Ce travail de thèse porte sur l'étude des verres alumino-silicatés de calcium dopés à l'europium et le processus de leur cristallisation sous forme des vitrocéramiques dans le cadre de la recherche de nouveaux phosphores pour application LED à émission blanche. Nous avons étudié trois échantillons vitreux avec différentes teneurs en silice et avons élaboré des vitrocéramiques cristallisées. La caractérisation des verres et des vitrocéramiques a été réalisée par différentes techniques expérimentales : l'analyse thermique, la diffraction des rayons X et la spectroscopie de diffusion Raman. Les propriétés spectroscopiques de l'ion europium dans les verres et les vitrocéramiques synthétisés ont été étudiées. Le contrôle de la cristallisation des vitrocéramiques GC34 et GC50 par la diffraction des rayons X a permis d'identifier deux phases la mélilite et l'anorthite. Dans le cas de la vitrocéramique GC7, une seule phase alumino-calcique qui est la mayenite est cristallisée majoritairement. L'étude par la spectroscopie de diffusion Raman a permis d'une part, de suivre l'évolution de la cristallisation pendant les traitements thermiques en surface et en profondeur dans l'ensemble des vitrocéramiques. Nous avons montré que le processus de cristallisation a eu lieu en surface des échantillons et correspond typiquement à une nucléation hétérogène. D'autre part, une étude comparative avec des échantillons naturels analogues prise de la base de données RRUFF nous a permis de valider l'ensemble des résultats trouvés. Dans le cas des vitrocéramiques GC34 et GC50, les mesures des spectres d'émission et les durées de vie de l'ion Eu3+ montrent bien son incorporation dans les phases cristallines formées. L'ion Eu3+ tend à occuper seulement les sites Ca2+ (CN= 8) de la mélilite majoritaire dans la vitrocéramique GC34 alors, qu'il tend à s'incorporer dans les sites Ca2+ (CN= 6 et 7) et Ca2+ (CN=8) respectivement, des phases anorthite et mélilite formées dans la vitrocéramique GC50. Ces résultats ont été confirmés par les mesures d'affinement de raies. L'étude des spectres d'émission de l'ion Eu2+ a permis de mettre en évidence une modification de son environnement durant la cristallisation traduite par son incorporation dans les sites Ca2+ après réduction de l'ion Eu3+ pendant les recuits. Dans le cas de la vitrocéramique GC7, les spectres d'émissions et les mesures du déclin de luminescence de l'ion Eu3+ montrent bien que l'ion Eu3+ est incorporé dans la phase mayenite formée. En terme d'application, les mesures des coordonnées trichromatiques suggèrent que la dévitrification des verres semble être une technique efficace permettant d'obtenir de nouveaux matériaux luminophores (LED blanches) à émission intensifiée (cas des vitrocéramiques GC34 et G50) et accordable en modifiant leur composition et l'excitation / This work concerns the study of calcium aluminosilicate glass doped with europium and their process of crystallization as glass-ceramics as part of the search for new phosphors for white LED application. We studied three glass samples with different silica contents and have elaborated crystallized glass-ceramics. Characterization of glasses and glass-ceramics was performed by different experimental techniques: thermal analysis, X-ray diffraction and Raman spectroscopy. The spectroscopic properties of the europium ion in the glass and glass-ceramic synthesized were studied.Control of crystallization of GC34 and GC50 glass-ceramics by X-ray diffraction have been identified two phases, melilite and anorthite. In the case of the GC7 glass-ceramic, a single aluminum calcium phase, mayenite which crystallized predominantly. The study by Raman spectroscopy allowed to follow the evolution of the crystallization during heat treatment in the surface and of glass-ceramics. We have shown that the crystallization process