Actuellement, la qualité de l’imagerie provenant de systèmes optiques spatiaux est limitée par la taille de leurs miroirs et la masse des structures supportant le miroir. Le développement de systèmes athermiques légers (un seul matériau) constitue le principal challenge dans l’amélioration de ces systèmes. De matériaux légers, résistants mécaniquement (E/ρ3 > 10, σf > 100 MPa) et stables thermiquement (< 2,0.e-6/K) doivent être développés. Dans ce cadre, notre travail porte sur l’élaboration de composites céramiques associant un matériau à coefficient de dilatation thermique (CTE) positif résistant mécaniquement (alumine ou zircone cériée) et un matériau à CTE très négatif (tungstate de zirconium ou β-eucryptite). L'étude du tungstate de zirconium a révélé plusieurs problèmes de décomposition et de réactions avec certaines matrices oxydes, menant à l’abandon de cet oxyde dans l’élaboration des composites. Dans le cas de la β-eucryptite, un phénomène de vermiculation a été mis en évidence, conduisant à la formation d’une porosité intragranulaire. L’optimisation des paramètres de frittage a permis de limiter cette porosité. L’étude du comportement thermique de la β-eucryptite confirme que son CTE très négatif provient principalement d’un phénomène de fissuration, généré par l’anisotropie de dilatation de sa maille cristalline. Cette fissuration est dépendante de la taille des grains mais également de la taille des agrégats de grains dans le cas des poudres. Ainsi, bien que le CTE intrinsèque de la β-eucryptite soit très faible (-0,4.e-6/K), son CTE extrinsèque peut atteindre des valeurs jusqu'à -10,9.e-6/K selon les conditions d’élaboration. Dans ce travail, deux stratégies d’élaboration de composites sont étudiées. Le premier cas consiste à diminuer le CTE des matrices oxydes à partir d’une poudre de β-eucryptite non microfissurée (-0,4.e-6/K) tandis que le second cas consiste à obtenir des matériaux à CTE très faible à partir d’une poudre de β-eucryptite microfissurée (-3,0.e-6/K). Lors de l’utilisation de la matrice en zircone cériée, le taux de dopage au cérium est optimisé afin de limiter la transformation de phase de la zircone. Cette transformation, induite par les contraintes de tension exercées par la β-eucryptite, affecte la linéarité du comportement thermique du composite. Dans les deux cas d’étude, les composites denses montrent une modification du CTE intrinsèque de la β-eucryptite passant de -0,4.e-6/K à plus de +3,2.e-6/K en raison des contraintes de compression appliquées par la matrice (alumine ou zircone cériée). La relaxation de ces contraintes nécessite une sous-densification des composites. A partir de ces observations, différents composites à CTE très faible sont élaborés. Toutefois, le sous-frittage des composites associé à la microfissuration de la β-eucryptite diminuent fortement les propriétés mécaniques des matériaux ainsi élaborés. / High resolution satellite imagery from space optical systems is mainly limited by the mirror size and the mass of structures supporting the mirror. Nowadays, the development of light athermal systems is the major challenge to improve these optical systems. So, light materials having good mechanical properties (E/ρ3 > 10, σf > 100 MPa) and thermal stability (< 2.0e-6/K) are required. Within this context, our project consists in processing new ceramic composites by combining positive thermal expansion coefficient (TEC) materials having good mechanical properties (alumina or ceria doped zirconia) and negative TEC materials (zirconium tungstate or β-eucryptite) The processing of zirconium tungstate-based materials showed several decomposition and chemical reactions with some oxide matrix leading to its giving up. In the case of β-eucryptite, vermicular phenomenon occurs during sintering leading to the formation of intragranular porosity. Sintering parameters optimization can limit this porosity. The study of the thermal behavior of pure β-eucryptite materials shows that the very negative TEC results from microcracking, generated by the TEC anisotropy of its crystal lattice. This microcracking depends on the grain size and the aggregate size in the case of powder materials. Despite the fact that the TEC of its lattice (called intrinsic TE C equals to -0.4e-6/K) is very low, its bulk (or extrinsic) TEC can reach values until -10.9e-6/K according to the processing conditions. In this work, two strategies for developing composites were studied. The first one consists in decreasing the matrix TEC using an uncracked β-eucryptite powder (-0.4e-6/K) while the second one consists in elaborating near zero TEC materials from a microcracked β-eucryptite powder (-3.0e-6/K). When ceria-doped zirconia is used, ceria content must be adjusted in order to limit zirconia phase transformation. This transformation is driven by tensile stresses induced by the β-eucryptite and modifies the composite thermal behavior linearity. In both studied cases, dense composites show a modification of the β-eucryptite intrinsic TEC from -0.4e-6/K to more than +3.2e-6/K as a consequence of compressive stresses applied by the oxide matrix. An uncompleted densification of composites is required to relax these stresses. Taking into account these observations, several very low TEC composites were elaborated. However, the uncompleted densification of composites and the β-eucryptite microcracking greatly decrease the mechanical properties of these materials.

