U. Guez-mendoza | EUENSC - Universidad de La Laguna (Tenerife, España) (original) (raw)
Papers by U. Guez-mendoza
Journal of Applied Physics, 2001
Optical properties of Eu3+ ions in oxyfluoride glass ceramics and in the precursor glasses (30 Si... more Optical properties of Eu3+ ions in oxyfluoride glass ceramics and in the precursor glasses (30 SiO2, 15 Al2O3, 29 CdF2, 22 PbF2, 1.5 YF3, and 2.5 EuF3, in mol %) have been analyzed and compared. The Eu3+ ions in the glass ceramics are incorporated into a crystalline environment with higher symmetry and lower energy coupled phonons. Emission measurements indicate that
Journal of Applied Physics, 2003
Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with two differen... more Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with two different concentrations, 0.1 and 1 mol %, have been analyzed and compared with previous results for higher concentrated samples, 2.5 mol %. The Eu3+ ions in the 0.1 mol % doped glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonon
Journal of Applied Physics, 2004
A study of optical properties of Nd3+ doped oxyfluoride glasses and glass ceramics prepared by th... more A study of optical properties of Nd3+ doped oxyfluoride glasses and glass ceramics prepared by three different methods has been carried out. These methods start from NdF3, Nd2O3, or a Nd3+ ion solution as doping agent. The alternative preparation method based on a preliminary dissolution of the Nd3+ ions is proposed in order to avoid nonhomogeneous dopant distribution and spontaneous
Room temperature intense green upconversion emission under excitation at 749 nm in a fluoroindate... more Room temperature intense green upconversion emission under excitation at 749 nm in a fluoroindate glass doped with 2.5 mol% of Ho3+ has been observed. Analysis of spectral measurements suggest a photon avalanche mechanism with emissions from the 5S2 and 5F4 levels of Ho3+ ions.
Journal of Applied Spectroscopy, 1995
Journal of Applied Spectroscopy, 1995
19th Congress of the International Commission for Optics: Optics for the Quality of Life, 2003
Radiation Effects and Defects in Solids, 2003
Optical properties of Eu 3þ ions in oxyfluoride glasses and glass ceramics doped with low concent... more Optical properties of Eu 3þ ions in oxyfluoride glasses and glass ceramics doped with low concentration (0.1 mol%) have been analysed and compared with previous results for high concentrated samples (2.5 mol%). The Eu 3þ ions in the low dopant concentration glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonons energy than in the precursor glasses. Fluorescence line narrowing measurements indicate the presence of two main fluoride site distributions for the Eu 3þ ions in these low concentrated glass ceramics.
Optical Materials, 2012
ABSTRACT
Optical Materials, 2005
Blue, green and red emissions have been generated at room temperature by upconversion processes u... more Blue, green and red emissions have been generated at room temperature by upconversion processes under infrared laser excitation at 750 and 840 nm in fluorozirconate glasses doped with Ho 3+ ions. The intense green emission, associated to the 5 S 2 , 5 F 4 ! 5 I 8 transitions, has been carefully analysed in order to elucidate the mechanisms involved in the energy conversion process. The temporal dynamics of the emission intensities, the extremely weak ground state absorptions, the strong excited state absorptions and the different cross-relaxation processes indicate that two different photon avalanche mechanisms are responsible of the 750 and 840 nm laser-induced upconversion processes in the Ho 3+-doped fluorozirconate glass.
Journal of Physics: Condensed Matter, 2013
We describe the results of x-ray absorption experiments carried out to deduce structural and chem... more We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu 3+ doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-L III edges. The Eu environment in the glass samples is observed to be similar to that of EuF 3. Complementary x-ray diffraction experiments show that thermal annealing creates β-PbF 2 type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-L III edge shows that after the thermal treatment most lead atoms form a PbO amorphous phase and that only 10% of the lead atoms remain available to form β-PbF 2 type nanocrystals. Both x-ray diffraction and absorption point to a high Eu content in the nanocrystals. Our study suggests new approaches to the oxyfluoride glass-ceramic synthesis in order to further improve their properties.
