Un verre de composition 67 % SiO_2 - 12 % Al_2O_3 - 21 % CaO, choisi comme modèle simplifié des pellicules d'altération, est modélisé par les méthodes de dynamique moléculaire (DM) classique et ab initio.<br /><br />L'étude des effets de taille, en DM classique, montre que les systèmes de 100 atomes présentent un caractère plus ordonné par rapport à des systèmes de plus grande taille. L'effet observé est principalement lié à l'utilisation de termes de potentiels 3-corps. Non observable sur les facteurs de structure neutronique, le facteur calculé à partir d'une structure modélisée est en bonne adéquation avec une mesure expérimentale et valide le modèle classique. Les structures modélisées présentent un excès d'atomes d'oxygènes non pontants qui peuvent être compensés par des atomes d'oxygène tricoordonnés. L'exclusion non totale des atomes aluminium est aussi mis en évidence.<br /><br />La poursuite de la dynamique en DM ab initio de systèmes de 100 et 200 atomes fabriqué en DM classique permet d'affiner localement les structures (distances interatomiques, angles). Une description plus réaliste des vibrations est obtenue.<br /><br />La modélisation de films minces en DM classique montre une zone enrichie en calcium en sub-surface où l'on observe une dépolymérisation du réseau vitreux. L'aluminium s'étend le plus en surface et s'y trouve tricoordonné. La distribution atomique des films et les entités AlO_3 sont confirmés par un ajustement en DM ab initio. En DM classique, les atomes d'aluminium produisent un fort champ électrique au dessus de la surface et ils constituent, avec les sites NBO-Ca, des zones réactives avec H_2O.

Nous avons étudié les effets de l'irradiation ionisante (e¯- et γ-) sur les propriétés luminescentes des ions Yb3+ et Er3+ dans des verres aluminosilicates (AS) et phosphates en essayant de comprendre l'impact de l'environnement initial de Yb3+ et surtout le rôle des clusters d'Yb. Pour cela, des verres AS et phosphates contenant les quantités différentes de clusters d'Yb ont été irradiés à des doses comprises entre 104 et 2∙109 Gy. Nous avons montré que la relaxation des défauts ponctuels est ralentie en présence de clusters d'Yb dans le verre. La quantité de défauts ponctuels en fonction du lg(dose) est stable aux faibles doses puis décrit une courbe en cloche. La présence des clusters d'Yb limite la production de défauts aux doses élevées, quelle que soit la composition du verre (AS ou phosphate).En conséquence, la variation de la durée de vie de l'état excité 2F5/2 en fonction du log de la dose décrit deux régions. Pour un fort contenu de cluster d'Yb, la durée de vie diminue linéairement avec le log de la dose. Ce résultat ne dépend pas du type de verre, ni de la nature de l'élément terre rare (Er3+). Ceci signifie qu'il existe un mécanisme plus général n'impliquant pas un 'un type de défaut particulier. De plus, la complexité du signal RPE dû aux défauts ponctuels dans les verres phosphates a été interprétée grâce à la forte évolution de celui-ci en fonction de la composition du verre, de la dose et du temps. Au moins 8 défauts ponctuels paramagnétiques ont été identifiés ainsi qu'un défaut diamagnétique luminescent dont l'origine est discutée.