O emprego de TiO2, na qualidade de semicondutor mais comumente utilizado em fotocatálise heterogênea adquire relevância, devido à sua eficiência na decomposição de poluentes da água, do ar, bactérias, células cancerígenas e na degradação de compostos orgânicos tóxicos. Este trabalho investigou a correlação entre as propriedades fotocrômicas e fotocatalíticas de fibras e dos filmes de TiO2, e de TiO2 dopados com H2WO4 e Na2WO4.2H2O. Para a síntese de fibras por electrospinning os reagentes utilizados foram: ácido acético glacial, propóxido de titânio, polivinilpirrolidona 10%, ácido túngstico e tungstato de sódio di hidratado. As fibras obtidas foram tratadas termicamente entre 650 ºC e 800 ºC, com patamar de 1 hora e taxa de aquecimento de 1,4 °C/min. Para obtenção dos filmes por spin-coater foram peparadas soluções contendo: 0,25 g de fibras tratadas entre 650 ºC e 800 ºC, etanol anidro, acetilacetona, Triton X-100 e polivinilbitiral. As amostras foram caracterizadas por difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e de transmissão (MET), análise termogravimétrica (TGA) e termo-diferencial (ATD), espectroscopia de reflectância difusa (ERD), perfilometria, teoria Brunnauer Emmet e Teller (BET), ensaios de degradação de 125 mL de uma solução 20 ppm do corante alaranjado de metila e colorimetria através do sistema CIELa*b*. Os melhores resultados foram obtidos com as amostras deTiO2∕Na2WO4.2H2O. Estas amostras foram mais eficientes na mineralização do corante alaranjado de metila, pois 3 das 4 amostras sintetizadas degradaram aproximadamente 100% do corante e simultaneamente expressaram os maiores valores de reflectância, possivelmente devido a existência de uma sincronização entre as características químicas e físicas destes óxidos e a formação de defeitos pontuais (vacâncias) que ocupam posições atômicas de rede. / The use of TiO2 as the most commonly used semiconductor in heterogeneous photocatalysis becomes relevant because of its efficiency in the decomposition of pollutants from water, air, bacteria, cancer cells and the degradation of toxic organic compounds. This work investigated the correlation between the photocatalytic and photocatalytic properties of TiO2 and TiO2 fibers and TiO2 doped with H2WO4 and Na2WO4.2H2O. For the synthesis of fibers by electrospinning the reagents used were: glacial acetic acid, titanium propoxide, 10% polyvinylpyrrolidone, tungstic acid and sodium tungstate dihydrate. The obtained fibers were heat treated between 650 °C and 800 °C, with a 1 hour threshold and a heating rate of 1.4 °C/min. To obtain the films by spin-coater were prepared solutions containing: 0.25 g of treated fibers between 650 ºC and 800 ºC, anhydrous ethanol, acetylacetone, Triton X-100 and polyvinylbutyral. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission (TEM), thermogravimetric (TGA) and thermo-differential analysis (DTA), diffuse reflectance spectroscopy (ERD), profilometry, Brunnauer Emmet and Teller (BET) theory, 125 ml degradation assays of a 20 ppm solution of methyl orange dye and colorimetry through the system CIELa*b*. The best results were obtained with TiO2/Na2WO4.2H2O samples. These samples were more efficient in the methyl orange dye mineralization, since 3 of the 4 synthesized samples degraded approximately 100% of the dye and simultaneously expressed the highest values of reflectance, possibly due to the existence of a synchronization between the chemical and physical characteristics of these oxides and the formation of point defects (vacancies) that occupy atomic network positions.