Journal of Nanoscience and Nanotechnology, 2012
ABSTRACT Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a c... more ABSTRACT Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a citrate sol-gel technique. The structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The materials are found to exist in single phase of cubic garnet structure with an average particle size of around 45 nm. The Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnet powders give rise to an intense green and weak red emission of Ho3+ ions under 457.5 nm direct excitation. Moreover, when the Yb3+ ions are excited at 950 nm a very bright green luminescence of the Ho3+ ions is observed by the naked eyes even for such low laser power as 10 mW and the intensity of the red emission have been increased compared to that found under direct excitation of the Ho3+ ions. The power dependency and dynamics of the infrared-to-visible upconverted luminescence confirm the existence of different two-photon energy transfer processes. All these results have been compared with those obtained for other garnets doped with similar lanthanide ions which suggest that the Lu3Ga5O12 nano-garnets are potential materials for light emitting devices.
Journal of Luminescence, 2011
The optical properties of Er 3 + ions in a novel glass based on TeO 2-PbF 2-AlF 3 oxyfluoride tel... more The optical properties of Er 3 + ions in a novel glass based on TeO 2-PbF 2-AlF 3 oxyfluoride tellurites have been investigated using steady-state and time-resolved spectroscopies as a function of the rare-earth doping concentration. Basic optical characterizations have been performed measuring and calculating the absorption and emission spectra and the cross-sections, the Judd-Ofelt intensity parameters, the radiative probabilities and the fluorescence decays and lifetimes. Special attention has been devoted to the broad 4 I 13/2-4 I 15/2 emission transition at around 1.53 mm since, with a wide broadening of around 70 nm and a relative long lifetime of around 3 ms compared to others glass hosts, it shows potential applications in the design of erbium-doped fiber amplifiers. The absorption, the stimulated emission and the gain cross-sections of this transition have been obtained and compared with that obtained in different hosts. Finally, infrared-to-visible upconversion processes exciting at around 800 nm have been analyzed and different mechanisms involved in the energy conversion have been proposed.
Journal of Luminescence, 1994
Photon avalanche up-conversion emission at 550 nm with a steep threshold has been observed in Er-... more Photon avalanche up-conversion emission at 550 nm with a steep threshold has been observed in Er-doped ZBLAN glass. This is, to the best of our knowledge, the first time that this effect was found for Er 3+ ion, in a glass, and at room temperature. The excitation wavelength is ...
![Research paper thumbnail of Ultraviolet and visible upconversion luminescence in Nd[sup 3+]-doped oxyfluoride glasses and glass ceramics obtained by different preparation methods](https://attachments.academia-assets.com/69922243/thumbnails/1.jpg)
](Journal of Applied Physics, 2006
Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and c... more Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and compared in Nd 3+-doped oxyfluoride glasses and glass ceramics prepared by different methods. The mechanisms involved in such processes have been analyzed. A spectroscopy study comparing absorption and upconversion excitation spectra has been carried out in order to discern in each case the mechanism involved in the origin of the upconversion emissions, i.e., two-or three-photon involved excited state absorption or energy transfer processes. The shape of the absorption and emission spectra and the relative upconversion efficiencies have been compared and explained taking into account the final distribution of the luminescent ions in the glassy and nanocrystalline phases.
![Research paper thumbnail of Spectral investigations on Dy[sup 3+]-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics](https://attachments.academia-assets.com/69922250/thumbnails/1.jpg)
](Journal of Applied Physics, 2009
Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and... more Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the 4 F 9/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy 3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 m, useful for optical amplification in fiber amplifiers.
