Rafael Valiente - Academia.edu (original) (raw)

Papers by Rafael Valiente

Journal of Alloys and Compounds

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Wide band-gap semiconductors doped with transition-metal ions have attracted a lot of attention i... more Wide band-gap semiconductors doped with transition-metal ions have attracted a lot of attention in the past few years. Here we focus on the spectroscopic properties of Co 2+-doped ZnO in different structural conformations such as single crystal, thin film, nanorods and nanoparticles under different P −T conditions. Optical measurements were obtained by means of Raman and time-resolved spectroscopy using high-pressure techniques. Our main goal is to investigate the pressure-induced Wurtzite-to-Rock-Salt phase transition and how the structural conformation affects the Raman spectra as well as the absorption and emission spectra associated with Co 2+-doped ZnO. The effects of quantum confinement (dimensionality) are also investigated through the distinct spectral features observed in the samples as SC, TF, NW and NP helping us to clarify the still-unassigned absorption and emission spectra in terms of electron-phonon couplings and exchange interactions.

RSC Adv., 2014

The temperature-dependent green luminescence of Y3Ga5O12 nano-garnets doped with different concen... more The temperature-dependent green luminescence of Y3Ga5O12 nano-garnets doped with different concentrations of Er3+ ions has been measured from 300 to 850 K and, in more detail, in the biological range from 292 to 335 K.

Solid State Communications, 1993

The optical properties of [(CH3)4N12MBr4 (M = Cd and Mn) crystals are investigated. Both crystals... more The optical properties of [(CH3)4N12MBr4 (M = Cd and Mn) crystals are investigated. Both crystals are positive biaxial with the principal axes of the optic indicatrix n,,np and n, 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,/cl phase transition temperature is also analyzed.

Journal of Physics: Condensed Matter, 1995

The charge-transfer electronic structure of CuBr42- in (N(CH3)4)2CdBr4 crystals is investigated t... more 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 D2d symmetry of the CuBr42- complex. Some bands are split in the low-temperature spectra by the spin-orbit 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, CuBr42- experiences reorientational motions upon varying the temperature which are correlated with the temperature dependence of the monoclinic beta parameter below the Pmcn to P21c/ phase transition temperature Tcl=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 Tc2=20 K with a thermal hysteresis Delta T=10 K. This new phase transition, which had not previously been detected in the ((CH3)4N)2MBr4 (M=Zn, Mn, Co or Cd) series, would correspond to the monoclinic P21c/ to orthorhombic P212121 transition, confirming the predictions of the universal p-T phase diagrams of the title compounds.

Journal of Alloys and Compounds

Journal of Physics: Conference Series, 2020

The effects of pressure in electronic and vibrational properties of the double perovskite CaCu3Ti... more 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 I m 3 ¯ 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 I m 3 ¯ 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 highligh...

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Cancers, 2021

Head and Neck Cancer (HNC) is the seventh most common cancer worldwide with a 5-year survival fro... more 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 bi...

Journal of Physics: Condensed Matter, 2004

This work investigates the magnetic structure of Rb 2 CuCl 4 as a function of pressure and temper... more This work investigates the magnetic structure of Rb 2 CuCl 4 as a function of pressure and temperature using neutron diffraction. As in most A 2 CuCl 4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn-Teller (JT) antiferrodistortive structure of the CuCl 6 units. Rb 2 CuCl 4 undergoes a 3D magnetic transition at T N = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases T N , as ∂ T N /∂ P = 0.13 K kbar −1. This behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [C n H 2n+1 NH 3 ] 2 CuCl 4 (n = 1-3) and BMnF 4 (B = Li, Na, K, Rb, Tl, Cs and NH 4) involving JT ions of Cu 2+ and Mn 3+ , respectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A 2 CuCl 4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Journal of Alloys and Compounds