Made available in DSpace on 2014-12-17T14:07:01Z (GMT). No. of bitstreams: 1 MartaLPS_partes_autorizadas_pelo autor.pdf: 1296900 bytes, checksum: ae142b4d715f0718971945acd4c853ad (MD5) Previous issue date: 2009-06-01 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The mesoporous molecular sieves of MCM-41 and AlMCM-41 type are considered as promising support for metal in the refining processes of petroleum-based materials as catalysts and adsorbents for environmental protection. In this work the molecular sieves MCM-41 and AlMCM-41 were synthesized by replacing the source of silica conventionally used, for quartz, an alternative and abundant, and the use of waste from the production of diatomaceous earth, an aluminum-silicate, as a source aluminum, due to abundant reserves of diatomaceous earth in the state of Rio Grande do Norte in the city of Cear?-Mirim, with the objective of producing high-value materials that have similar characteristics to traditional commercial catalysts in the market. These materials were synthesized by the method of hydrothermal synthesis at 100 ? C for 7 days and subjected to calcination at 500 ? C for 2 hours under flow of nitrogen and air. The molecular sieves were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TG), adsorption of N2 (BET and BJH methods), spectroscopy in the infra red (FTIR), microscopy scanning electron (SEM) and transmission electron microscopy (TEM). The analysis indicated that the synthesized materials showed characteristic hexagonal structure of mesopores materials with high specific surface area and sort and narrow distribution of size of pores / As peneiras moleculares mesoporosas do tipo MCM-41 e AlMCM-41 s?o consideradas promissoras como suporte para metais em processos de refino de materiais a base de petr?leo, como catalisadores e como adsorventes para prote??o ambiental. Neste trabalho foram sintetizadas as peneiras moleculares MCM-41 e AlMCM-41 atrav?s da substitui??o da fonte de s?lica convencionalmente utilizada, por quartzo, uma fonte alternativa e abundante, e pela utiliza??o do rejeito da produ??o de diatomita, um alumino-silicato, como fonte de alum?nio, devido a abundante reserva de diatomita no estado do Rio Grande do Norte, no munic?pio de Cear?-Mirim, com o objetivo de produzir materiais de alto valor agregado que apresentam caracter?sticas semelhantes aos catalisadores comerciais tradicionalmente existentes no mercado. Estes materiais foram sintetizados pelo m?todo de s?ntese hidrot?rmica a 100 ?C por 7 dias, e submetidos a calcina??o a 500 ?C por 2 horas sob fluxo de nitrog?nio e ar. As peneiras moleculares foram caracterizadas por difra??o de raios-X (DRX), an?lises t?rmicas diferencial (DTA) e termogravim?trica (TG), fisissor??o de N2, (M?todos de BET e BJH), espectroscopia na regi?o do infra vermelho (FTIR), microscopia eletr?nica de varredura (MEV) e microscopia eletr?nica de transmiss?o (MET). As an?lises indicaram que os materiais sintetizados apresentaram estrutura hexagonal caracter?stica dos materiais mesoporosos, com elevadas ordena??o e ?rea superficial espec?fica e estreita distribui??o de tamanho de poros

