Embora cristais boratos dopados com ions de terras raras sejam amplamente investigados, vidros boratos desses sistemas vêm sendo pouco estudados. O cristal NdAl3(BO3)4(NAB) cujas propriedades laser e de geração de segundo harmônico (GSH) são conhecidas e continuamente relatadas na literatura, vem sendo recentemente considerado como um forte candidato para dispositivo \"microchip laser\". Alem disso, cristais dopados com íons de neodímio têm demonstrado ser excelentes para o bombeio com laseres de diodo, devido ao intenso pico de absorção próximo a 800 nm. Entretanto, existe na literatura um número muito limitado de estudos relatando as propriedades de vidros do sistema Nd2O3-Al2-O3-B2O3. Partindo dessa premissa, o objetivo principal deste trabalho foi obter vidros neste sistema, para elevadas concentrações de Nd2O3 (5-20 mol%), por meio das técnicas de fusão/moldagem convencional e fusão a laser. Dentre os materiais preparados foram obtidos três vidros transparentes, um material com separação de fases e, onde ocorreu cristalização. Os vidros obtidos, NAB136, NAB152560 e NAB226 foram caracterizados através das técnicas de análise térmica diferencial (ATD), difratometria de raios X (DRX), absorção óptica (AO) e ICP-OES (análise de composição). De acordo como os resultados de ATD, os vidros não apresentaram uma variação significativa na temperatura de transição vítrea (Tg) com o aumento da concentração de Nd2O3. O vidro NAB136, obtido com composição próxima a do cristal NdAl3(BO3)4(NAB), foi submetido a um tratamento térmico de cristalização a uma temperatura de 820°C por 2 horas. Os resultados de DRY indicaram a presença das fases cristalinas majoritárias Al4B2O9 e NAB. Medidas de absorção Óptica (AO) dos vidros no intervalo espectral de 300-1000 nm indicaram intensa absorção nos comprimentos de onda 500 nm e 800 nm. As análises de ICP-OES indicaram alta pureza dos vidros e composições próximas das composições nominais / Although borate crystals doped with rare earth ions have already been extensively investigated, borate glasses of these systems were not widely studied. The NdAl3(BO3)4(NAB) crystal, which laser and second harmonic generation (SGH) properties are well know and continuously mentioned in literature, has been recently considered as a strong candidate for microchip laser devices. Moreover, neodymium doped crystals are known for their excellent performance when pumped with diode lasers due to its intense absorption peak near to 800 nm. However, a limited number of papers have been published referring to the properties of glasses in the system Nd2O3-Al2-O3-B2O3. Based on this premise, the main purpose of this work was to prepare glasses in this system for Nd2O3 elevate concentrations (5-20 mol%) by the conventional melting/molding and laser heated methods. Among the prepared materials it was obtained three clear glasses, a material with phase separation and another one, which has crystallized. The obtained glasses, NAB136, NAB152560 and NAB226, where characterized by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical absorption (OA) and ICP-OES (compositional analysis). According to the DTA results, the glasses have not presenteá a rneaningfut change in the glass transition temperature (Tg) with the increase of Nd2O3 content. The NAB136 glass, with the closest composition to the crystal NdAl3(BO3)4(NAB), was submitted to a crystallization thermal treatment at 820°C for 2 hours. XRD results showed the existence of the main crystalline phases and NAB. Optical absorption (OA) measurements of the glasses in the spectral range 300-1000 nm indicated intense absorpâion in the 500 nm and 800 nm wavelengths. ICP-OES analysis showed that the glasses posses high purity stoichiometry, close to the nominal ones

Embora cristais boratos dopados com ions de terras raras sejam amplamente investigados, vidros boratos desses sistemas vêm sendo pouco estudados. O cristal NdAl3(BO3)4(NAB) cujas propriedades laser e de geração de segundo harmônico (GSH) são conhecidas e continuamente relatadas na literatura, vem sendo recentemente considerado como um forte candidato para dispositivo \"microchip laser\". Alem disso, cristais dopados com íons de neodímio têm demonstrado ser excelentes para o bombeio com laseres de diodo, devido ao intenso pico de absorção próximo a 800 nm. Entretanto, existe na literatura um número muito limitado de estudos relatando as propriedades de vidros do sistema Nd2O3-Al2-O3-B2O3. Partindo dessa premissa, o objetivo principal deste trabalho foi obter vidros neste sistema, para elevadas concentrações de Nd2O3 (5-20 mol%), por meio das técnicas de fusão/moldagem convencional e fusão a laser. Dentre os materiais preparados foram obtidos três vidros transparentes, um material com separação de fases e, onde ocorreu cristalização. Os vidros obtidos, NAB136, NAB152560 e NAB226 foram caracterizados através das