initiate at the surface of the samples and corresponds typically to a heterogeneous nucleation. On the other hand, a comparison with similar natural samples allowed us to validate all the identifications.In the case of GC34 and GC50 glass-ceramics, emission spectra and lifetimes of Eu3+ ion clearly show its incorporation into the new-formed crystalline phases. The Eu3+ ion occupy the Ca2+ sites (CN = 8) in the major mélilite phase of the the GC34 glass-ceramic while, it incorporates the Ca2+ sites (CN = 6 and 7) and Ca2+ (CN = 8) of anorthite and mélilite phases formed in the GC50 glass-ceramic, respectively. These results were confirmed by Fluorescence Line Narrowing (FLN) measurements. The study of emission spectra of the Eu2+ ion allowed highlighting changes during crystallization associated with the reduction of the Eu3+ ions during annealing. In the case of the low silicate GC7 glass-ceramic, emission spectra and lifetimes measurements of the Eu3+ ion show that the Eu3+ ions are incorporated into the mayenite phase. In terms of application, the analyses of the trichromatic coordinates suggest that the glass devitrification appears to be an efficient technique to achieve new white LED phosphor materials with intensified (mainly for GC34 and G50 glass-ceramics) and tunable emission by varying composition and/or excitation

A project studied wetting of iron, nickel and platinum by molten MnO-SiO2 (MS) and CaO-Al2O3-SiO2 (CAS) slags of eutectic composition to contribute to understanding of wetting behaviour of solid metal-molten oxide systems relevant to steelmaking. Novel results of dynamic wetting behaviour by the sessile drop method were obtained under strongly reducing atmosphere (oxygen partial pressure 10-20 -- 10-18 atm). Terminal contact angles (after 240 min) for MS slag were: for iron substrates -5??2??(1350??C), 9+-2?? (1390??C), 6+-2 (1450??C); nickel -- 3+-2??(1350 and 1390??C); and platinum --15+-2??(1350 and 1390??C), 12+-2??(1450??C). Contact angles with CAS slag were: iron -- 55+-2??(1350??C), 60+-2?? (1390??C), 44+-2?? (1450??C); nickel -- 59+-2??(1350??C), 60+-2?? (1390??C); and platinum -- 15+-2?? (1350, 1390 and 1450??C). Values for interfacial tension, work of adhesion, spreading parameter (S) and interaction coefficient (Ф) were also determined. Work of adhesion for all three substrates with MS slag changed in a very narrow range 910 - 930 mJ/m2. Interfacial tension with this slag was 1,480 mN/m for Ni at 1350-1390??C, and 1,880-1,890 mN/m for Pt in the temperature range 1,350-1,450??C. For iron, interfacial tension was 1,720 mN/m at 1350??C (γ-Fe); it decreased to 1590-1580 mN/m with increasing temperature to 1390 and 1450??C (-Fe). Lower work of adhesion and higher interfacial tension was found for metals with CAS slag. Wetting properties of Pt substrate with MS slag were close to that with CAS slag, while Fe and Ni substrates showed better wetting by MS slag in comparison with CAS slag. This was attributed to higher reactivity of Fe and Ni with MS slag, particularly reduction of MnO. Although MnO was also reduced in reaction with Pt, oxygen adsorption in contact with both slags was a major factor governing wettability of Pt. Dissolution of manganese in nickel and platinum substrates at elevated temperatures modified the interface chemistry, causing formation of a liquid alloy phase. Degree of silica reduction from MS slag was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS slag. Concentration profiles of Mn and Si across the interface and along the metal surface were used to estimate diffusion coefficients. Diffusion along metal surfaces was generally higher by 1 to 2 orders of magnitude than across the interface. Reduction of oxides and adsorption of oxygen modify the metal-oxide interface, making wetting dynamic. They have a profound on interfacial properties.

