Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics

Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044

Spectroscopies et modélisation de verres de silice dopés d'ions de terre rare - influence du co-dopage

This study concerns the role of a co-doping agent on the environment of the rare earth ions in silica glass and its consequences on the spectroscopy of the luminescent element. Two different co-doping agents were studied: aluminium and hafnium ions. The samples of doped and co-doped glasses were obtained by sol-gel process and were studied by different experimental methods: luminescence spectroscopy, FLN spectroscopy, Raman spectroscopy, and EXAFS spectroscopy. In parallel some numerical simulations using molecular dynamics technique were carried out to detail various hypothetical environments. This work highlighted modifications in the rare earth environment by the incorporation of a co-doping agent in a material. These modifications were interpreted as: an increase in the number of non-bridging oxygen improving the rare earth ions solubility in glasses; an increase in the distance between oxygen and the rare-earth ions and a modification of the first neighbours covalence inducing an increase of the crystal field undergone by the luminescent ion; and a reduction of the phonon energy which has for consequence a decrease of luminescence quenching. Molecular dynamics simulations have not revealed a dispersing effect of aluminium on the rare earth clustering. On the other hand, the effect could be clearly observed on the numerical simulations of hafnium-containing glass.Cette étude porte sur le rôle d'un co-dopage sur l'environnement des ions de terre rare dans un verre de silice et ses conséquences sur la spectroscopie de l'élément luminescent. Deux codopages différents ont été étudiés : un co-dopage par des ions aluminium et un par des ions hafnium. Les échantillons de verre dopé et co-dopé ont été obtenus par procédé sol-gel et étudiés par différentes méthodes d'investigations expérimentales : spectroscopie de luminescence, spectroscopie FLN, spectroscopie Raman, spectroscopie EXAFS. En parallèle des observations expérimentales, des simulations numériques par dynamique moléculaire ont été réalisées pour détailler différents environnements hypothétiques. Ce travail a mis en évidence des modifications dans l'environnement proche de la terre rare par l'incorporation de co-dopant dans le matériau qui ont été interprétées comme : une augmentation du nombre d'oxygène non-pontant améliorant la solubilité des ions de terre rare dans le verre ; une augmentation de la distance et une modification de la covalence des premiers voisins par rapport à la terre rare induisant une augmentation du champ cristallin subi par l'ion luminescent et une diminution de l'énergie de phonon réduisant les transferts d'énergie. Les simulations par dynamique moléculaire n'ont pas révélé un effet dispersant de l'aluminium sur les agrégats d'ions de terre rare. Par contre l'effet a pu être clairement observé sur les simulations numériques de verre contenant de l'hafnium

Spectroscopies et modélisation de verres de silice dopés d'ions de terre rare (influence du co-dopage)

Cette étude porte sur le rôle d'un co-dopage sur l'environnement des ions de terre rare dans un verre de silice et ses conséquences sur la spectroscopie de l'élément luminescent. Deux codopages différents ont été étudiés : un co-dopage par des ions aluminium et un par des ions hafnium. Les échantillons de verre dopé et co-dopé ont été obtenus par procédé sol-gel et étudiés par différentes méthodes d'investigations expérimentales : spectroscopie de luminescence, spectroscopie FLN, spectroscopie Raman, spectroscopie EXAFS. En parallèle des observations expérimentales, des simulations numériques par dynamique moléculaire ont été réalisées pour détailler différents environnements hypothétiques. Ce travail a mis en évidence des modifications dans l'environnement proche de la terre rare par l'incorporation de co-dopant dans le matériau qui ont été interprétées comme : une augmentation du nombre d'oxygène non-pontant améliorant la solubilité des ions de terre rare dans le verre ; une augmentation de la distance et une modification de la covalence des premiers voisins par rapport à la terre rare induisant une augmentation du champ cristallin subi par l'ion luminescent et une diminution de l'énergie de phonon réduisant les transferts d'énergie. Les simulations par dynamique moléculaire n'ont pas révélé un effet dispersant de l'aluminium sur les agrégats d'ions de terre rare. Par contre l'effet a pu être clairement observé sur les simulations numériques de verre contenant de l'hafnium.This study concerns the role of a co-doping agent on the environment of the rare earth ions in silica glass and its consequences on the spectroscopy of the luminescent element. Two different co-doping agents were studied: aluminium and hafnium ions. The samples of doped and co-doped glasses were obtained by sol-gel process and were studied by different experimental methods: luminescence spectroscopy, FLN spectroscopy, Raman spectroscopy, and EXAFS spectroscopy. In parallel some numerical simulations using molecular dynamics technique were carried out to detail various hypothetical environments. This work highlighted modifications in the rare earth environment by the incorporation of a co-doping agent in a material. These modifications were interpreted as: an increase in the number of non-bridging oxygen improving the rare earth ions solubility in glasses; an increase in the distance between oxygen and the rare-earth ions and a modification of the first neighbours covalence inducing an increase of the crystal field undergone by the luminescent ion; and a reduction of the phonon energy which has for consequence a decrease of luminescence quenching. Molecular dynamics simulations have not revealed a dispersing effect of aluminium on the rare earth clustering. On the other hand, the effect could be clearly observed on the numerical simulations of hafnium-containing glass.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Large Ti-doped sapphire bulk crystal for high power laser applications