Os materiais CaWO4:TR3+, CaMoO4:TR3+, Ca(MO4):TR3+ (TR: Pr3+, Sm3+, Eu3+, Tb3+ e Dy3+) (M: W e Mo) foram preparados pelo método da coprecipitação acoplado ao método ultrassônico a fim de estudar suas aplicações em materiais fotônicos aplicados em LEDs. Após a reação de precipitação, o material foi filtrado sob pressão reduzida, lavado com água destilada, seco e armazenado em dessecador a vácuo. Esses materiais sem tratamento térmico se mostraram como pós brancos, de aspecto uniforme, cristalinos, não higroscópicos e insolúveis em solventes polares e apolares. Após a síntese, os materiais foram submetidos a tratamento térmico em forno resistivo (1000 &#176;C / 3 h) e sob radiação micro-ondas (5 min; ~1100 &#176;C e 22 min; ~1200 &#176;C). Este método oferece muitas vantagens se comparado aos métodos convencionais, tais como: método simples de operação, baixo custo, tempo curto de síntese e procedimento ambientalmente correto. Os materiais tratados sob altas temperaturas foram comparados com aqueles materiais sem tratamento térmico. Os materiais foram caracterizados pelas seguintes técnicas: espectroscopia de absorção no infravermelho (IV), análise termogravimetria (TG), difratometria de raios X - método do pó (DRX), microscopia eletrônica de varredura (MEV) e energia dispersiva de raios X (EDS). Os picos dentro do difratograma de raios X foram indexados na estrutura tetragonal scheelita I41/a. As propriedades fotoluminescentes dos compostos Ca(MO4) (M: W e Mo) dopados com Dy3+ e codopados com Eu3+ foram investigadas com base nas transições intraconfiguracionais 4f dos íons TR3+. Os espectros de excitação apresentaram bandas largas na região do UV, atribuídas às bandas de transferência de carga LMCT O&#8594;W; O&#8594;Mo e O&#8594;Eu3+. Os espectros de excitação dos fósforos dopados com Tb3+ apresentaram as bandas de absorção largas atribuídas à transferência de carga LMCT O&#8594;W6+ (5d) e O&#8594;Mo6+ (4d) sobrepostas às transições 4f8&#8594;4f75d1 do íon Tb3+ e também picos finos oriundos das transições 4f referentes aos íons Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8) e Dy3+ (4f9). O material CaWO4:Eu3+ submetido a tratamento térmico em forno resistivo (1000 &#176;C / 3 h) apresentou o fenômeno da luminescência persistente de cor vermelha. O material triplamente dopado CaWO4:Eu3+,Tb3+,Dy3+ apresentou cores ajustáveis, indo do branco quente ao branco frio, com grande potencial para aplicação em materiais fotônicos para iluminação no estado sólido. Também, os materiais CaWO4:Eu3+,Tb3+,Dy3+ e Ca(MO4):Dy3+,Eu3+ (M: W e Mo) foram montados a base de um polímero óptico de silicone e utilizando um LED de GaN de alta potência, gerando luz branca fria e quente de altas intensidades. As coordenadas CIE (Commission Internationale l\'Eclairage) sugerem emissões multicolores dos sistemas dopados com diferentes íons TR: Pr3+, Sm3+, Eu3+, Tb3+, Dy3+. Esses materiais se mostraram promissores em aplicação de materiais de iluminação do estado sólido, com a vantagem de serem preparados de forma rápida, em poucas etapas, com alto rendimento e serem ambientalmente amigáveis. / The materials CaWO4:TR3+, CaMoO4:TR3+, Ca(MO4):TR3+ (TR: Pr3+, Sm3+, Eu3+, Tb3+ e Dy3+) (M: W and Mo) were prepared by the coprecipitation and ultrasonic method in order to study their applications in photonic materials applied in LEDs. After the precipitation reaction, the material was filtered under reduced pressure, washed with distilled water, dried and stored in vacuum desiccator. These as prepared materials were shown to be white powders, uniform in appearance, crystalline, non-hygroscopic and insoluble in polar and apolar solvents. After the synthesis the materials were submitted to thermal treatment in resistive furnace (1000 &#176;C / 3 h) and also under microwave radiation (5 min; 1100 &#176;C e 22 min; 1200 &#176;C). This method offers many advantages compared to conventional methods, such as: simple operation method, low cost, brief synthesis time and environmentally correct procedure. The materials treated under high temperatures were compared with those materials without heat treatment. In the characterization of these phosphors, the following techniques were used: infrared (IR) absorption spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The X-ray diffraction peaks were indexed in the scheelite tetragonal structure. The photoluminescent properties of the compounds Ca(MO4) (M: W and Mo) Dy3+ doped and Eu3+ codoped were investigated based on the intraconfiguration transitions 4f of the TR3+ ions. Excitation spectra showed broad bands in the UV region attributed to the LMCT O &#8594; W charge transfer bands; O &#8594; Mo and O Eu3+. The excitation spectra of the phosphors doped with Tb3+ showed the wide absorption bands attributed to the charge transfer LMCT O2- (2p)W6+ (5d) and O2-(2p)Mo6+ (4d) overlapping the transitions 4f8&#8594;4f75d1 of Tb3+ ion and also fine peaks originating from the 4f transitions referring to ions Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8) and Dy3+ (4f9). The CaWO4:Eu3+ material submitted to thermal treatment in a resistive oven (1000 &#176;C / 3 h) exhibited the phenomenon of persistent red color luminescence. The triply-doped CaWO4:Eu3+,Tb3+,Dy3+ showed color matching, ranging from warm white to cool white, promising to be an excellent material to be applied in photonic materials for solid state lighting. Also, the materials CaWO4:Eu3+,Tb3+,Dy3+ and Ca(MO4):Dy3+,Eu3+ (M: W and Mo) were assembled on the basis of a silicone optical polymer and using a high power GaN LED, generating warm white and cold white light of high intensities. The CIE (Commission Internationale l\'Eclairage) coordinates suggest multicolored emissions of multicolor systems doped with various TR3+ ions: TR3+: Pr3+, Sm3+, Eu3+, Tb3+, Dy3+. These materials have proven to be promising in the application of solid state lighting materials, with the advantage of being quickly prepared, in a few steps, high performance and environmentally friendly.