A project studied wetting of iron, nickel and platinum by molten MnO-SiO2 (MS) and CaO-Al2O3-SiO2 (CAS) slags of eutectic composition to contribute to understanding of wetting behaviour of solid metal-molten oxide systems relevant to steelmaking. Novel results of dynamic wetting behaviour by the sessile drop method were obtained under strongly reducing atmosphere (oxygen partial pressure 10-20 -- 10-18 atm). Terminal contact angles (after 240 min) for MS slag were: for iron substrates -5??2??(1350??C), 9+-2?? (1390??C), 6+-2 (1450??C); nickel -- 3+-2??(1350 and 1390??C); and platinum --15+-2??(1350 and 1390??C), 12+-2??(1450??C). Contact angles with CAS slag were: iron -- 55+-2??(1350??C), 60+-2?? (1390??C), 44+-2?? (1450??C); nickel -- 59+-2??(1350??C), 60+-2?? (1390??C); and platinum -- 15+-2?? (1350, 1390 and 1450??C). Values for interfacial tension, work of adhesion, spreading parameter (S) and interaction coefficient (Ф) were also determined. Work of adhesion for all three substrates with MS slag changed in a very narrow range 910 - 930 mJ/m2. Interfacial tension with this slag was 1,480 mN/m for Ni at 1350-1390??C, and 1,880-1,890 mN/m for Pt in the temperature range 1,350-1,450??C. For iron, interfacial tension was 1,720 mN/m at 1350??C (γ-Fe); it decreased to 1590-1580 mN/m with increasing temperature to 1390 and 1450??C (-Fe). Lower work of adhesion and higher interfacial tension was found for metals with CAS slag. Wetting properties of Pt substrate with MS slag were close to that with CAS slag, while Fe and Ni substrates showed better wetting by MS slag in comparison with CAS slag. This was attributed to higher reactivity of Fe and Ni with MS slag, particularly reduction of MnO. Although MnO was also reduced in reaction with Pt, oxygen adsorption in contact with both slags was a major factor governing wettability of Pt. Dissolution of manganese in nickel and platinum substrates at elevated temperatures modified the interface chemistry, causing formation of a liquid alloy phase. Degree of silica reduction from MS slag was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS slag. Concentration profiles of Mn and Si across the interface and along the metal surface were used to estimate diffusion coefficients. Diffusion along metal surfaces was generally higher by 1 to 2 orders of magnitude than across the interface. Reduction of oxides and adsorption of oxygen modify the metal-oxide interface, making wetting dynamic. They have a profound on interfacial properties.

Ce travail a pour but d'étudier les propriétés structurales et dynamiques des verres aluminosilicate de calcium CaO-Al2O3-SiO2 (CAS) par dynamique moléculaire classique, à partir d'un potentiel empirique de type Born-Mayer-Huggins, construit sur la base de résultats de dynamique moléculaire ab initio (AIMD) et expérimentaux. Il montre de bonnes propriétés de transférabilité sur toutes les concentrations pour les propriétés structurales et dynamiques étudiées. L'évolution des propriétés structurales a été étudiée en fonction de la température et de la concentration en silice pour trois rapports de concentrations R = [CaO]/[Al2O3]= 1, 1.57 et 3. Les résultats révèlent la présence d'oxygènes non-pontants et tricoordonnés et d'aluminium penta-coordonnés pour toutes les concentrations dont le nombre diminue avec l'augmentation avec la concentration en silice. L'étude de la viscosité et du temps de relaxation structural avec la température a permis de montrer que la fragilité diminue avec l'augmentation de la concentration en silice pour les trois valeurs de R. Une corrélation avec l'évolution des oxygènes non pontant indique que ces derniers jouent un rôle prépondérant pour la fragilité. Il est montré que la théorie des couplages de modes s'applique à la dynamique des CAS et qu'une violation de la relation de Stokes-Einstein se produit au-dessus du point de fusion expérimental indiquant une hétérogénéité dynamique. / The aim of this work is to study the structural and dynamic properties of calcium aluminosilicate glasses CaO-Al2O3-SiO2 (CAS) by classical molecular dynamics, using an empirical potential of the Born-Mayer-Huggins type, built on the basis of ab initio molecular dynamics (AIMD) and the experimental results. This potential proves to be transferable for all concentration and the structural and dynamic properties studied. The evolution of structural properties has been studied as a function of temperature and silica content for the three concentration ratios R = [CaO]/[Al2O3]= 1, 1.57 et 3. The results reveal the presence of non-bonding oxygen, oxygen triclusters and AlO5 structural units for all the concentrations whose number decrease with increasing silica content. The study of the temperature evolution of the viscosity and structural relaxation time shows that the fragility decreases with the increase of silica content for all values of R. A correlation with the evolution of the number non-bonding oxygen indicates that they play a preponderant role for the fragility. It is shown that the mode coupling theory can be applied to the dynamics of the CAS and that a violation of the Stokes-Einstein relation occurs well above the experimental melting point indicating a dynamical heterogeneity. Keywords: calcium aluminosilicate, diffusion, viscosity, fragility, BMH potential, molecular dynamics, dynamical heterogeneity, non-bonding oxygen.