High Pressure Research, 2002
Amorphization is observed from the 5 D 0 ! 7 F 0,1,2 emission spectra of the Eu 3þ ions in EuZrF ... more Amorphization is observed from the 5 D 0 ! 7 F 0,1,2 emission spectra of the Eu 3þ ions in EuZrF 7 polycrystal measured at different pressures at room temperature. The crystalline phase progressively transforms to amorphous when the pressure is increased over 2 GPa. Compression of the EuZrF 7 crystalline phase results in an increase in the number of non-equivalent environments of the Eu 3þ ions with different crystal-field strengths. Simultaneously, an apparent loss of the long-range order, being typical for amorphous materials like glasses, can be observed, yielding similar emission spectra for the Eu 3þ ions as in the case of the fluorozirconate glasses. In these materials the local structure of the Eu 3þ ions is at least as low as the C S symmetry of the EuZrF 7 phase and their coordination number does not differ significantly from the eight-fold coordinated Eu 3þ ions found in the crystalline phase. Amorphization is retained after pressure release.
High Pressure Research, 2006
Optical properties of the SrWO 4 matrix doped with different Eu 3+ concentrations (10%, 13% and 2... more Optical properties of the SrWO 4 matrix doped with different Eu 3+ concentrations (10%, 13% and 20%) have been studied. At ambient pressure, the temporal evolution of the emissions from the 5 D 1 level has been analyzed in the different doped crystals in order to discuss the energy transfer processes between the Eu 3+ ions. This study lets conclude that the Eu 3+ ions are randomly distributed in the matrix. Moreover, the 5 D 0 → 7 F 1,2 emissions have been measured increasing the pressure up to 15 GPa in order to analyze the changes in the Eu 3+ local structure. The results confirm the existence of a structural phase transition around 8.5 GPa.
Journal of Applied Physics, 2006
The doping distribution of Tm3+ ions in a transparent oxyfluoride glass ceramic has been investig... more The doping distribution of Tm3+ ions in a transparent oxyfluoride glass ceramic has been investigated. Optical absorption, luminescence, and excitation measurements have been performed in order to determine the environment in which Tm3+ ions and the infrared emissions they give rise to are located. An interesting result has been found: the main contribution to the 1465 nm emission (S band)
Journal of Applied Physics, 2001
Optical properties of Eu3+ ions in oxyfluoride glass ceramics and in the precursor glasses (30 Si... more Optical properties of Eu3+ ions in oxyfluoride glass ceramics and in the precursor glasses (30 SiO2, 15 Al2O3, 29 CdF2, 22 PbF2, 1.5 YF3, and 2.5 EuF3, in mol %) have been analyzed and compared. The Eu3+ ions in the glass ceramics are incorporated into a crystalline environment with higher symmetry and lower energy coupled phonons. Emission measurements indicate that
Journal of Applied Physics, 2003
Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with two differen... more Optical properties of Eu3+ ions in oxyfluoride glasses and glass ceramics doped with two different concentrations, 0.1 and 1 mol %, have been analyzed and compared with previous results for higher concentrated samples, 2.5 mol %. The Eu3+ ions in the 0.1 mol % doped glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonon
Journal of Applied Physics, 2004
A study of optical properties of Nd3+ doped oxyfluoride glasses and glass ceramics prepared by th... more A study of optical properties of Nd3+ doped oxyfluoride glasses and glass ceramics prepared by three different methods has been carried out. These methods start from NdF3, Nd2O3, or a Nd3+ ion solution as doping agent. The alternative preparation method based on a preliminary dissolution of the Nd3+ ions is proposed in order to avoid nonhomogeneous dopant distribution and spontaneous
Room temperature intense green upconversion emission under excitation at 749 nm in a fluoroindate... more Room temperature intense green upconversion emission under excitation at 749 nm in a fluoroindate glass doped with 2.5 mol% of Ho3+ has been observed. Analysis of spectral measurements suggest a photon avalanche mechanism with emissions from the 5S2 and 5F4 levels of Ho3+ ions.