Os materiais CaWO4:TR3+, CaMoO4:TR3+, Ca(MO4):TR3+ (TR: Pr3+, Sm3+, Eu3+, Tb3+ e Dy3+) (M: W e Mo) foram preparados pelo método da coprecipitação acoplado ao método ultrassônico a fim de estudar suas aplicações em materiais fotônicos aplicados em LEDs. Após a reação de precipitação, o material foi filtrado sob pressão reduzida, lavado com água destilada, seco e armazenado em dessecador a vácuo. Esses materiais sem tratamento térmico se mostraram como pós brancos, de aspecto uniforme, cristalinos, não higroscópicos e insolúveis em solventes polares e apolares. Após a síntese, os materiais foram submetidos a tratamento térmico em forno resistivo (1000 &#176;C / 3 h) e sob radiação micro-ondas (5 min; ~1100 &#176;C e 22 min; ~1200 &#176;C). Este método oferece muitas vantagens se comparado aos métodos convencionais, tais como: método simples de operação, baixo custo, tempo curto de síntese e procedimento ambientalmente correto. Os materiais tratados sob altas temperaturas foram comparados com aqueles materiais sem tratamento térmico. Os materiais foram caracterizados pelas seguintes técnicas: espectroscopia de absorção no infravermelho (IV), análise termogravimetria (TG), difratometria de raios X - método do pó (DRX), microscopia eletrônica de varredura (MEV) e energia dispersiva de raios X (EDS). Os picos dentro do difratograma de raios X foram indexados na estrutura tetragonal scheelita I41/a. As propriedades fotoluminescentes dos compostos Ca(MO4) (M: W e Mo) dopados com Dy3+ e codopados com Eu3+ foram investigadas com base nas transições intraconfiguracionais 4f dos íons TR3+. Os espectros de excitação apresentaram bandas largas na região do UV, atribuídas às bandas de transferência de carga LMCT O&#8594;W; O&#8594;Mo e O&#8594;Eu3+. Os espectros de excitação dos fósforos dopados com Tb3+ apresentaram as bandas de absorção largas atribuídas à transferência de carga LMCT O&#8594;W6+ (5d) e O&#8594;Mo6+ (4d) sobrepostas às transições 4f8&#8594;4f75d1 do íon Tb3+ e também picos finos oriundos das transições 4f referentes aos íons Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8) e Dy3+ (4f9). O material CaWO4:Eu3+ submetido a tratamento térmico em forno resistivo (1000 &#176;C / 3 h) apresentou o fenômeno da luminescência persistente de cor vermelha. O material triplamente dopado CaWO4:Eu3+,Tb3+,Dy3+ apresentou cores ajustáveis, indo do branco quente ao branco frio, com grande potencial para aplicação em materiais fotônicos para iluminação no estado sólido. Também, os materiais CaWO4:Eu3+,Tb3+,Dy3+ e Ca(MO4):Dy3+,Eu3+ (M: W e Mo) foram montados a base de um polímero óptico de silicone e utilizando um LED de GaN de alta potência, gerando luz branca fria e quente de altas intensidades. As coordenadas CIE (Commission Internationale l\'Eclairage) sugerem emissões multicolores dos sistemas dopados com diferentes íons TR: Pr3+, Sm3+, Eu3+, Tb3+, Dy3+. Esses materiais se mostraram promissores em aplicação de materiais de iluminação do estado sólido, com a vantagem de serem preparados de forma rápida, em poucas etapas, com alto rendimento e serem ambientalmente amigáveis. / The materials CaWO4:TR3+, CaMoO4:TR3+, Ca(MO4):TR3+ (TR: Pr3+, Sm3+, Eu3+, Tb3+ e Dy3+) (M: W and Mo) were prepared by the coprecipitation and ultrasonic method in order to study their applications in photonic materials applied in LEDs. After the precipitation reaction, the material was filtered under reduced pressure, washed with distilled water, dried and stored in vacuum desiccator. These as prepared materials were shown to be white powders, uniform in appearance, crystalline, non-hygroscopic and insoluble in polar and apolar solvents. After the synthesis the materials were submitted to thermal treatment in resistive furnace (1000 &#176;C / 3 h) and also under microwave radiation (5 min; 1100 &#176;C e 22 min; 1200 &#176;C). This method offers many advantages compared to conventional methods, such as: simple operation method, low cost, brief synthesis time and environmentally correct procedure. The materials treated under high temperatures were compared with those materials without heat treatment. In the characterization of these phosphors, the following techniques were used: infrared (IR) absorption spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The X-ray diffraction peaks were indexed in the scheelite tetragonal structure. The photoluminescent properties of the compounds Ca(MO4) (M: W and Mo) Dy3+ doped and Eu3+ codoped were investigated based on the intraconfiguration transitions 4f of the TR3+ ions. Excitation spectra showed broad bands in the UV region attributed to the LMCT O &#8594; W charge transfer bands; O &#8594; Mo and O Eu3+. The excitation spectra of the phosphors doped with Tb3+ showed the wide absorption bands attributed to the charge transfer LMCT O2- (2p)W6+ (5d) and O2-(2p)Mo6+ (4d) overlapping the transitions 4f8&#8594;4f75d1 of Tb3+ ion and also fine peaks originating from the 4f transitions referring to ions Pr3+ (4f2), Sm3+ (4f5), Eu3+ (4f6), Tb3+ (4f8) and Dy3+ (4f9). The CaWO4:Eu3+ material submitted to thermal treatment in a resistive oven (1000 &#176;C / 3 h) exhibited the phenomenon of persistent red color luminescence. The triply-doped CaWO4:Eu3+,Tb3+,Dy3+ showed color matching, ranging from warm white to cool white, promising to be an excellent material to be applied in photonic materials for solid state lighting. Also, the materials CaWO4:Eu3+,Tb3+,Dy3+ and Ca(MO4):Dy3+,Eu3+ (M: W and Mo) were assembled on the basis of a silicone optical polymer and using a high power GaN LED, generating warm white and cold white light of high intensities. The CIE (Commission Internationale l\'Eclairage) coordinates suggest multicolored emissions of multicolor systems doped with various TR3+ ions: TR3+: Pr3+, Sm3+, Eu3+, Tb3+, Dy3+. These materials have proven to be promising in the application of solid state lighting materials, with the advantage of being quickly prepared, in a few steps, high performance and environmentally friendly.

Thermal mismatch between different components of a system could be sources of problems like residual stress induced cracking, thermal fatigue or even optical misalignment in certain high technology applications. Use of materials with tailored thermal expansion coefficient is a counter-measure to overcome such problems. With its negative thermal expansion coefficient zirconium tungstate (ZrW2O8) is a candidate component to be used in synthesis of composites with controlled thermal expansion coefficient (CTE). ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and tungsten oxide at 1200oC. However, it has been demonstrated that ZrW2O8 can also be synthesized using wet chemical techniques, which provide a superior chemical homogeneity that often extents down to the atomic scale, and the convenient means of controlling nucleation and growth of the primary crystallites. With the commonly adopted wet chemical approaches, it is possible to crystallize particles with sizes in the submicrometer range at temperatures as low as 600 oC or even lower. In these studies, precursors are aged either below 100 oC (7 days &ndash / 3 weeks), or at 160-180 oC under hydrothermal conditions (1&ndash / 2 days). Besides the obvious disadvantage in the ageing steps, use of tungsten sources with high cost in all approaches, constitutes the other disadvantage. Production of composites with tunable controlled thermal expansion (CTE) has been achieved by blending negatively and positively expanding materials in different proportions. In majority of these studies composites have been produced by conventional sintering methods. Spark Plasma Sintering (SPS) is a recent technique / in which sintering can be achieved at relatively low temperatures in short durations. There is only one study made by Kanamori and coworkers on the use of SPS in sintering of a composite, in which ZrW2O8 is one of the constituents [1]. This study aims the synthesis of ZrW2O8 particles and composites that possess tunable or zero CTE. A novel precursor recipe for ZrW2O8 synthesis was developed. In preparation of the precursor a total of 2 days of ageing and a temperature less than 100 oC was used. It was developed using a cost-effective tungsten source, namely tungstic acid and its final pH was lower than 1. The particles obtained from &lsquo / unwashed&rsquo / procedure had sizes in micrometer range, while those obtained from &lsquo / washed&rsquo / case had sizes in the range of 400-600 nm. These precursors could readily be crystallized at 600 oC, which in turn provided the desired particle sizes for composite applications. Experimental details on the precursor development are hereby presented with a discussion on the effects of solution parameters (i.e. solubility of tungstic acid, adjustment of the stoichiometry, ageing time) on the phase purity of the fired product. Zirconium oxide (ZrO2) has positive vi