abstract:<\/strong> The temperature dependence of the (a) e(u) (pi + sigma, Cl) –> a1g* (approximately 3z2-r2) charge-transfer transition, nu-CT; (b) e(g)* –> a1g* crystal-field transition, VCF; (C) Cu-NH3 and Cu-Cl A1g stretching mode frequencies (termed as nu-1 and nu-2, respectively) corresponding to the Cu-Cl4(NH3)2(2-) center in NH4Cl have been measured in the 100-300-K range. Below T(c), nu-CF and especially nu-CT undergo a red shift ascribed to the increase of the Cu2+-Cl- equatorial distance, R(eq), of the center although the lattice parameter a decreases. This anomalous relaxation is strongly supported by Raman data, giving variations DELTA-nu-1 = 7 +\/- 1 cm-1 and DELTA-nu-2 = 11 +\/- 3 cm-1 in the 243-213-K range. Based on these data, the variations undergone by R(eq) and the axial Cu+-NH3 distance R(ax) in such a temperature range are estimated to be DELTA-R(eq) congruent-to + 2.0 +\/- 0.6 pm, DELTA-R(ax) congruent-to -0.40 +\/- 0.05 pm. The present results emphasize the usefulness of standard spectroscopic tools for detecting this unusual local relaxation which lies beyond the resolution limit of the extended x-ray-absorption fine-structure technique. To our knowledge this is the first time that evidence of such a phenomenon is reported.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> CHARGE-TRANSFER TRANSITIONS; TEMPERATURE-DEPENDENCE; THERMAL-EXPANSION; OPTICAL-SPECTRUM; FINE-STRUCTURE; CUCL42; ABSORPTION; COMPLEXES; DISTANCE; CRYSTALS<\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMINESCENCE PROPERTIES OF MN-2+<\/sup> IN KMGF3<\/sub> AND KZnF3<\/sub> PEROVSKITE CRYSTALS – EVIDENCE OF A DYNAMIC JAHN-TELLER EFFECT<\/summary>
\n

Author<\/strong>(s):<\/strong> RODRIGUEZ F, RIESEN H, GUDEL HU<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 50    Issue:<\/strong> 2    Pages:<\/strong> 101-110   <\/p>\n\n\n\n

Abstract:<\/strong> The luminescence spectra of KZnF3: Mn2+ and KMgF3: Mn2+ are presented and analysed. At T = 5 K, both spectra consist of one zero phonon line from which a phonon sideband centered at about 600 nm is formed. The existence of the dynamical Jahn-Teller (JT) effect in the first 4T1g excited state is evidenced through a reduction of the spin-orbit splitting displayed by the zero phonon lines. JT energies of 530 and 450 cm-1 associated with electron-phonon couplings carrying e(g) type distortions around Mn2+ are estimated for KZnF3: Mn2+ and KMgF3: Mn2+, respectively. Vibronic sidebands are interpreted in terms of lattice modes rather than local vibrations of the MnF6(4-) complex. The magnetic and electric dipole character of the 4T1g –> 6A1g transition is analysed by the temperature dependence of the luminescence spectra and their lifetimes.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> TRANSITION-METAL IONS; HIGH-RESOLUTION MCD; TEMPERATURE-DEPENDENCE; EXCITATION-SPECTRA; OPTICAL-SPECTRUM; FLUORIDE; STATE; RBMNF3; MGF2; MN2+<\/p>\n\n\n\n

Reprint Address:<\/strong> RODRIGUEZ, F (reprint author), UNIV CANTABRIA, SECC CIENCIA MAT, DCITT &<\/p>\n<\/div><\/details><\/div>\n\n\n\n

DETERMINATION OF THE SHAPE AND SIZE OF AGGREGATED PHASES IN NaCl-MN2+<\/sup> BY SMALL-ANGLE NEUTRON-SCATTERING<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, SAL JCG, MORENO M, DEGEYER A, JANOT C<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 43    Issue:<\/strong> 10    Pages:<\/strong> 7519-7526    Part:<\/strong> Part A    <\/p>\n\n\n\n

