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Physical properties of materials and their constituents are interrelated. Though the basic structural unit involved also plays a role in deciding the properties, this can be manipulated to a certain extent, by carefully selecting the basic ingredients or by varying the composition. In order to tailor the properties of the materials according to the need, the relationship between the properties and the structure has to be established. Glasses, due to their inherent disorder, don’t have the privilege of using symmetry as enjoyed by their crystalline counterparts. Given their components and composition there is no immediate and easy way of predicting all the observed properties of glasses. This is not considering computer simulations and DFT calculations. Hence we go back to play with nature, i.e., do experiments. Technological applications like LASERs, optic fibers, photosensitive semiconducting thin films, solid state batteries for energy storage etc. have greatly increased the interest in the fundamental properties of disordered materials. Large coefficient of linear expansion of germanate glasses is made use in glass-to-metal seals for ultra high vacuum. More over, many germanate based glasses with specially tailored dispersion properties have been developed. GeO2 based glasses are in fibre optics in the IR region of 1.5 to 1.8 microns. Borate glasses are resistant to thermal and chemical attack. They lower the melting temperature of glasses thus facilitating large scale production.Both borates and germanates have been worked upon extensively. Alkali boro germanate systems are interesting inherently. Borates and Germanates both are glass formers by themselves. The continuous random network formed by this base glass is modified by the presence of alkali ions. It is interesting to see to what extent the alkali ions can maintain the local charge neutrality in their neighborhood by creating non bridging oxygen atoms and how the presence of two formers is stabilizing the glass matrix. Present Work This thesis work is an attempt to understand the structure of alkali borogermanate glasses 25R2O-25GeO2-(50-x)B2O3-xNd2O3:(R=Li, Na, K and Rb; x=0,0.5). A variety of experimental techniques are available to give a good insight of the structure of glass systems. In this thesis, we have carried out  Optical studies at room temperature to probe the environment of RE ion  AC conductivity at high temperature to probe the alkali ion dynamics  11B MASS NMR of doped systems at room temperature to probe the Boron sites  Raman and Mid-IR experiments at room temperature to probe the various structural groups to get a comprehensive understanding of the structure of these glasses. To facilitate the analysis of the data and discussion of the results from these experiments, the thesis is divided in to four chapters excluding the introduction as categorized above and is presented accordingly. The second chapter begins with the preparation of the glass samples and their characterization. We have used Differential Scanning Calorimetry (DSC), powder XRD and elemental analysis using ICP-OES for characterizing the sample. We have also measured the density and refractive index of the glasses under study. After this section, we describe the results from Optical Absorption and Photoluminescence studies. A brief description of Judd-Ofelt (JO) theory used for the analysis of the results is given. We have calculated the optical parameters and JO parameters and the energy levels of Nd ions in the glass matrix based on absorption studies using program written in Matlab. The procedure to calculate these parameters and their relevance in estimating the important quantities like radiative transfers, branching ratios are discussed. The effect of variation of the alkali ions on these properties is also discussed. In the third chapter, we have investigated AC conductivity in these glasses. These experiments are carried out both as a function of frequency (40 Hz - 15 MHz) and temperature (220 C – 500 C) using a home made portable furnace with a temperature controller. The cable compensation using open and short standards were done at the high temperature end. The data has been analyzed in Electric modulus (M*) formalism using Kohlrausch William Watts (KWW) function. The other basic models used in the literature like Debye, Cole-Cole, Cole Davidson and Havriliak Negami are briefly discussed. The frequency dependence of conductivity in these systems has been ascribed to the hopping motion of the alkali ions. Non-symmetric nature of the imaginary part of M* shows an evidence of non-exponential relaxation. Activation energies were estimated from the temperature variation of the KWW and DC. The fit parameters KWW and KWW shows interesting behavior. KWW in LGBNd and NGBNd show an initial increase with increasing temperature reaching a value of 1, while a contrasting behavior is observed in KGBNd and RGBNd. Barton-Nakajima-Namikawa (BNN) plot of the present study gives a value of 0.67 and 0.7 for the slope parameter p for doped and un-doped samples respectively. BNN plot is used to correlate the ac and dc conductivities in the sample. The deviation of the slope parameter from unity may be an indication of different charge carriers for ac and dc transport. Fourth Chapter describes the room temperature 11B MASS NMR studies in Nd doped glass system. The relevant theory of Zeeman, Dipolar, Quadrupolar and Chemical shift interactions are discussed briefly before the results. The principle used in obtaining high resolution NMR in solids by means Sample spinning is also described. NMR line shape for the central transition (1/2  -1/2) of I=3/2 nuclei (11B) was simulated in Mathematica and fitting was tried in Matlab. Using this background we have analyzed the line shape. In the next part, the results of 11B MASS NMR experiments of doped glasses carried out using Bruker DSX300 at 96.3MHz are presented. The fraction of contribution from four and three co-ordinated 11B to NMR line-shape were identified and calculated. The results show unambiguously the presence of two 3 coordinated 11B sites which were differentiated on the basis of the quadrupolar parameters. In the last chapter we discuss the results of Raman and Mid-IR investigations carried out in these glasses at room temperature. These two important techniques are well established in identifying the structural groups in glass systems. Raman bands observed in the range 200 cm-1 to 1600 cm-1 in these glasses are deconvoluted using gaussian peaks and they have been assigned to various modes of possible structural groups. Two broad MIR absorption bands were observed between 600cm-1 - 1600cm-1 in both doped and undoped glasses. Each band was resolved into gaussian peaks. The band shifts and the changes in the intensities are ascribed to the effects of variation of alkali, as the presence of GeO2 (up to 25mol%) is known not to affect the borate bands as it is a former by itself.