técnicas de análise térmica diferencial (ATD), difratometria de raios X (DRX), absorção óptica (AO) e ICP-OES (análise de composição). De acordo como os resultados de ATD, os vidros não apresentaram uma variação significativa na temperatura de transição vítrea (Tg) com o aumento da concentração de Nd2O3. O vidro NAB136, obtido com composição próxima a do cristal NdAl3(BO3)4(NAB), foi submetido a um tratamento térmico de cristalização a uma temperatura de 820°C por 2 horas. Os resultados de DRY indicaram a presença das fases cristalinas majoritárias Al4B2O9 e NAB. Medidas de absorção Óptica (AO) dos vidros no intervalo espectral de 300-1000 nm indicaram intensa absorção nos comprimentos de onda 500 nm e 800 nm. As análises de ICP-OES indicaram alta pureza dos vidros e composições próximas das composições nominais / Although borate crystals doped with rare earth ions have already been extensively investigated, borate glasses of these systems were not widely studied. The NdAl3(BO3)4(NAB) crystal, which laser and second harmonic generation (SGH) properties are well know and continuously mentioned in literature, has been recently considered as a strong candidate for microchip laser devices. Moreover, neodymium doped crystals are known for their excellent performance when pumped with diode lasers due to its intense absorption peak near to 800 nm. However, a limited number of papers have been published referring to the properties of glasses in the system Nd2O3-Al2-O3-B2O3. Based on this premise, the main purpose of this work was to prepare glasses in this system for Nd2O3 elevate concentrations (5-20 mol%) by the conventional melting/molding and laser heated methods. Among the prepared materials it was obtained three clear glasses, a material with phase separation and another one, which has crystallized. The obtained glasses, NAB136, NAB152560 and NAB226, where characterized by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical absorption (OA) and ICP-OES (compositional analysis). According to the DTA results, the glasses have not presenteá a rneaningfut change in the glass transition temperature (Tg) with the increase of Nd2O3 content. The NAB136 glass, with the closest composition to the crystal NdAl3(BO3)4(NAB), was submitted to a crystallization thermal treatment at 820°C for 2 hours. XRD results showed the existence of the main crystalline phases and NAB. Optical absorption (OA) measurements of the glasses in the spectral range 300-1000 nm indicated intense absorpâion in the 500 nm and 800 nm wavelengths. ICP-OES analysis showed that the glasses posses high purity stoichiometry, close to the nominal ones

L’éclairage par « LEDs blanches » est devenu un enjeu majeur afin d’élaborer des dispositifs à bas coût, produisant une lumière confortable pour l’œil en évitant de forte composante bleue nocive pour la vue et la santé. A l’Institut Néel, nous développons un nouveau type de luminophores à base de poudres d’aluminoborate d’yttrium. Le caractère innovant de ces poudres est de produire une large bande d’émission dans l’ensemble du spectre visible, à partir de défauts structuraux présents dans la matrice amorphe. Ainsi ces luminophores permettraient de générer un éclairage blanc sous l'excitation de LED émettant dans le proche UV (370-390 nm). De plus, ces matériaux n’ont pas de lanthanides, ce qui réduit leur coût.Les luminophores d’aluminoborate d’yttrium ont dans un premier temps été préparés par la méthode des précurseurs polymériques, impliquant plusieurs étapes de recuits sous atmosphères contrôlées à des températures relativement élevées (700-740°C). Le travail de thèse a porté dans un premier temps sur la mise au point de la synthèse par voie sol-gel. Ces travaux ont permis de réduire simultanément les durées du procédé et les températures des traitements thermiques (450-650°C), ainsi que la perte de masse globale par décomposition des fonctions organiques des précurseurs.Par analyses thermiques (ATD, ATG) couplée à la spectrométrie de masse et RMN 13C, nous avons caractérisé la présence de résidus carbonés dans les poudres lorsqu’elles présentent de la luminescence. Néanmoins, une partie de ces résidus carbonés se trouvent sous forme de carbone pyrolytique (carbones aromatiques) qui entrainent une réabsorption partielle de la luminescence émise dans le visible, entrainant ainsi une diminution de l’intensité d’émission. Les caractérisations structurales (DRX, FTIR, RMN) menées sur les poudres ont montré que la première phase cristalline apparaissant pour les deux méthodes de synthèse est une phase d’aluminoborate Al4B2O9. L’étude par Fonction de Distribution de Paires (PDF) montre que la matrice aluminoborate amorphe présente un ordre local proche de la phase Al4B2O9, à savoir une organisation tridimensionnelle cyclique de métaux pontés par des ligands oxo ou hydroxo de 6 à 10 chaînons. D’autre part, sur la