Journal of Applied Spectroscopy, 1995
Journal of Applied Spectroscopy, 1995
19th Congress of the International Commission for Optics: Optics for the Quality of Life, 2003
Radiation Effects and Defects in Solids, 2003
Optical properties of Eu 3þ ions in oxyfluoride glasses and glass ceramics doped with low concent... more Optical properties of Eu 3þ ions in oxyfluoride glasses and glass ceramics doped with low concentration (0.1 mol%) have been analysed and compared with previous results for high concentrated samples (2.5 mol%). The Eu 3þ ions in the low dopant concentration glass ceramics are diluted into like crystalline environments with higher symmetry and lower coupled phonons energy than in the precursor glasses. Fluorescence line narrowing measurements indicate the presence of two main fluoride site distributions for the Eu 3þ ions in these low concentrated glass ceramics.
Optical Materials, 2012
ABSTRACT
Optical Materials, 2005
Blue, green and red emissions have been generated at room temperature by upconversion processes u... more Blue, green and red emissions have been generated at room temperature by upconversion processes under infrared laser excitation at 750 and 840 nm in fluorozirconate glasses doped with Ho 3+ ions. The intense green emission, associated to the 5 S 2 , 5 F 4 ! 5 I 8 transitions, has been carefully analysed in order to elucidate the mechanisms involved in the energy conversion process. The temporal dynamics of the emission intensities, the extremely weak ground state absorptions, the strong excited state absorptions and the different cross-relaxation processes indicate that two different photon avalanche mechanisms are responsible of the 750 and 840 nm laser-induced upconversion processes in the Ho 3+-doped fluorozirconate glass.
Journal of Physics: Condensed Matter, 2013
We describe the results of x-ray absorption experiments carried out to deduce structural and chem... more We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu 3+ doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-L III edges. The Eu environment in the glass samples is observed to be similar to that of EuF 3. Complementary x-ray diffraction experiments show that thermal annealing creates β-PbF 2 type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-L III edge shows that after the thermal treatment most lead atoms form a PbO amorphous phase and that only 10% of the lead atoms remain available to form β-PbF 2 type nanocrystals. Both x-ray diffraction and absorption point to a high Eu content in the nanocrystals. Our study suggests new approaches to the oxyfluoride glass-ceramic synthesis in order to further improve their properties.
Journal of Nanoscience and Nanotechnology, 2012
ABSTRACT Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a c... more ABSTRACT Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a citrate sol-gel technique. The structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The materials are found to exist in single phase of cubic garnet structure with an average particle size of around 45 nm. The Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnet powders give rise to an intense green and weak red emission of Ho3+ ions under 457.5 nm direct excitation. Moreover, when the Yb3+ ions are excited at 950 nm a very bright green luminescence of the Ho3+ ions is observed by the naked eyes even for such low laser power as 10 mW and the intensity of the red emission have been increased compared to that found under direct excitation of the Ho3+ ions. The power dependency and dynamics of the infrared-to-visible upconverted luminescence confirm the existence of different two-photon energy transfer processes. All these results have been compared with those obtained for other garnets doped with similar lanthanide ions which suggest that the Lu3Ga5O12 nano-garnets are potential materials for light emitting devices.
Journal of Luminescence, 2011
The optical properties of Er 3 + ions in a novel glass based on TeO 2-PbF 2-AlF 3 oxyfluoride tel... more The optical properties of Er 3 + ions in a novel glass based on TeO 2-PbF 2-AlF 3 oxyfluoride tellurites have been investigated using steady-state and time-resolved spectroscopies as a function of the rare-earth doping concentration. Basic optical characterizations have been performed measuring and calculating the absorption and emission spectra and the cross-sections, the Judd-Ofelt intensity parameters, the radiative probabilities and the fluorescence decays and lifetimes. Special attention has been devoted to the broad 4 I 13/2-4 I 15/2 emission transition at around 1.53 mm since, with a wide broadening of around 70 nm and a relative long lifetime of around 3 ms compared to others glass hosts, it shows potential applications in the design of erbium-doped fiber amplifiers. The absorption, the stimulated emission and the gain cross-sections of this transition have been obtained and compared with that obtained in different hosts. Finally, infrared-to-visible upconversion processes exciting at around 800 nm have been analyzed and different mechanisms involved in the energy conversion have been proposed.