Abstract:<\/strong> Suzuki-phase precipitates formed in NaCl:Mn2+ have been studied by small-angle neutron scattering. The experiments, carried out on single crystals of NaCl with different Mn2+ concentrations, indicate the usefulness of this technique for detecting precipitates and for determining their shape and size. A salient feature of the present work is the anisotropic character of the neutron-scattering intensity, which provides a way for determining the size of the percipitate out of the Guinier region. The analysis of the intensity decay allows us to detect precipitate shapes displaying slight modifications with respect to the perfect cube.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> SUZUKI-PHASE; DOPED NACL; CRYSTALS; SPECTROSCOPY<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1990<\/strong><\/p>\n\n\n\n

PHASE-TRANSITIONS IN NH4<\/sub>CL1-XBRX STUDIED BY CHARGE-TRANSFER BANDS OF CU-2+<\/sup> IMPURITIES<\/summary>
\n

Author<\/strong>(s):<\/strong> BRENOSA AG, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> FERROELECTRICS    Volume:<\/strong> 106    Pages:<\/strong> 187-192<\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMINESCENCE OF THE NEW ELPASOLITE Rb2<\/sub>KGaF6<\/sub> DOPED WITH Cr3+<\/sup><\/summary>
\n

Author(s):<\/strong> DELUCAS CM, RODRIGUEZ F, DANCE JM, MORENO M, TRESSAUD A<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF LUMINESCENCE    Volume:<\/strong> 48-9    Pages:<\/strong> 553-557    Part:<\/strong> Part 2   <\/p>\n\n\n\n

Abstract:<\/strong> Photoluminescence, lifetime, optical absorption and EPR measurements on Rb2KGaF6:Cr3+ have been carried out in the 10-300 K temperature range. The emission spectrum at 10 K shows a very rich vibrational structure which can be mainly explained through the vibrational modes of the CrF6(3-) complex. Comparison of the experimental vibrational frequencies and zero-phonon line with those for K2NaAlF6:Cr3+ indicates that the Cr3+-F- distance is about 1.5 pm larger for Rb2KGaF6:Cr3+. The present data clearly demonstrate the existence of a first order phase transition at 129 K (upon cooling) with an involved hysteresis DELTA-T = 6 K although the local geometry around Cr3+ in the noncubic phase remains essentially octahedral.<\/p>\n\n\n\n

KeyWords<\/strong> Plus:<\/strong> STRUCTURAL PHASE-TRANSITIONS; D-D SPECTRUM; RB2KMIIIF6 ELPASOLITES; OPTICAL-SPECTRUM; K2NAGAF6-CR3+; SPECTROSCOPY; DEPENDENCE; MN-2+; CR3+<\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL INVESTIGATIONS ON (N(CH3<\/sub>)4<\/sub>)2<\/sub>MnCl4<\/sub> – A NEW PHASE-TRANSITION AT 90-K<\/summary>
\n

Author<\/strong>(s):<\/strong> DELUCAS MCM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> FERROELECTRICS    Volume:<\/strong> 109    Pages:<\/strong> 21-26<\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL AND EPR STUDY OF PRECIPITATED PHASES IN NaBr-Mn2+<\/sup><\/summary>
\n

Author<\/strong>(s):<\/strong> DELUCAS CM, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Abstract. <\/strong>As-grown NaBr : Mn\u00bb crystals have been investigated using photostimulated luminescence, EPR and optical absorption techniques in the 6 <\/em>K-300 K temperature range. Through them the formation of a precipitated phase involving Mn2+, whose magnetic phase transition temperature is well below 6 K, is established. This conclusion then supports the presence of the Suzuki phase previously inferred from Raman data. The value Q* <\/strong>(Alg) = 130 t 7 <\/em><\/strong>cm-‘ derived at 14 K from the vibrational progression in the 4T,(G) band  concurs with thecorresponding Ramanvalue. It isshown that, only through the 4Al(G),’E (G) peak, lying at 419.6 nm at 14 K for the present case, the presence of MnBri- cannot be definitely established. This situation is however improved by looking at the Stokes  shifts, the 10 Dq<\/em>values and also the optical bandwidths. The analysis of 10 Dq<\/em>and O(<\/strong>A,,) <\/strong>suggests that the Mnzt-Br- distance R is higher than that for MnBr,or Cdox sMn, IsBrzH. owever an increase AR = 4.8 pm with respect to MnBr, does not fully account for the ‘anomalous’ ‘A,(G), 4E(G) peak position in the present case where a value J <\/em><\/strong>= 0.014 cm-‘ has been derived for the exchange constant from the EPR bandwidth AHpp = 117 G. Attention has been paid to the influence of temperature changes on the optical peak positions  as well as to the effects of a quenching at 600 \u00abC. Although AHpp becomes 2.5 times higher, no evidence is obtained on the formation of isolated Mn2- ions after quenching.<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER    Volume:<\/strong> 2    Issue:<\/strong> 7    Pages:<\/strong> 1891-1903   <\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMINESCENCE LIFETIME MEASUREMENTS FROM SPECTROFLUORIMETERS EMPLOYING LOW-COST ANALOG INPUT INTERFACES<\/summary>
\n