Apresentamos uma série de novos resultados acerca dos vidros aluminosilicato de cálcio com diferentes concentrações de sílica (7,0 e 34,0% em massa) dopados com o íon Tb3+ (Tb4O7 = 0,05 - 15,0% em massa). A partir de medidas de absorção, excitação, emissão e tempos de decaimento; discutimos detalhadamente os mecanismos de emissão verde e azul do Tb3+ neste sistema vítreo. As emissões na região do azul (nível 5D3) foram analisadas tanto pela excitação direta no UV (emissão de Stokes) quanto por conversão ascendente de energia (emissão anti-Stokes), após a excitação em 488 nm (excitação ressonante com o nível 5D4). Para excitação em 325 nm, verificou-se que a intensidade da luminescência verde aumenta linearmente com a concentração, enquanto a emissão azul é fortemente reduzida com o aumento da concentração de Tb3+. No caso da excitação em 488 nm, observou-se uma forte saturação das emissões no verde, para intensidades duas ordens de grandeza menores que o esperado (Isat = 2,3×106 W/cm2). Por meio de um sistema de equações de taxa, mostramos que esse comportamento pode ser explicado pelo mecanismo de absorção do estado excitado e por uma seção de choque de absorção (5D4 → 5D3) aproximadamente duas ordens de magnitude maior do que a observada na transição 7F6 → 5D4. Espectros de excitação e emissão realizados a baixa temperatura (6 K) evidenciaram a presença de emissões atribuídas à matriz hospedeira. Medidas de Z-scan resolvidas no tempo, com excitação em 488 nm também foram realizadas e nos permitiram calcular a variação da polarizabilidade (Δαp) das amostras. A concentração de sílica apresentou forte influência nas propriedades não lineares aferidas. Para a amostra com menor concentração de sílica (7,0% em massa), o valor de Δαp é aproximadamente 10 vezes maior do que para a amostra com maior concentração de sílica (34% em massa). / We present a series of new results concerning Tb+3 (Tb4O7 = 0,05 - 15,0 wt.%) doped calcium aluminosilicate glasses with different silica concentrations (7.0 and 34.0 wt.%). Through optical absorption, excitation spectra, photoluminescence, and fluorescence decay measurements, the blue and green Tb+3 emission are discussed in detail. Emissions in the UV-blue region (5D3 level) were analyzed by direct UV excitation (Stokes emission) and by upconversion (anti-Stokes emission), resonant excitation with level 5D4 level. For the excitation at 325 nm, the intensity of the green luminescence increases linearly with the Tb+3 concentration. In opposite, the blue emission is strongly reduced with increasing the Tb+3 concentration from 0.5 to 15.0% (wt%). In the case of the 488 nm excitation, strong saturation of the green emissions was observed for pump intensity two orders of magnitude lower than expected (Isat = 2,3×106 W/cm2). By means a rate equations system, we explain this behavior by the excited state absorption and by an absorption cross section (5D4 → 5D3) approximately two orders of magnitude larger than 7F6 → 5D4 transition. Excitation and emission spectra were performed at low temperature (6 K) in the Tb doped LSCAS glass. These spectra showed matrix emission bands. Time-resolved Z-scan measurements were performed (at 488 nm). From these measurements, we determine the polarizability change (Δαp) in Tb doped glasses. The silica concentration presents a great influence on the nonlinear properties measured. The Δαp value in low silica calcium aluminosilicate glass (7.0 wt.%) is approximately 10 times higher than the value determined the sample with a higher silica content (34.0 wt.%).