Cette thèse porte sur l’étude du processus de cristallisation de verres et l’élaboration de vitrocéramiques transparentes dans le visible. Ce travail a permis d’élaborer plusieurs vitrocéramiques complètement cristallisées et transparentes, ce qui constitue un résultat exceptionnel pour ce type de matériaux qui perd habituellement la transparence lors de la cristallisation. Ces matériaux originaux et novateurs ont fait l’objet d’un brevet sur des "Céramiques transparentes" (dépôt en France N° 1161025 et extension internationale PCT N° EP2012/074171) et de plusieurs articles (cf. page 162). Plusieurs verres dans les systèmes oxydes de terres rares-oxydes d’alcalino-terreux-Al2O3-SiO2 ont été élaborés au moyen d’un lévitateur aérodynamique couple a un chauffage par laser puis étudiés. Une recherche de la composition optimale du verre d’aluminosilicate d’yttrium parent qui permettrait d’avoir un maximum de cristaux de YAG sans formation d’impuretés lors de la cristallisation a été menée. L’étude de la cristallisation du YAG a partir des verres d’aluminosilicates d’yttrium choisis, réalisée principalement par RMN et diffraction des rayons X, a montré que les ions de silicium initialement présents dans la matrice vitreuse se trouvent incorporés dans les cristaux de YAG formes, en substitution des ions d’aluminium des sites tétraédriques. Les conséquences structurales de cette incorporation dans le YAG ont été étudiées. En particulier, la réduction de la maille cubique du YAG et des liaisons des sites tétraédriques a été mise en évidence par DRX et affinement Rietveld. Par RMN, la présence d’aluminium en coordinence IV, V et VI a été détectée dans le verre parent. Pour ce système, il est remarquable que la cristallisation du verre d’aluminate d’yttrium puisse avoir lieu au-dessous de sa température de transition vitreuse. Ce phénomène rarement rapporté pourrait être expliqué par la tendance élevée du verre à cristalliser et par la capacité de Si4+ à s’incorporer dans les cristaux de YAG comme cette étude le démontre. L’avancement de la cristallisation par recuit du verre au-dessous de Tg a été suivi ainsi que l’absorbance et la diffusion de l’irradiation IR par les vitrocéramiques en se basant sur le modèle de Rayleigh-Guns-Debye. Cette étude a révélé l’influence de la différence de l’indice de réfraction entre le verre et les cristaux sur la diffusion de la lumière. Les images MET et MEB de ces vitrocéramiques montrent des cristaux de YAG de tailles comprises entre 500 nm et 1300 nm. La cristallisation d’une autre famille de verres de terres rares a été étudiée. Il s’agit de verres d’aluminate de lanthane et de borate de lanthane. Dans les deux cas, une cristallisation démarrant à partir de la surface a été observée et étudiée. La cristallisation des phases LaAlO3 et LaBO3 dans ces verres a été suivie par DRX (Haute Température). L’ajout de SiO2 à la composition La2O3-Al2O3 a été nécessaire pour élaborer un verre avec un four classique. Une étude de cristallisation poussée a été également menée sur de nouveaux verres d’aluminates d’alcalinoterreux. Cette étude a compris une caractérisation des vitrocéramiques formées ainsi que la résolution de la structure de deux nouveaux polymorphes de BaAl4O7 formés par cristallisation des verres en se servant de la diffraction électronique, neutronique et synchrotron. Une étude par RMN de l’évolution de l’environnement de l’oxygène durant le recuit a été réalisée et a permis de mettre en évidence la présence des entités d’oxygène tri-coordinées dans les verres d’aluminate de baryum. Ce travail nous a finalement permis d’élaborer plusieurs vitrocéramiques complètement cristallisées et transparentes, ce qui constitue un résultat exceptionnel. La luminescence de ces vitrocéramiques a été caractérisée et les raisons de leur transparence sont discutées à la lumière de leurs microstructures. / This thesis concerns the crystallization and the structural study of different alumino-silicate glasses. This study has led to several completely crystallized and transparent glass-ceramics, which is an original result for this type of material that usually loses transparency during crystallization. These innovative materials were the subject of a patent entitled “Transparent ceramics” (French deposit number: N° 1161025 and international extension number : PCT N° EP2012/074171) and different articles (cf. page 162). Numerous glasses in the systems rare earth oxides, alkaline earth oxides-Al2O3-SiO2 were prepared by an aerodynamic levitator coupled to a laser heating system and studied. The study of the YAG crystallization from the yttrium alumino-silicate glasses was achieved mainly by double resonance 27Al/29Si NMR spectroscopy and by (lab and synchrotron) X-ray diffraction. This study showed that the silicon ions that are initially present in the glassy matrix are incorporated during crystallization in the formed YAG crystals on the 4-fold coordination Al site. The structural consequences of this incorporation were studied. In particular, the reduction of the YAG cubic lattice and the bonds of the tetrahedral sites have been evidenced. Upon post synthesis annealing, the glass was observed to exhibit crystallization below the glass transition temperature. This unusual behaviour was examined using XRD and infrared spectroscopy to follow crystallinity and optical absorbance as a function of annealing treatment. This rarely reported phenomenon could be explained by the high tendency of our glass to crystallize compared to glasses elaborated by classical furnaces and by the ability of Si4+ to be accommodated into the YAG crystal structure as we have demonstrated. This study also revealed the influence of the refractive index difference between the glass and the crystals on the scattering of light. TEM and SEM images show that the YAG crystals sizes range between 500 nm and 1300 nm. Furthermore, the crystallization of a family of lanthanum aluminate and lanthanum borate glasses was studied. In both cases, the crystallization started from the surface. The formation of LaAlO3 LaBO3 phases in these glasses was followed by XRD (High Temperature). The addition of SiO2 to the Al2O3-La2O3 composition was found necessary for the vitrification with a conventional oven. Finally, a crystallization study was also conducted on new alkaline-earth aluminate glasses. This study included a characterization of the parent glasses with the formed glass-ceramics and the structure resolution of two new polymorphs of BaAl4O7 formed by crystallization, using electron neutron and synchrotron diffraction. An NMR study of the environment evolution of the oxygen during annealing was performed. This allowed to evidence the presence of tri-coordinated oxygen entities in the parent glasses. This work has finally allowed us to develop fully crystallized and transparent glass-ceramics, which is an exceptional result. The luminescence of these glass-ceramics was characterized and the reasons for their transparency were discussed in light of their microstructures.