Author<\/strong>(s):<\/strong> DELUCAS CM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> REVIEW OF SCIENTIFIC INSTRUMENTS    Volume:<\/strong> 61    Issue:<\/strong> 1    Pages:<\/strong> 23-26    Part:<\/strong> Part 1 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1989<\/strong><\/p>\n\n\n\n

EVIDENCE OF A NEW 1ST-ORDER PHASE-TRANSITION AT 92-K IN ((CH3<\/sub>)4<\/sub>N)2<\/sub>MnCl4<\/sub> SINGLE-CRYSTALS<\/summary>
\n

Author(s):<\/strong> DELUCAS MCM, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS-CONDENSED MATTER    Volume:<\/strong> 1    Issue:<\/strong> 26    Pages:<\/strong> 4251-4256<\/p>\n<\/div><\/details><\/div>\n\n\n\n

EVIDENCE OF SUZUKI PHASE AGGREGATES IN NaCl-MN<\/sub>2+<\/sup>, BY MEANS OF SMALL-ANGLE SCATTERING<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M, SAL JCG, JANOT C<\/p>\n\n\n\n

Source:<\/strong> PHYSICA B    Volume:<\/strong> 156    Pages:<\/strong> 33-35<\/p>\n<\/div><\/details><\/div>\n\n\n\n

TEMPERATURE-DEPENDENCE OF CRYSTAL-FIELD PEAKS OF RbMnF3<\/sub> AND KMnF3<\/sub><\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M, DANCE JM, TRESSAUD A<\/p>\n\n\n\n

Source:<\/strong> SOLID STATE COMMUNICATIONS    Volume:<\/strong> 69    Issue:<\/strong> 1    Pages:<\/strong> 67-71    <\/p>\n\n\n\n

Abstract:<\/strong> <\/strong>The influence of temperature on the position of crystal-field peaks of RbMnF3<\/sub> and KMnF3<\/sub> has been investigated in the 14\u2013550 K range. Upon warming in the 200\u2013550 K range, the 4<\/sup>T<\/em>1g<\/em><\/sub>(G<\/em>) peak dependent on 10 Dq<\/em> experiences a total blue shift of 470 cm-1<\/sup>. It is shown that only 40% of this shift arises from thermal expansion effects, the rest being due to the explicit (\u2202E<\/em>\/\u2202T<\/em>)v<\/sub><\/em> term. The positive sign of this term is associated to higher vibration frequencies for the 4<\/sup>T<\/em>1g<\/em><\/sub>(G<\/em>) state (belonging mainly to the t<\/em>4<\/sup>e<\/em> configuration) than for 6<\/sup>A<\/em>1g<\/em><\/sub>(S<\/em>) as a result of smaller Mn2+<\/sup>-F–<\/sup> distances for that excited state. Below 200 K the present data reflect the existence of magnetic and structural (only for KMnF3<\/sub>) phase transitions in the compounds.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1988<\/strong><\/p>\n\n\n\n