thermal expansion, therefore ZrW2O8/ZrO2 was selected as the composite system, and for their synthesis both conventional and spark plasma sintering methods were experimented. Composition ranges that provide composites with almost zero CTE&rsquo / s were determined. The composite having a composition of containing 35% ZrW2O8, 65% ZrO2, and 35 w/o Al2O3 and sintered at 1200 oC for 24 hours had an expansion coefficient of 0.20 x 10-6/K for conventional method, while the one having a composition of 55% ZrW2O8, 45% ZrO2 and sintered at 1000 oC for 5 minutes had an expansion coefficient of 0.94 x 10-6/K for spark plasma sintering method. For characterization of the products X-ray diffraction (XRD), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), and thermal and dilatometer analyses (DTA/TGA/DMA) were used.

Many orchid species are seriously endangered at present. Reasons for their disappearing from natural habitats remain often unclear. Orchids depend on mycorrhizal symbiosis in nature, however only little is known about this symbiosis. Seeds of some species do not germinate in vitro, making their cultivation for scientific and rescue purposes impossible. We found that seed germination of one of such reluctant species, Pseudorchis albida, is strongly inhibited by nitrates even at extremely low concentrations. As this species prefers oligotrophic mountain meadows, nitrate-induced inhibition probably take place in natural conditions. Surprisingly, we found similar but slightly weaker inhibitory effect also in typical mesophillic species and even in slightly eutrophic ones. The sensitivity to nitrates correlates with trophy level of species canopy. This inhibitory effect of nitrates could be weakened by application of a range of growth regulators, including auxins, cytokinins and gibberellins, and also by mycorrhizal fungi. The action of nitratereductase is essential for this inhibitory effect of nitrates. Experiments with NO donors, scavengers, and NO quantification are pointing right at NO as compound which perhaps mediates nitrate inhibitory effect. Based on these results, the nitrate inhibitory...

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Les systèmes électrochromes suscitent un intérêt croissant dû au fait qu’ils permettent un contrôle des propriétés optiques dans le domaine du visible et du proche infrarouge.Lors d’une précédente étude, la synthèse d’électrolytes NaSICon (Na+ SuperIonicConductor) a été réalisée. Il est alors possible de développer des systèmes électrochromes « tout céramique » à mouvement de sodium par pulvérisation cathodique. Ce travail de thèse, s’articule autour de deux axes :Le premier concerne le développement de la contre-électrode du dispositif. Des films minces ont été synthétisés dans le système Na-W-O par pulvérisation de cibles Na2WO4. Le réglage de la pression de travail permet un contrôle du rapport Na/W. Il est alors possible de synthétiser des films nanocristallisés de NaxWO3+. Des caractérisations électrochimiques par voltampérométrie cyclique ont démontré la possibilité d’y insérer réversiblement du sodium. Il est alors envisageable d’utiliser ces composés comme couche électrochrome, et d’utiliser des films de WO3 épais comme contre-électrode.Le deuxième volet est l’étude d’électrodes conductrices transparentes d’oxyde de zinc dopé à l’aluminium (ZnO:Al). De fortes variations des propriétés de conduction électronique ont été observées. Les films les plus résistifs présentent une augmentation du paramètre c de la maille, et une faible mobilité des porteurs de charges en cohérence avec la présence de lacunes de zinc et une sur-stoechiométrie en oxygène. De plus, la structure électronique des films montre l’existence de deux coordinations différentes des atomes d’aluminium vis-à-vis de l’oxygène. Ces analyses suggèrent la formation d’une structure homologue (ZnO)mAl2O3 / Electrochromic systems are currently attracting increasing interest because they allow control of optical properties in the visible and near infrared. In a previous study, NaSICon (Na+ Super Ionic Conductor) electrolytes were synthesized as thin films by physical vapour deposition. It is therefore possible to develop an “all-ceramic” electrochromic system with sodium movement synthesized by magnetron sputtering. This work focuses on two resaerch areas:The first part concerns the development of the device’s counter electrode. Thin films were synthesized in the Na-W-O system by