base des résultats RMN 13C, l’yttrium semble garder dans sa sphère de coordination des ligands propionates jusqu’à hautes températures. Par ailleurs, la présence d’espèces radicalaires dans les poudres luminescentes a été mise en évidence par résonnance paramagnétique électronique. Un ensemble de mesures à différentes fréquences, en mode continu et pulsé, ont permis d’attribuer ces espèces à des radicaux carbonés. Les études de photoluminescence non-résolues et résolues en temps, couplées à des analyses de thermoluminescence ont mis en évidence la présence de plusieurs espèces luminescentes présentant essentiellement des propriétés de fluorescence (durée de vie de quelques ns) mais aussi une très faible part de phosphorescence (durée de vie de la ms à plusieurs s). Les poudres synthétisées par voie sol-gel présentent un rendement quantique interne d’environ 30 %.Aux vues des différentes analyses, les poudres luminescentes synthétisées par voie sol-gel semblent contenir deux types de résidus carbonés : l’un à l’origine des propriétés de photoluminescence et l’autre défavorable (carbone pyrolytique piégé) car absorbant partiellement l’émission de luminescence. En conclusion, nous proposons un mécanisme de photoluminescence extrinsèque, basé sur des centres carbonés dispersés au sein de la matrice minérale, favorisant majoritairement la fluorescence dans le bleu (bande centrée vers 430 nm) et dans le vert (bande centrée vers 500 nm) mais aussi une faible proportion de phosphorescence émettant dans la même gamme de longueurs d’onde. / White solid state lighting is recognized as a major disruptive technology with an urgent need of low coast prices, associated to good color quality, confortable for eyes, by reducing the bluish harmful contribution of “cold” lighting. At Néel Institute, we develop a new type of phosphors based on yttrium aluminoborate powders. These innovating powders exhibit a large emission band on the whole visible range, arising from structural defects in the amorphous matrix. Thus, with a single phosphor, one can generate warm white lighting through the excitation of LEDs emitting in the near UV (370-390 nm). Moreover, these phosphors don’t possess lanthanides, making them less expensive.The powders synthesized by chimie douce routes, are annealed under controlled atmosphere. The yttrium alominoborate phosphors were first prepared by the polymercic precursor method. This synthesis road involved several steps and relatively high annealing temperatures (700-740°C). This thesis was focused on the sol-gel synthesis method. By this work, the duration process, the annealing temperature (450°C-650°C), and the global mass loss incoming from the organic precursors decomposition were significantly reduced.Thermal analysis (TDA-TG) coupled with mass spectrometry and 13C RNM show residual carbon groups in luminescent powders. Nevertheless, one part of the residual carbons is pyrolytic carbon (aromatic carbon), which leads to partial re-absorption of the visible emitted luminescence, and thus induces a decrease of the emission intensity.The structural characterizations of yttrium aluminoborate powders (XRD, FTIR, NMR) show that Al4B2O9 aluminoborate phase, is the first appearing crystalline phase during the increase of calcination temperature. The Pair Distribution Function (PDF) study demonstrates that amorphous aluminoborate matrix exhibit a short range ordering close to Al4B2O9 phase: a cyclic tridimensional organization of metal bridges by oxo or hydroxo ligands. On the other hand, based on 13C NMR results, yttrium seems to conserve propionate ligands in its coordination sphere until high temperature. Otherwise, the presence of radical species was evidenced in luminescent powders by electronic paramagnetic resonance. A set of measurements performed at different frequencies, in continuous and pulsed modes, allows attributing that species to carbon radicals. The presence of several luminescence species exhibiting essentially fluorescence properties (ns life time) and very weak phosphorescence emission (ms and s lifetime) was shown by the means of photoluminescence studies steady-state and time resolved coupled to thermoluminescence analysis. The powders synthesized by sol-method exhibit a 30 % internal quantum yield.Thanks to the different characterizations, luminescent powders synthesized by the sol-gel route seem to contain two types of residual carbons: one at the origin of the luminescence properties (carbon-related radicals) while the other, pyrolytic carbon, is damaging as it absorbs partially the luminescence emission. To conclude, we suggest an extrinsic mechanism for the photoluminescence, which is based on carbon centers dispersed inside the mineral matrix, favoring mainly fluorescence in blue (430 nm) and green emissions (500 nm) associated with a weak phosphorescence emission in the same emission range.