MAGNETIC-PROPERTIES OF PRECIPITATED PHASES IN MN2+<\/sup> DOPED ALKALI-HALIDES<\/summary>
\n

Author<\/strong>(s):<\/strong> MORENO M, RODRIGUEZ F, SAL JCG<\/p>\n\n\n\n

Source:<\/strong> JOURNAL DE PHYSIQUE    Volume:<\/strong> 49    Issue:<\/strong> C-8    Pages:<\/strong> 1811-1812    Part:<\/strong> Part 3   <\/p>\n<\/div><\/details><\/div>\n\n\n\n

A STUDY OF PHASE-TRANSITIONS IN NH4<\/sub>Br USING CHARGE-TRANSFER BANDS OF CU2+<\/sup> CENTERS AS PROBES<\/summary>
\n

Author<\/strong>(s):<\/strong> BRENOSA AG, RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Abstract. <\/strong>Charge transfer(cr)spectradue tosmallamounts(-lOO ppm)~f[CuBr,(NH,)~]\u2019 centres in the NH,Br lattice have been investigated in the 300-14 K temperature range. When upon cooling the y+ 6 <\/em>phase transition occurs the  assigned e,(n + U; <\/em>Br)-+ a;, and e,(u + R; <\/em><\/strong>Br)- aC peaks experience abrupt red shifts of 700 <\/em><\/strong>and 1200 cm-\u2019 respectively. stressing the great sensitivity of CT <\/em>peaks for detecting that transition. Those red shifts support the assertion that when the y -+ b <\/em>transition is produced the Cu*\u2019-Br- distance increases though the average lattice parameter of NH,Br decreases abruptly by 2.4 pm. This is the first time that the first-order sluggish y+ 6 <\/em>transition in NH,Br and the hysteresis effects involved have been clearly detected using an impurity as probe. Moreover CT bands also detect the phase transition at 234 K and the possibility for the crystal to remain in a metastable tetragonal phase below 78 K.<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS C-SOLID STATE PHYSICS    Volume:<\/strong> 21    Issue:<\/strong> 17    Pages:<\/strong> L623-L630    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

MAGNETIC-SUSCEPTIBILITY OF THE SUZUKI PHASE FORMED IN NaCl-MN2+<\/sup> IN THE 0.07-4.2-K TEMPERATURE-RANGE<\/summary>
\n

Author(s):<\/strong> SAL JCG, RODRIGUEZ F, MORENO M, THOLENCE JL<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 37    Issue:<\/strong> 1    Pages:<\/strong> 454-458    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1987<\/strong><\/p>\n\n\n\n

LOW-TEMPERATURE SPECIFIC-HEAT MEASUREMENTS FOR THE SUZUKI PHASE IN NaCl-Mn2+<\/sup> – EVIDENCE OF A MAGNETIC TRANSITION<\/summary>
\n

Author(s):<\/strong> GOMEZSAL JC, MORENO M, RODRIGUEZ F, REVEX A, THOLENCE JL<\/p>\n\n\n\n

Abstract. <\/strong>Specific heat measurements for an as-grown NaCl: Mn2+ crystal (Mn2′ <\/strong>concentration: 17000 ppm) containing the Suzuki phase have been carried out in the 0.1-10 K temperature range. The contribution due to the Suzuki phase shows a very sharp peak at 0.2 K which strongly supports the existence of an antiferromagnetic phase transition. The experimental entropy change associated with such a peak, equal to 16.6 J K-‘ mol-‘, is very  close to the molar magnetic entropy expected when S <\/em><\/strong>= B <\/strong>ions are involved. To our knowledge this is the first time that relevant specific heat data on precipitated phases in insulator materials have been reported.<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS C-SOLID STATE PHYSICS    Volume:<\/strong> 20    Issue:<\/strong> 19    Pages:<\/strong> L421-L424<\/p>\n<\/div><\/details><\/div>\n\n\n\n

STUDY OF AS GROWN RbCl-Mn2+<\/sup> BY MEANS OF PHOTOLUMINESCENCE AND ELECTRON-PARAMAGNETIC-RES<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M, ROUSSEAU JJ<\/p>\n\n\n\n

Source:<\/strong> CRYSTAL LATTICE DEFECTS AND AMORPHOUS MATERIALS    Volume:<\/strong> 16    Issue:<\/strong> 1-4    Pages:<\/strong> 161-167 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