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Wide band-gap semiconductors doped with transition-metal ions have attracted a lot of attention i... more Wide band-gap semiconductors doped with transition-metal ions have attracted a lot of attention in the past few years. Here we focus on the spectroscopic properties of Co 2+-doped ZnO in different structural conformations such as single crystal, thin film, nanorods and nanoparticles under different P −T conditions. Optical measurements were obtained by means of Raman and time-resolved spectroscopy using high-pressure techniques. Our main goal is to investigate the pressure-induced Wurtzite-to-Rock-Salt phase transition and how the structural conformation affects the Raman spectra as well as the absorption and emission spectra associated with Co 2+-doped ZnO. The effects of quantum confinement (dimensionality) are also investigated through the distinct spectral features observed in the samples as SC, TF, NW and NP helping us to clarify the still-unassigned absorption and emission spectra in terms of electron-phonon couplings and exchange interactions.

RSC Adv., 2014

The temperature-dependent green luminescence of Y3Ga5O12 nano-garnets doped with different concen... more The temperature-dependent green luminescence of Y3Ga5O12 nano-garnets doped with different concentrations of Er3+ ions has been measured from 300 to 850 K and, in more detail, in the biological range from 292 to 335 K.

Solid State Communications, 1993

The optical properties of [(CH3)4N12MBr4 (M = Cd and Mn) crystals are investigated. Both crystals... more The optical properties of [(CH3)4N12MBr4 (M = Cd and Mn) crystals are investigated. Both crystals are positive biaxial with the principal axes of the optic indicatrix n,,np and n, 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,/cl phase transition temperature is also analyzed.

Journal of Physics: Condensed Matter, 1995

The charge-transfer electronic structure of CuBr42- in (N(CH3)4)2CdBr4 crystals is investigated t... more 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 D2d symmetry of the CuBr42- complex. Some bands are split in the low-temperature spectra by the spin-orbit 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, CuBr42- experiences reorientational motions upon varying the temperature which are correlated with the temperature dependence of the monoclinic beta parameter below the Pmcn to P21c/ phase transition temperature Tcl=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 Tc2=20 K with a thermal hysteresis Delta T=10 K. This new phase transition, which had not previously been detected in the ((CH3)4N)2MBr4 (M=Zn, Mn, Co or Cd) series, would correspond to the monoclinic P21c/ to orthorhombic P212121 transition, confirming the predictions of the universal p-T phase diagrams of the title compounds.

Journal of Alloys and Compounds

Journal of Physics: Conference Series, 2020

The effects of pressure in electronic and vibrational properties of the double perovskite CaCu3Ti... more 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 I m 3 ¯ 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 I m 3 ¯ 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 highligh...

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Cancers, 2021

Head and Neck Cancer (HNC) is the seventh most common cancer worldwide with a 5-year survival fro... more 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 bi...

Journal of Physics: Condensed Matter, 2004

This work investigates the magnetic structure of Rb 2 CuCl 4 as a function of pressure and temper... more This work investigates the magnetic structure of Rb 2 CuCl 4 as a function of pressure and temperature using neutron diffraction. As in most A 2 CuCl 4 layered perovskites, there is a 2D ferromagnetic order within the layers. This behaviour is due to the Jahn-Teller (JT) antiferrodistortive structure of the CuCl 6 units. Rb 2 CuCl 4 undergoes a 3D magnetic transition at T N = 16 K, which mainly depends on the weak antiferromagnetic interlayer interaction. The pressure slightly increases T N , as ∂ T N /∂ P = 0.13 K kbar −1. This behaviour is interpreted in terms of pressure-induced tilts and reduction of interlayer distance, both effects increasing the antiferromagnetic exchange coupling between layers. The results are compared with previous magnetic studies under chemical and hydrostatic pressure along layered perovskites series of [C n H 2n+1 NH 3 ] 2 CuCl 4 (n = 1-3) and BMnF 4 (B = Li, Na, K, Rb, Tl, Cs and NH 4) involving JT ions of Cu 2+ and Mn 3+ , respectively. We show that the ratio of the interlayer to intralayer coupling, and thus the nature of the magnetic order, can be tuned by chemical or hydrostatic pressure along the A 2 CuCl 4 series. The present findings stress the relevance of octahedral tilts on the magnetic behaviour of layered perovskites.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.