This work specifies the synthesis and the characterization of amorphous powders belonging to the Y2O3 - Al2O3 - B2O3 system. The main objective of this work was to develop amorphous powders near the YAl3(BO3)4 composition without any rare earth as doping for the development of a new family of phosphors for solid state lighting systems excited by near ultra-violet light. The sol-gel and polymeric precursor methods were applied in order to produce these powders. After these syntheses we optimized several parameters such as thermal treatments: two different routes were tested: direct calcination and pyrolytic decomposition followed by calcination. The temperature, annealing time, heating rate and the effects of impurities on the photoluminescence (PL) were studied. A comparison between these two synthesis methods was done. The powder samples were characterized by thermal analysis technique, X-ray diffraction, photoluminescence and infra-red spectroscopies, transmission and scanning electron microscopy, elemental analysis and electron probe microanalyses, nuclear magnetic resonance, cathodoluminescence, electronic paramagnetic resonance. From the thermal analyzes, it was observed that the powder prepared by polymeric precursor method shows a glass transition temperature (Tg) around 740 °C and crystallization temperatures (Tx) at 815, 850 and 900 °C. Amorphous powder showing high photoluminescence emission (between 400 and 750 nm) and quantum yields higher than 90% at 365 nm excitation, without any phase segregation were obtained when the samples are annealed at temperatures at around Tg, above this temperatures the powder start to crystallize decreasing their PL properties. Other compositions were studied by increasing the relative amounts of Y2O3, Al2O3 and B2O3, by removing the yttrium, addition of SiO2. Finally, the first measurements of color coordinates and the preliminary tests on the thermal and photo stability have been done. / Ce travail de these porte sur la synthèse et la caractérization de poudres amorphes en appartenant système Y2O3 - Al2O3 - B2O3. L'objectif principal du travail a été de préparer des poudres amorphes dont la composition est proche de YAl3(BO3)4 sans terre rare en vue la réalisation de phosphores pour des dispositif d'éclairage solide à base de LED emmetant dans le proche UV. Pour la synthèse des poudres les methodes sol-gel et celles des precurseurs polymériques ont été utilisées. Nous avons ensuite optimizé les paramètres thermiques, en utilisant deux stratégies: la calcination directe et la pyrolyse suivrie d'une seconde étape de calcination. La température, le temps de recuit, vitesse de chauffage et les effect des impurities sur la photoluminescence ont été étudié. Les échantillons en poudre ont été caractérisés par les techniques d'analyse thermiques, diffraction des rayons X, la spectroscopie de photoluminescence et la spectroscopie infra-rouge, microscopies électronique à balayage et en transmission, les méthodes des analyses élémentaire et microsonde électronique, la résonance magnétique nucléaire, cathodoluminescence et le résonance paramagnétique électronique. Par l'analyse thermique, on a observé que la poudre préparée par la méthode de précurseur polymère a une température de transition vitreuse (Tg) autour de 740 ° C et des températures de cristallisation (Tx) à 815, 850 et 900 ° C. Les poudres amorphes presentent de larges bandes d'émission de photoluminescence (entre 400 et 750 nm) avec des rendements quantiques supérieurs à 90% pour une excitation de 365 nm. De plus, les poudres microscopiques obtenu sont chimiquement homogene avec des composition très proche de celle initialmente visée YAl3(BO3)4 lorsque les échantillons sont recuits à des températures voisine du Tg. Au-dessus de cette température, la poudre commence à se cristalliser conduisant à réduction de l'intensité de PL. D'autres compositions ont été étudiées en augmentant la quantité relative de Y2O3, Al2O3 et B2O3, en éliminant complètement l'yttrium, ou en ajutant SiO2. Finalement, les premiers mesures de coordonnées de couleur et les essais préliminaires sur la stabilité thermique et photométrique sont très prometeur. En effet, outres les rendemente specifiques de luminescence très elevés ces luminophores émitent de lumiére très chaudes.