MN-2+<\/sup> IN CUBIC PEROVSKITES – DETERMINATION OF THE Mn2+<\/sup>-F- DISTANCE FROM THE OPTICAL-SPECTRUM<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M, TRESSAUD A, CHAMINADE JP<\/p>\n\n\n\n

Source:<\/strong> CRYSTAL LATTICE DEFECTS AND AMORPHOUS MATERIALS    Volume:<\/strong> 16    Issue:<\/strong> 1-4    Pages:<\/strong> 221-225 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL AND RAMAN INVESTIGATION OF NH4<\/sub>Cl-Cu2+<\/sup><\/summary>
\n

Author<\/strong>(s):<\/strong> RODRIGUEZ F, BRENOSA AG, ARAMBURU JA, MORENO M, CALLEJA JM<\/p>\n\n\n\n

Abstract. <\/strong>We have explored the centre I1 <\/strong>formed in NH,CI: Cu2+ crystals by means of optical absorption and Raman spectroscopy. The crystal-field spectrum of centre I1 <\/strong>is shown to be composed of three bands, consistent with its Ddh<\/strong>symmetry. An analysis of peak positions suggests NHrCu2+ and CI–Cu2+ distances close to 1.9 <\/strong>and 2.4 A<\/strong>respectively. At 14 K the crystal-field bands assigned as <\/strong>b&y) + aI8 and e,(xz; yz<\/em>) <\/em>+ a,, show nice vibronic progressions corresponding to P <\/strong>= 400 <\/strong>* 15 <\/strong>cm-I. Raman spectroscopy reveals the presence of a sharp peak corresponding to S2, <\/em><\/strong>= 445 <\/strong>cm-‘. Both P <\/strong>and Q, <\/strong>frequencies are associated with the NHTCu2+ symmetric stretching of the (CUCI,(NH,),]~- unit. This difference reflects higher NHrCu2+ distances for the excited states due to the promotion of an additional electron to the strongly anti-bonding alg level.<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS C-SOLID STATE PHYSICS    Volume:<\/strong> 20    Issue:<\/strong> 26    Pages:<\/strong> L641-L647  <\/p>\n<\/div><\/details><\/div>\n\n\n\n

CHARGE-TRANSFER BANDS OF NH4<\/sub>Cl-Cu2+<\/sup> – INFLUENCE OF THE PHASE-TRANSITION<\/summary>
\n

Author<\/strong>(s):<\/strong> BRENOSA AG, MORENO M, RODRIGUEZ F<\/p>\n\n\n\n

Source:<\/strong> SOLID STATE COMMUNICATIONS    Volume:<\/strong> 63    Issue:<\/strong> 6    Pages:<\/strong> 543-547 <\/p>\n<\/div><\/details><\/div>\n\n\n\n

LOW-TEMPERATURE BEHAVIOR OF THE PHASE FORMED IN NaCl-Mn<\/summary>
\n

Author(s):<\/strong> GOMEZSAL JC, THOLENCE JL, RODRIGUEZ F, RAVEX A, MORENO M, ARAMBURU JA<\/p>\n\n\n\n

Source:<\/strong> CRYSTAL LATTICE DEFECTS AND AMORPHOUS MATERIALS    Volume:<\/strong> 16    Issue:<\/strong> 1-4    Pages:<\/strong> 235-239   <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1986<\/strong><\/p>\n\n\n\n

THERMAL-EXPANSION AROUND AN IMPURITY – STUDY OF KZnF3<\/sub>-Mn2+<\/sup><\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Abstract. <\/strong>The thermal expansion of the Mn*’-F- bond in KZnF3 : Mn2+ in the 15-300 K temperature range has been studied from the variations undergone by the crystal-field spectrum. It is shown that the thermal expansion effects are clearly more significant for the Mn2+-F- distance than for the Zn2′-F- distance of the perfect lattice. In this way the linear thermal expansion coefficient (Y for Mn*+-F- is found to be (Y = (38 k 14)10-6 K-‘ at room temperature to be compared with (Y = (15 * 0.7)10-6 K-I for the host lattice. To our knowledge this is <\/strong>the first time that data on thermal expansion effects around an impurity have been reported<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF PHYSICS C-SOLID STATE PHYSICS    Volume:<\/strong> 19    Issue:<\/strong> 23    Pages:<\/strong> L513-L517    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