sputtering Na2WO4 targets. Adjustment of the work pressure allows the control of the Na/W ratio. Indeed, it is possible to synthesize nanocrystallized films of NaxWO3+ with x<1Electrochemical characterizations by voltamperometry showed the possibility to insert reversibly sodium. It is possible to use these compounds as electrochromic layer, and to use thick films of WO3 as counter electrode. The second part is the study of transparent conductive electrodes of aluminium doped zinc oxide (ZnO : Al). Strong variations of electronic conduction were observed. The most resistive films show on one hand an increase of the parameter c of the cell, and also a low mobility of charge carriers (optical measurements) consistent with the presence of zinc vacancies and oxygen over-stoichiometry. In addition the electronic structure of films, probed by XANES spectroscopy, shows the existence of two different coordinations of the aluminum atoms with oxygen. These observations suggest deterioration in the conductivity by the formation of a homologous structure (ZnO) mAl2O3

Materiais luminescentes contendo íons terras raras (TR3+) dopados nas matrizes de tungstatos [WO4]2- têm se mostrado excelentes candidatos como fósforos. Portanto, neste trabalho os materiais MWO4:TR3+ (M: Ca2+, Sr2+, Ba2+ e TR3+: Eu, Tb) foram preparados pelo método da coprecipitação com concentração de dopantes 0,1, 1,0, 5,0 e 10 % em mol. Este método comparado aos convencionais (cerâmico, combustão etc.), apresenta vantagens por ser um método simples de operação e rápido, baixo custo, preparado a temperatura ambiente, o processo de obtenção ambientalmente é correto e também produzem-se nanopartículas. Na caracterização destes fósforos foram utilizadas as técnicas: espectroscopia de absorção no infravermelho (IV), análise termogravimétrica (TG), difração de raios X - método do pó (DRX), microscopia eletrônica de varredura (MEV) e energia dispersiva de raios X (EDS). Os picos de difração de raios X foram indexados na estrutura tetragonal scheelita. Os fósforos dopados com Eu3+ e Tb3+ apresentaram cristalitos com dimensões nanométricas. Os estados de oxidação dos íons terras raras foram investigados com a espectroscopia de absorção de raios X com radiação Síncrotron (XANES), onde indicaram a presença apenas do estado trivalente para o európio nos materiais \"como preparados\" e calcinados. No entanto, foram detectados os estados trivalente e tetravalente do térbio dopado nas matrizes CaWO4 e BaWO4, calcinados à 500 ºC. As propriedades fotoluminescentes dos compostos foram investigadas com base nas transições intraconfiguracionais 4f6 (Eu3+) e 4f8 (Tb3+). Os espectros de excitação apresentaram bandas largas na região do UV, atribuídas às bandas de transferência de carga LMCT O&#8594;W e O&#8594;Eu3+. Os espectros de excitação dos fósforos MWO4:Tb3+ apresentaram as bandas de absorção largas atribuídas transferência de carga LMCT O2-(2p)&#8594;W6+(5d) sobrepostas às transições 4f8&#8594;4f75d e também picos finos oriundos das transições 4f8 do íon Tb3+. Ademais, os seus espectros de emissão exibiram bandas finas características das transições das 5D4&#8594;7FJ do íon térbio trivalente. Os valores altos do parâmetro de intensidade experimental (&#937;2 ~18 x 10-20 cm2) indicam que o sítio de simetria ocupado pelo íon Eu3+ dopado nas matrizes de tungstatos não apresentam caráter centrossimétrico, uma vez que os altos valores de &#937;2 são mais influenciados pelas pequenas mudanças angulares da geometria local do íon terra rara. Os valores de eficiência quântica de emissão &#951; do nível 5D0 dos fósforos MWO4:Eu3+ estão em torno de 30 %, sugerindo que não há variação significativa quando se altera os íons metálicos alcalinos terrosos. As coordenadas CIE (Commission Internationale l\'Eclairage) sugerem emissões multicolores dos sistemas MWO4:Eu3+ X mol-% que podem ser ajustáveis, em função das intensidades de emissão das bandas largas LMCT e dos picos finos das transições 5D0&#8594;7F0-4 e da concentração de dopagem (X mol-%) do íon Eu3+. Estes materiais luminescentes exibem cores de emissão vermelha, verde assim como cores intermediárias. / Luminescent materials containing rare earth ions (RE3 +) doped in [WO4]2- tungstate matrices have demonstrated excellent candidates as phosphors. Therefore, in this work the materials MWO4:TR3+ (M: Ca2+, Sr2+, Ba2+ e TR3+: Eu, Tb) were prepared by the coprecipitation method with doping concentration 0.1, 1.0, 