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Thermally driven dual-frequency Q-switching of Nd:YGd2Sc2Al2GaO12 ceramic laser

International audienceMulti-wavelength operation of Q-switched Nd-doped YGd2Sc2Al2GaO12 garnet ceramic lasers has been investigated. Dual-wavelength emission around ~1.06 µm has been demonstrated both in the actively and passively Q-switched configurations. The ratio of output energy between the two laser wavelengths was driven by the temperature elevation caused by pumping. Passively Q-switched operation yields dual-frequency emission of two unsynchronized laser pulses carried by distinct transverse modes whereas active Q-switched configuration offers the possibility of synchronizing emission at the two wavelength

Interface effect on titanium distribution during Ti-doped sapphire crystals grown by the Kyropoulos method

International audienceLarge ingot Ti-doped sapphire crystals were successfully grown by Kyropoulos method. Optical characterization of 10 cm diameter crystals shows non-uniform radial distribution of titanium. The measurements of Ti3+ ion distribution in several slices cut perpendicular to the growth direction show that the concentration is higher at the periphery of the crystal as compared to the central part of the ingot. Numerical modeling is applied to investigate heat transfer, melt convection and species transport during the Kyropoulos growth process. The transient simulation shows an unsteady convection generated by the strong interaction between the flow and the thermal field. The distribution of Ti in the melt is nearly uniform due to the intense convective mixing. The radial distribution of titanium depends mainly on the shape of the crystal-melt interface. The measured U-shaped concentration profile is explained by accounting the conical shape of the interface. High curvatures of the growth interface observed in experiments are explained by the increased thermal conductivity of the sapphire crystal, which is participating to the radiative heat transfer. The interface curvature depends on the absorption coefficient, which is higher for Ti-doped sapphire crystals than for undoped crystals. Therefore, the initial Ti concentration in the melt should be decreased in order to reduce the absorption coefficient and the interface curvature. The comparison of numerically computed titanium distribution in the crystals to experimental measurements shows a good agreement. (C) 2017 Elsevier B.V. All rights reserved

Laser Properties of the Nd:YGd2 Sc2 Al2Ga O12 Garnet Ceramic

CW lasing at 1058.6 and 1061.3 nm was demonstrated with 45% slope efficiency from the Nd:YGd2Sc2Al2GaO12 ceramic. From passive Q-switching, 2 ns pulses with 6.2 μJ energy are obtained at 7.3 kHz repetition rate

Bubbles defects distribution in sapphire bulk crystals grown by Czochralski technique

International audienceSapphire crystals exhibit microscopic defects known as “micro-bubbles or micro-voids”. We have studied micro-bubbles distribution, and their sizes in sapphire crystals grown by Czochralski technique. They are not uniform, depend on the pulling rate and their presence strongly affect the optical properties such as transmission and wavefront quality. The results provide important information about micro-bubbles distribution and the possibilities to minimize their propagation during the growth procedure of sapphire single crystal using Czochralski technique

Titanium distribution in Ti-sapphire single crystals grown by Czochralski and Verneuil technique

International audienceThe distributions of Ti3+ and Ti4+ ions were evaluated by photoluminescence measurement in the wafers cut from different positions of the ingots grown by Czochralski and Verneuil techniques. Particular radial distributions of Ti4+ as function of the position in the ingot were observed in the crystals grown by Verneuil technique different than the crystals grown by Czochralski method