FORMATION OF PRECIPITATES IN DOPED IONIC-CRYSTALS – EVIDENCE THROUGH THE LUMINESCENCE<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> SOLID STATE COMMUNICATIONS    Volume:<\/strong> 58    Issue:<\/strong> 10    Pages:<\/strong> 701-704   <\/p>\n\n\n\n

Abstract: <\/strong>It is stressed in this work that for ionic crystals doped with luminescent cations the progressive red shift of the emission peak energy when temperature increases is a direct<\/em> proof of the formation of microcrystalline precipitated phases inside the host lattice. As an example the case of as grown RbCl:Mn2<\/sup>+<\/sup> crystals is reported and analyzed in detail.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

DEPENDENCE OF THE OPTICAL-SPECTRUM OF MnF6<\/sub>4-<\/sup> ON THRE Mn2+<\/sup>-F-DISTANCE<\/summary>
\n

Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL PHYSICS    Volume:<\/strong> 84    Issue:<\/strong> 2    Pages:<\/strong> 692-697    <\/p>\n\n\n\n

Abstract<\/strong>: Wehave measured by means of photoluminescence the energy of crystal-fieldpeaks for RbCdF3<\/sub>: Mn2+<\/sup> and KZnF3<\/sub>: Mn2+<\/sup> where the valueof the Mn2+<\/sup>\u2013F\u2212<\/sup> distance, R<\/em>, derived by EXAFS is R<\/em>=2.13\u00b10.01\u00c5 and R<\/em>=2.08\u00b10.01 \u00c5, respectively. From these data and thosefor RbMnF3<\/sub> and KMnF3<\/sub> we have studied the dependence onR<\/em> of the B<\/em>, C<\/em>, and 10 Dq parameters forthe MnF6<\/sub>4-<\/sup> complex. This analysis reveals that within the experimentalerrors, B<\/em> and C<\/em> are constant in the range 2.07<R<\/em><2.14\u00c5, in agreement with recent self-consistent calculations for MnF6<\/sub>4-<\/sup>, whichalso predict that 10 Dq=KR<\/em>\u2212n<\/em><\/sup>, where K<\/em> and n<\/em> areconstant. The present study confirms this dependence, n<\/em> being 4.4which is also in accord to the theoretical predictions. Thebest values of R<\/em> derived from optical spectra are foundto be R<\/em>=2.141\u00b10.004 \u00c5 (for RbCdF3<\/sub>: Mn2+<\/sup>) and R<\/em>=2.075\u00b10.004 \u00c5(for KZnF3<\/sub>: Mn2+<\/sup>). The present analysis also points out thatby measuring the changes induced on the optical spectrum ofMnF6<\/sub>4-  in<\/sup> a given lattice we can detect changes inthe Mn2+<\/sup>\u2013F\u2212<\/sup> distance down to 10\u22123<\/sup> \u00c5. In this waywe have derived the difference, \"Delta\"R<\/em>, between R<\/em> at roomtemperature and at 77 K for KZnF3<\/sub>: Mn2+<\/sup>. The obtainedvalue \"Delta\"R<\/em>=(9\u00b11)10\u22123<\/sup> \u00c5 is in agreement with the one \"Delta\"R<\/em>=(10\u00b13.5)10\u22123 <\/sup>\u00c5 derived previously from the variations undergone by the isotropicsuperhyperfine constant As<\/sub><\/em>. Finally the present results are compared tothose for some complexes of Eu2+<\/sup>, Co2+<\/sup>, Ni2+<\/sup>, and Cr3+<\/sup>. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

1985<\/strong><\/p>\n\n\n\n

FeCl3<\/sub> SOLUTIONS IN ISOPROPANOL-WATER<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> TRANSITION METAL CHEMISTRY    Volume:<\/strong> 10    Issue:<\/strong> 3    Pages:<\/strong> 108-112    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