A busca por alternativas viáveis de produção de energia limpa e renovável, utilizando recursos naturais, tem sido um grande desafio. Em especial, o interesse no uso da energia solar para obter energia elétrica tem aumentado. Todavia, as células solares convencionais que são confeccionadas a partir de silício cristalino (Si-c) apresentam uma eficiência de conversão limitada, principalmente, devido às perdas por incompatibilidade espectral. Sendo assim, um dos objetivos dos pesquisadores na área de fotovoltaicos tem sido converter eficientemente fótons da região do visível do espectro solar para a região do infravermelho, onde a célula solar de Si-c possui maior eficiência. A eficiência desta conversão poderia ser melhorada de 28% até 40% usando conversores de energia compostos por íons terras raras. Neste trabalho foram estudadas as propriedades espectroscópicas dos íons terras raras Térbio (Tb3+) e Itérbio (Yb3+), embebidos em três diferentes materiais: vidro aluminosilicato de cálcio com baixa concentração de sílica (7%) (LSCAS), vidro tetraborato de cálcio-lítio (Calibo) e nano-cristais de óxido de zircônia (ZrO2). Sendo assim, nossos estudos visam elucidar os mecanismos geradores dos processos de conversão ascendente e descendente de energia. No processo de conversão ascendente de energia há conversão dos fótons de excitação de baixa energia na região do infravermelho em fótons de alta energia na região do visível. Por outro lado, no processo de conversão descendente de energia ocorre a conversão dos fótons de excitação de alta energia na região do ultravioleta/visível em um ou mais fótons de baixa energia na região do infravermelho. As propriedades espectroscópicas dos materiais estudados foram discutidas a partir das medidas de absorção, luminescência, excitação, evolução temporal da luminescência, curva de potência, difração de raios-X, X-Ray Absorption Near Edge Structure e ressonância paramagnética eletrônica, em função da concentração dos íons Tb3+ e Yb3+. Os resultados mostraram que todas as amostras apresentam conversão ascendente de energia. Assim como, em todas as amostras ocorre o processo de conversão descendente de energia. Em ambos os processos foram identificados os mecanismos geradores dos mesmos. Estes resultados mostram um avanço nos estudos dos processos de conversão ascendente e descendente de energia em sistemas co-dopados com íons Tb3+ e Yb3+. Os resultados sugerem que os materiais estudados podem ser empregados para aumentar a eficiência de conversão da célula solar de Si-c via conversão descendente de energia. / The search for possible alternatives to produce clean and renewable energy using the natural resources has been a great challenge. In particular, the interest to use the solar energy to produce electricity has been increased. However, crystalline silicon-based (c-Si) conventional solar cells have limited conversion efficiency, mainly due to spectral mismatch losses. Thus, one of the goals of some researchers in the photovoltaic field has been to efficiently convert photons in the visible region of the solar spectrum to the infrared region, where the c-Si solar cell has its higher efficiency. The efficiency of this conversion could be enhanced from 28% up to 40% using energy converters based on rare-earths ions. In this work, the spectroscopic properties of rare earth ions, such as Terbium (Tb3+) and Ytterbium (Yb3+) embedded in three different materials were studied: low- silica calcium aluminosilicate glass (7%) (LSCAS), lithium calcium tetraborate glass (Calibo) and zirconium oxide nano-crystals (ZrO2). Thus, our studies aimed to elucidate the mechanisms that generate the Up-conversion and Down-conversion processes. In the Up-conversion process, there is the conversion of the low-energy excitation photons in the near-infrared to high-energy photons in the visible. On the other hand, in the Down-conversion process there is the conversion of the high-energy excitation photons in the ultraviolet/visible region to low-energy photons in the near-infrared region. The optical properties of the studied materials were discussed through absorption, luminescence, excitation, temporal evolution of the luminescence, power curve, X-ray diffraction, X-Ray Absorption Near Edge Structure and electron paramagnetic resonance measurements, as a function of the concentration of Tb3+ and Yb3+ ions. The results showed that all samples exhibit Up-conversion process. In addition, in all samples occurs the Down-conversion process. In both processes were identified the mechanisms that produce them. These results show a breakthrough in the studies of the Up-conversion and Down-conversion processes in Tb3+ and Yb3+ co-doped systems. The results suggest that the materials are applicable in enhancing the conversion efficiency of the Si-c solar cell via NIR Down-conversion.