Journal of Luminescence, 1994
Photon avalanche up-conversion emission at 550 nm with a steep threshold has been observed in Er-... more Photon avalanche up-conversion emission at 550 nm with a steep threshold has been observed in Er-doped ZBLAN glass. This is, to the best of our knowledge, the first time that this effect was found for Er 3+ ion, in a glass, and at room temperature. The excitation wavelength is ...
Journal of Applied Physics, 2006
Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and c... more Ultraviolet and visible upconversion emissions under infrared excitation have been obtained and compared in Nd 3+-doped oxyfluoride glasses and glass ceramics prepared by different methods. The mechanisms involved in such processes have been analyzed. A spectroscopy study comparing absorption and upconversion excitation spectra has been carried out in order to discern in each case the mechanism involved in the origin of the upconversion emissions, i.e., two-or three-photon involved excited state absorption or energy transfer processes. The shape of the absorption and emission spectra and the relative upconversion efficiencies have been compared and explained taking into account the final distribution of the luminescent ions in the glassy and nanocrystalline phases.
Journal of Applied Physics, 2009
Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and... more Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the 4 F 9/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy 3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 m, useful for optical amplification in fiber amplifiers.
High Pressure Research, 2002
Amorphization is observed from the 5 D 0 ! 7 F 0,1,2 emission spectra of the Eu 3þ ions in EuZrF ... more Amorphization is observed from the 5 D 0 ! 7 F 0,1,2 emission spectra of the Eu 3þ ions in EuZrF 7 polycrystal measured at different pressures at room temperature. The crystalline phase progressively transforms to amorphous when the pressure is increased over 2 GPa. Compression of the EuZrF 7 crystalline phase results in an increase in the number of non-equivalent environments of the Eu 3þ ions with different crystal-field strengths. Simultaneously, an apparent loss of the long-range order, being typical for amorphous materials like glasses, can be observed, yielding similar emission spectra for the Eu 3þ ions as in the case of the fluorozirconate glasses. In these materials the local structure of the Eu 3þ ions is at least as low as the C S symmetry of the EuZrF 7 phase and their coordination number does not differ significantly from the eight-fold coordinated Eu 3þ ions found in the crystalline phase. Amorphization is retained after pressure release.
High Pressure Research, 2006
Optical properties of the SrWO 4 matrix doped with different Eu 3+ concentrations (10%, 13% and 2... more Optical properties of the SrWO 4 matrix doped with different Eu 3+ concentrations (10%, 13% and 20%) have been studied. At ambient pressure, the temporal evolution of the emissions from the 5 D 1 level has been analyzed in the different doped crystals in order to discuss the energy transfer processes between the Eu 3+ ions. This study lets conclude that the Eu 3+ ions are randomly distributed in the matrix. Moreover, the 5 D 0 → 7 F 1,2 emissions have been measured increasing the pressure up to 15 GPa in order to analyze the changes in the Eu 3+ local structure. The results confirm the existence of a structural phase transition around 8.5 GPa.
Journal of Applied Physics, 2006
The doping distribution of Tm3+ ions in a transparent oxyfluoride glass ceramic has been investig... more The doping distribution of Tm3+ ions in a transparent oxyfluoride glass ceramic has been investigated. Optical absorption, luminescence, and excitation measurements have been performed in order to determine the environment in which Tm3+ ions and the infrared emissions they give rise to are located. An interesting result has been found: the main contribution to the 1465 nm emission (S band)