CHARACTERIZATION OF FeCl4<\/sub>– AND FeBr4<\/sub>– IN SOLUTION BY MEANS OF ELECTRON-PARAMAGNETIC-RES<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> TRANSITION METAL CHEMISTRY    Volume:<\/strong> 10    Issue:<\/strong> 9    Pages:<\/strong> 351-353<\/p>\n<\/div><\/details><\/div>\n\n\n\n

AS GROWN LiF-Mn2+<\/sup> SAMPLES ANALYZED BY LUMINESCENCE<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

<\/p>\n\n\n\n

Source:<\/strong> JOURNAL DE PHYSIQUE    Volume:<\/strong> 46    Issue:<\/strong> C-7    Pages:<\/strong> 151-153    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

LUMLUMINESCENCE OF MnF2<\/sub> SAMPLES CONTAINING OXYGEN<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M, BARUCHEL J, HENRY JY<\/p>\n\n\n\n

Source:<\/strong> JOURNAL DE PHYSIQUE    Volume:<\/strong> 46    Issue:<\/strong> C-7    Pages:<\/strong> 155-157  <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1984<\/strong><\/p>\n\n\n\n

MAGNETIZATION MEASUREMENTS ON IRON (III) SOLUTIONS FOR DETECTING OLIGOMER FORMATION<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M, SAL JCG<\/p>\n\n\n\n

Abstract:<\/strong><\/p>\n\n\n\n

Source:<\/strong> ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES    Volume:<\/strong> 39    Issue:<\/strong> 7    Pages:<\/strong> 617-622    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

1983<\/strong><\/p>\n\n\n\n

THE INFLUENCE OF WATER ADDITION ON SOLUTIONS OF FeCl3<\/sub> IN ISOPROPANOL<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/a>, FAYET JC, VARRET F<\/p>\n\n\n\n

Source:<\/strong> ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES    Volume:<\/strong> 38    Issue:<\/strong> 6    Pages:<\/strong> 701-702    <\/p>\n<\/div><\/details><\/div>\n\n\n\n

DOUBLE EXCITATION TRANSITIONS IN MN2+<\/sup>-DOPED ALKALI-HALIDES<\/summary>
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Author<\/strong>(s):<\/strong> MORENO M, RODRIGUEZ F, ARAMBURU JA, JAQUE F, LOPEZ FJ<\/p>\n\n\n\n

Source:<\/strong> PHYSICAL REVIEW B    Volume:<\/strong> 28    Issue:<\/strong> 10    Pages:<\/strong> 6100-6103    <\/p>\n\n\n\n

Abstract<\/strong>: It is shown in this work that the room-temperature excitation spectra of as-grown crystals of LiF, NaF, NaCl, KCl, and KBr doped with Mn2+<\/sup> reveal the existence of double excitation peaks. These peaks are related to the formation of precipitated phases containing Mn2+<\/sup> in the alkali halide lattice. In the case of LiF:Mn2<\/sup>+<\/sup> the position of the [4<\/sup>A<\/em>1<\/sub>(G<\/em>), 4<\/sup>E<\/em>(G<\/em>)] and 4<\/sup>T<\/em>1<\/sub>(G<\/em>) peaks suggests an anomalously small Mn2+<\/sup>– F–<\/sup> distance for the precipitated phase.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

MAGNETIC-SUSCEPTIBILITY MEASUREMENTS ON A FROZEN SOLUTION OF FeCl4-<\/sup> ANIONS IN ISOPROPANOL IN THE 0.07-K-4.2-K TEMPERATURE-RANGE<\/summary>
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Author(s):<\/strong> <\/strong>RODRIGUEZ F, MORENO M, GOMEZSAL JC, THOLENCE JL<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL PHYSICS    Volume:<\/strong> 78    Issue:<\/strong> 10    Pages:<\/strong> 6247-6251     <\/p>\n\n\n\n