L’objectif de ce travail de thèse est d’établir les relations entre les propriétés structurales et les conditions d’élaboration d’un vitrifiat de déchets amiantés (nom commercial Cofalit®), dans la perspective de fabriquer un prototype de module de stockage thermique d’énergie solaire. Malgré des provenances de déchets très diverses, les variations de compositions du vitrifiat restent limitées. Les conditions d’élaboration (de refroidissement en particulier) induisent par contre d’importantes disparités dans la microstructure. L’analyse d’une carotte de Cofalit nous a permis de déterminer les mécanismes de cristallisation lors de la fabrication du Cofalit (refroidissement non contrôlé), conduisant à un mélange de phases cristallisées et vitreuse. Nous avons étudié les propriétés structurales (par DRX et RMN) et de cristallisation d’échantillons modèles représentatifs du matériau industriel. Les variations de composition observées sur celui-ci ont été simulées par des ajouts de silice ou de chaux. L’influence de la teneur en fer sur les propriétés radiatives, structurales (verres et céramiques) et de cristallisation a également été quantifiée. Le suivi de la cristallisation séquentielle des céramiques a été effectué par DRX in situ à haute température, à partir de l’état vitreux et à partir de l’état liquide lors du refroidissement. Ces essais ont montré que le Cofalit cristallise complètement pour des vitesses de refroidissement inférieures à 10 K/min. La stabilité du Cofalit (au niveau structural) lors de recuits à hautes températures a également été démontrée. / The aim of this work is to establish relationships between structural properties and production conditions of a vitrified asbestos-containing wastes ceramics (commercially named Cofalit®), with the goal of elaborating a prototype for thermal energy storage of solar energy. Despite various waste sources, the variations of composition observed for this material are limited. On the contrary, the production conditions (cooling stage in particular) induce important differences in the material microstructure. The analysis of a Cofalit core sample allowed us to determine the crystallisation mechanisms during its fabrication process (uncontrolled cooling), leading to a mixture of vitreous and crystalline phases. We propose a structural study (by XRD and NMR) and crystallization properties analyses of synthetic samples, representative of the industrial material. Observed variations of composition on the latter are simulated by additions of silica and lime. The influence of iron oxide content on radiative, structural and crystallization properties (of both glass and ceramic samples) have also been investigated. The following of the sequential crystallisation of ceramic samples has finally been performed using in situ high temperature XRD, from glassy state and during cooling from liquid state. These tests show that the Cofalit crystallizes completely for rates lower than 10 K/min. The high temperature stability on a structural level has also been demonstrated during annealings.