Les céramiques transparentes élaborées par cristallisation complète du verre constituent une nouvelle famille de matériaux de qualité photonique en compétition avec la technologie des monocristaux pour les applications optiques. Cette approche verrière offre des avantages considérables par rapport aux monocristaux et aux céramiques polycristallines frittées : un coût réduit, la possibilité d’une production à grande échelle, une large gamme de compositions chimiques accessibles, une mise en forme plus souple et un taux de dopage élevé. Dans le cadre de ce travail, nous avons synthétisé des céramiques polycristallines transparentes de Sr3Al2O6 et Sr3Ga2O6 (structures cubiques) par cristallisation complète du verre de même composition. Les verres d'aluminate de strontium (75SrO-25Al2O3) et de gallate de strontium (75SrO-25Ga2O3) sont élaborés par lévitation aérodynamique couplée à un dispositif de chauffage laser. La transparence de la céramique de Sr3Al2O6 obtenue s’explique par son isotropie optique, ses joints de grains très fins et sa structure totalement dense (non poreuse). Nous avons également développé une nouvelle famille de céramiques transparentes Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) obtenues par cristallisation complète et congruente du verre. La transmission exceptionnelle de plus de 90% dans la gamme visible et proche infrarouge est expliquée grâce à des études microstructurales et structurales. Cette transparence qui atteint la limite théorique est associée à une biréfringence quasi nulle, des joints de grains très fins et une porosité nulle. Les études par RMN prouvent l'existence d'un désordre chimique qui est à l'origine de la valeur pratiquement nulle de la biréfringence calculée par DFT. Ces matériaux céramiques polycristallins évolutifs et hautement transparents sont des candidats prometteurs pour une large gamme d'applications optiques et photoniques dans les gammes IR et visible. Cette étude a donc conduit à de nouvelles céramiques transparentes, avec des valeurs de transmission jamais atteintes jusqu’à présent pour des oxydes. Elle propose également une nouvelle approche pour l'obtention de céramiques transparentes dans le cas de matériaux anisotropes : introduire un désordre chimique contrôlé au sein du matériau afin d’induire une isotropie optique. Ce concept ouvre la voie à de nouvelles compositions, étendant ainsi le domaine des céramiques transparentes et de leurs applications. / Transparent polycrystalline ceramics elaborated by full crystallization from glass are an emerging class of photonicquality materials competing with single crystal technology, especially for optical applications. This approach provides considerable advantages over single crystals and polycrystalline sintered ceramics represented by cost effectiveness, large scale production, wide range of accessible chemical compositions, easy shaping and high doping level hosting structure. In this work, we show the preparation of transparent cubic Sr3Al2O6 and Sr3Ga2O6 polycrystalline ceramics by full crystallization from the parent strontium aluminate (75SrO-25Al2O3) and strontium gallate (75SrO-25Ga2O3) glasses elaborated by aerodynamic levitation coupled to laser heating system. The transparency of the obtained Sr3Al2O6 ceramics is explained by their optical isotropy, thin grain boundaries and highly dense (non-porous) microstructure. We also show a series of novel Sr1+x/2Al2+xSi2-xO8 (0<x≤0.4) oxide compositions leading to highly transparent and readily scalable polycrystalline ceramics to be obtained by full congruent glass crystallization. The outstanding transparency exceeding 90% in the visible and near IR range is explained through different microstructural and structural (average and local) studies. This transparency, reaching the theoretical limit, is associated to the almost null birefringence, thin grain boundaries and non-porosity. NMR experiments prove the existence of chemical disorder which is at the origin of the relatively zero birefringence value calculated by DFT computations. These scalable and highly transparent polycrystalline ceramic materials are promising candidates for a wide range of optical and photonic applications in the IR and visible ranges. This study besides revealing new ceramic compositions with previously unreported transmission values for micro-scale polycrystalline materials, proposes a new approach for obtaining transparent ceramics in anisotropic materials. This approach consists in inducing a controlled chemical disorder within the material in order to induce optical isotropy. It is anticipated that this proposed concept will open the way to different composition candidates to be elaborated as transparent polycrystalline ceramics, thus extending the ceramic technology domain and its applications.

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.

No description available.

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.

Ordinary concrete is the most commonly used building material, but nowadays the requirements for low energy consumption, durability of structures together with their easy diagnostics as well as ecological production raises. This thesis deals with cement and aluminosilicate composites with content of conductive fillers, which allows to monitor the change in electrical properties, most commonly electrical resistance in dependence on mechanical stress. In the experimental part of the thesis, test beams were produced based on alkali-activated slag with content of carbon nanotubes, graphite powder, carbon black and carbon fibre. The beams were subjected to flexural loading in a three-point bending configuration and the shift in electrical resistance was monitored.

This dissertation deals with the study of electric and dielectric properties of composite structures on the base of alkali-activated aluminosilicates with admixtures of various carbon particles. These materials fabricated from alkali-activated blast furnace slag, quarz sand, natrium water glass as alkali activator, water, dispersant and small amount of carbon admixture (carbon black, graphite powder, carbon fibers or carbon nanotubes) to increase electric conductivity may be used for example to construction of snow-melting, deicing and self-monitoring systems. Their current-voltage characteristics and impedance spectra were used for determination of electric and dielectric properties of these structures. The equivalent circuits were used for evaluation of impedance spectra. The results were correlated with thermal properties of these structures.