Abstract<\/strong>: Magneticsusceptibility measurements in the range 0.07\u20134.2 K have been performedon a 0.32 M solution of [FeCl4<\/sub>]\u2212<\/sup> anions in isopropanol.At 0.1 K the experimental susceptibility is more than anorder of magnitude smaller than that corresponding to a single[FeCl4<\/sub>]\u2212<\/sup> monomer, a fact which clearly suggests the formation ofdimers of [FeCl4<\/sub>]\u2212<\/sup> with antiferromagnetic coupling. A careful analysis ofthe susceptibility curve has been performed allowing the existence ofdimers as well as of monomers in the solution. Moreover,zero-field splitting terms of the form D<\/em>[s<\/em>\u22121\/3 s<\/em>(s<\/em>+1)] have alsobeen introduced in the theoretical description of both monomers anddimers. The experimental susceptibility can be satisfactorily explained along theselines and is consistent with the following conclusions: (1) Around90% of the [FeCl4<\/sub>]\u2212<\/sup> units present in the solution arein dimer form while the remainder are present as monomers;(2) The effective exchange interaction between the two ferric ionsinvolved in a dimer is J<\/em>=(0.15\u00b10.02) cm\u22121<\/sup>. This value isconsistent with a Fe\u2013Cl\u2013S\u2013Cl\u2013Fe superexchange path where S<\/em> could bea solvent molecule; and (3) The [FeCl4<\/sub>]\u2212<\/sup> units do notdisplay a right Td<\/sub><\/em> symmetry but they are distorted bythe interaction with the solvent giving rise to a valueD<\/em>=\u2212(0.60\u00b10.10) cm\u22121<\/sup>. The present results point out that magnetic susceptibilitymeasurements in that range of temperature can provide us withuseful and detailed information on the solute\u2013solute and solute\u2013solvent interactionsin liquid solutions involving a paramagnetic complex. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.<\/p>\n<\/div><\/details><\/div>\n\n\n\n

OPTICAL SPECTROSCOPY OF MN2+<\/sup> IONS IN SOLID-SOLUTION AND SUZUKI PHASE IN NACL SINGLE-CRYSTALS<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M, JAQUE F<\/a>, LOPEZ FJ<\/p>\n\n\n\n

Source:<\/strong> JOURNAL OF CHEMICAL PHYSICS    Volume:<\/strong> 78    Issue:<\/strong> 1    Pages:<\/strong> 73-78    <\/p>\n\n\n\n

Abstract<\/strong>: Theoptical spectroscopy of Mn2+<\/sup> ions both in dipolar form andforming Suzuki-phase precipitates has been studied in NaCl by photostimulatedluminescence at room and liquid nitrogen temperatures. An analysis ofthe positions of the crystal field transitions shows that the10 Dq value is slightly higher (about 7%) in theSuzuki than in the dipolar phase while the covalency isthe same in both cases. Such analysis allows us toestimate the value f<\/em>\u2212f<\/em>=4.8% from the optical data which isin agreement with the EPR data for [MnCl6<\/sub>]4\u2212<\/sup> clusters. Moreover,an intense band peaking at 231 nm which disappears whenthe dipolar phase is formed has been ascertained to beassociated with the Suzuki phase. This band has been assignedto the double excitation 6<\/sup>A<\/em>1<\/sub>(S<\/em>) +6<\/sup>A<\/em>1<\/sub>(S<\/em>) \"--\u00bb width=\u00bb27″ height=\u00bb9″>4<\/sup>T<\/em>1<\/sub>(G<\/em>)+[4<\/sup>A<\/em>1<\/sub>(G<\/em>), 4<\/sup>E<\/em>(G<\/em>)]; that is consistent withthe existence of Mn2+<\/sup> ions in close positions in theSuzuki phase. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.<\/p>\n\n\n\n

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<\/p>\n\n\n\n

1980<\/strong><\/p>\n\n\n\n

THE INHIBITOR AGENT IN SUBRAMANIAN DISLOCATION ETCHANT FOR KCl<\/summary>
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Author(s):<\/strong> RODRIGUEZ F, MORENO M<\/p>\n\n\n\n

Source:<\/strong> ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCESJOURNAL OF CHEMICAL PHYSICS   Volume:<\/strong> <\/strong>35    Issue:<\/strong> <\/strong>12    Pages:<\/strong> <\/strong>1419-1420  <\/strong><\/p>\n<\/div><\/details><\/div>\n\n\n\n

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