A busca por alternativas viáveis de produção de energia limpa e renovável, utilizando recursos naturais, tem sido um grande desafio. Em especial, o interesse no uso da energia solar para obter energia elétrica tem aumentado. Todavia, as células solares convencionais que são confeccionadas a partir de silício cristalino (Si-c) apresentam uma eficiência de conversão limitada, principalmente, devido às perdas por incompatibilidade espectral. Sendo assim, um dos objetivos dos pesquisadores na área de fotovoltaicos tem sido converter eficientemente fótons da região do visível do espectro solar para a região do infravermelho, onde a célula solar de Si-c possui maior eficiência. A eficiência desta conversão poderia ser melhorada de 28% até 40% usando conversores de energia compostos por íons terras raras. Neste trabalho foram estudadas as propriedades espectroscópicas dos íons terras raras Térbio (Tb3+) e Itérbio (Yb3+), embebidos em três diferentes materiais: vidro aluminosilicato de cálcio com baixa concentração de sílica (7%) (LSCAS), vidro tetraborato de cálcio-lítio (Calibo) e nano-cristais de óxido de zircônia (ZrO2). Sendo assim, nossos estudos visam elucidar os mecanismos geradores dos processos de conversão ascendente e descendente de energia. No processo de conversão ascendente de energia há conversão dos fótons de excitação de baixa energia na região do infravermelho em fótons de alta energia na região do visível. Por outro lado, no processo de conversão descendente de energia ocorre a conversão dos fótons de excitação de alta energia na região do ultravioleta/visível em um ou mais fótons de baixa energia na região do infravermelho. As propriedades espectroscópicas dos materiais estudados foram discutidas a partir das medidas de absorção, luminescência, excitação, evolução temporal da luminescência, curva de potência, difração de raios-X, X-Ray Absorption Near Edge Structure e ressonância paramagnética eletrônica, em função da concentração dos íons Tb3+ e Yb3+. Os resultados mostraram que todas as amostras apresentam conversão ascendente de energia. Assim como, em todas as amostras ocorre o processo de conversão descendente de energia. Em ambos os processos foram identificados os mecanismos geradores dos mesmos. Estes resultados mostram um avanço nos estudos dos processos de conversão ascendente e descendente de energia em sistemas co-dopados com íons Tb3+ e Yb3+. Os resultados sugerem que os materiais estudados podem ser empregados para aumentar a eficiência de conversão da célula solar de Si-c via conversão descendente de energia. / The search for possible alternatives to produce clean and renewable energy using the natural resources has been a great challenge. In particular, the interest to use the solar energy to produce electricity has been increased. However, crystalline silicon-based (c-Si) conventional solar cells have limited conversion efficiency, mainly due to spectral mismatch losses. Thus, one of the goals of some researchers in the photovoltaic field has been to efficiently convert photons in the visible region of the solar spectrum to the infrared region, where the c-Si solar cell has its higher efficiency. The efficiency of this conversion could be enhanced from 28% up to 40% using energy converters based on rare-earths ions. In this work, the spectroscopic properties of rare earth ions, such as Terbium (Tb3+) and Ytterbium (Yb3+) embedded in three different materials were studied: low- silica calcium aluminosilicate glass (7%) (LSCAS), lithium calcium tetraborate glass (Calibo) and zirconium oxide nano-crystals (ZrO2). Thus, our studies aimed to elucidate the mechanisms that generate the Up-conversion and Down-conversion processes. In the Up-conversion process, there is the conversion of the low-energy excitation photons in the near-infrared to high-energy photons in the visible. On the other hand, in the Down-conversion process there is the conversion of the high-energy excitation photons in the ultraviolet/visible region to low-energy photons in the near-infrared region. The optical properties of the studied materials were discussed through absorption, luminescence, excitation, temporal evolution of the luminescence, power curve, X-ray diffraction, X-Ray Absorption Near Edge Structure and electron paramagnetic resonance measurements, as a function of the concentration of Tb3+ and Yb3+ ions. The results showed that all samples exhibit Up-conversion process. In addition, in all samples occurs the Down-conversion process. In both processes were identified the mechanisms that produce them. These results show a breakthrough in the studies of the Up-conversion and Down-conversion processes in Tb3+ and Yb3+ co-doped systems. The results suggest that the materials are applicable in enhancing the conversion efficiency of the Si-c solar cell via NIR Down-conversion.