5.0 and 10% mol. This method compared to conventional ones (ceramic, combustion, etc.), has advantages because it is a simple operation and fast, low cost, prepared at room temperature, the process of obtaining is environmentally correct and also make up the nanoparticles. The characterization techniques of these phosphors were investigated by infrared absorption spectroscopy (IR), thermogravimetric analysis (TG), X-ray diffraction patterns - powder method (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDS). The tungstate matrices doped with Eu3+ and Tb3+ showed crystallite sizes with nanometer dimensions. The rare earth oxidation states were investigated using absorption spectroscopy X-ray synchrotron radiation (XANES), which indicated the presence of only trivalent europium state materials \"as prepared\" and calcined. However, it was observed the trivalent and tetravalent state of terbium doped in CaWO4 and BaWO4 matrices, calcined at 500 º C. The photoluminescent properties of the compounds were investigated based on 4f6 (Eu3+) and 4f8 (Tb3+) intraconfigurational transitions. The excitation spectra showed broad bands in the UV region, assigned to the bands of charge transfer LMCT O&#8594;W e O&#8594;Eu3+. The excitation spectra of MWO4Tb3+ phosphors showed the broad absorption bands attributed charge transfer LMCT O2-(2p)&#8594;W6+(5d) overlapping with 4f8&#8594;4f75d transitions and narrow peaks arising from 4f8 transitions of Tb3+ ion. Moreover, their emission spectra exhibited narrow characteristic bands assigned to the 5D4&#8594;7FJ transitions of trivalent terbium ion. The high values of experimental intensity parameters (&#937;2 ~ 18 x 10-20 cm2) indicate that the site symmetry occupied by the Eu3+ ion doped in the tungstates matrix not present centrosymmetric character, since high values of &#937;2 are more affected by small angular changes of the local geometry around of rare earth ion. The values of emission quantum efficiencies (&#951;) of the 5D0 level MWO4:Eu3+ phosphors were at around 30%, suggesting that there is no significant variation when changing the alkaline earth metal ions. The CIE coordinates (Commission Internationale l\'Eclairage) data suggest multicolored emissions for the MWO4:Eu3+ X mol-% systems can be tuneable, which depending on the emission intensities of the LMCT broad bands and 5D0&#8594;7F0-4 narrow peaks and concentration doping (X mol-%) of the Eu3+ ion. These materials exhibit luminescent emissions with red, green and intermediate colors.

Ce travail présente les mesures de la polarisation par effet Compton du faisceau d'électrons de l'accélérateur TJNAF pour les expériences de mesure des facteurs de forme électromagnétiques du proton et de mesure des fonctions de réponse du nucléon dans la réaction de l'électroproduction de pion au voisinage de la résonance 6.(1232). Le polarimètre Compton, dont le principe repose sur la diffusion élastique électron-photon, a été conçu et réalisé autour d'une cavité Fabry-Perot de finesse élevée, de l'ordre de 25000. La puissance du laser incident, de type Nd:YAG à la longueur d'onde 1064 nm, est accumulée dans la cavité optique afin d'obtenir une luminosité d'interaction telle que la précision statistique sur la mesure de la polarisation des électrons atteigne 1% en une heure. La fréquence du laser est asservie par la méthode Pound-Drever à une fréquence de résonance de l'interféromètre. La polarisation circulaire du faisceau de photons dans la cavité a été mesurée égale à 99.6+/-0.45%. Cette grandeur, ainsi que la mesure de l'asymétrie expérimentale et du pouvoir d'analyse de notre instrument, intervient directement dans la mesure de la polarisation du faisceau d'électrons. Le pouvoir d'analyse a été déterminé par une caractérisation de la réponse du détecteur de photons, un calorimètre composé de 25 cristaux de PbW04, à l'aide des événements détectés en coïncidence avec le détecteur d'électrons, composé de 4 plans de 48 'pistes de silicium. Les incertitudes de mesure proviennent principalement de la modélisation de la fonction de réponse du détecteur, de l'effet d'empilement de la mesure de la polarisation des photons. L'incertitude relative totale sur la mesure de Pe est de 1.4% pour une prise de données de 40 minutes. Le polarimètre Compton permet aussi de mesurer les différences d'hélicité entre deux renversements de la polarisation des électrons. Celle ci a été trouvée compatible avec zéro à 0.3% près.