Neste trabalho é apresentado um estudo espectroscópico sobre vidros de germanato contendo nanopartículas (NPs) metálicas e semicondutoras dopados com íons de terras-raras (TRs) Eu3+, Nd3+ e Er3+ visando o desenvolvimento de novos materiais para aplicações em fotônica. Estes vidros apresentam larga janela de transmissão (400-4500 nm), alto índice de refração (~ 1,9), baixa energia de fônon (700 cm-1), alta resistência mecânica e durabilidade química. Com a finalidade de verificar a nucleação das NPs metálicas e semicondutoras, foram realizadas análises por Microscopia Eletrônica de Transmissão (MET) que indicaram a presença de NPs metálicas e semicondutoras. As técnicas de espectroscopia de fluorescência de raios X por energia dispersiva (EDS energy dispersive spectroscopy) e difração de elétrons comprovaram a natureza química das NPs. As medidas de absorção óptica evidenciaram a incorporação dos íons de TRs na forma trivalente, fenômeno responsável pela luminescência nos vidros, e permitiram as medidas das bandas de absorção relacionadas à ressonância dos plasmons superficiais e das bandas de absorção características de NPs de natureza semicondutora. Medidas de emissão foram realizadas através de diferentes procedimentos, que variaram de acordo com a natureza das TRs. Foram medidas intensas bandas de emissão da luz vermelha do Eu3+ relacionadas com as transições 7F J (J=0 a 6) -> 5D0, bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm relacionadas com as transições 2H 11/2 -> 4I 15/2 , 4S 3/2 -> 4I 15/2 e 4F 9/2 -> 4I 15/2 respectivamente, e bandas de emissão de luz na região do infravermelho do Nd3+ em 900, 1076 e 1350 nm relacionadas com as transições 4F 3/2 -> 4I 9/2 , 4F 3/2 -> 4I 11/2 e 4F 3/2 -> 4I 13/2 . Foi observado aumento significativo da luminescência da luz vermelha do Eu3+ nas amostras contendo NPs de prata, ouro, e prata juntamente com ouro. Nas amostras contendo NPs de silício foi observado aumento significativo da emissão associada à conversão ascendente de freqüências do érbio. Os aumentos ocorridos na luminescência das amostras contendo NPs metálicas são provavelmente causados pelo aumento do campo local nas proximidades dos íons de TRs e pela transferência de energia entre as NPs e os íons deTRs. Os aumentos ocorridos na luminescência das amostras contendo NPs semicondutoras são provavelmente causados pela transferência eficiente de energia entre as NPs e os íons de TRs originada da recombinação de éxcitons dentro das NPs semicondutoras. Portanto, a presença das NPs desempenha um papel importante para o aumento da luminescência, permitindo o desenvolvimento de novos materiais com aplicações em nanofotônica. / This work presents a spectroscopic study about Eu3+, Nd3+ and Er3+ rare-earth doped germanate glasses containing metallic and semiconductor nanoparticles (NPs) aiming the development of new materials for photonic applications. These glasses have a large transmission window (400-4500 nm), high refractive index (~ 1.9), low phonon energy (700 cm-1), high mechanic resistance and chemical durability. Transmission Electronic Microscopy analysis was performed to verify the metallic and semiconductor NPs nucleation, and indicated the presence of metallic and semiconductor NPs. X ray fluorescence by energy dispersive spectroscopic (EDS) and electron diffraction analysis showed the chemical nature of the NPs. Optic absorption measurement proved the trivalent incorporation of the rare-earth ions, the responsible phenomenon for the luminescence of the glasses that allowed the measurement of the absorption bands related to the superficial plasmon resonance. Emission measurements were performed with different procedures, related to nature of the rare-earth. High emission bands of Eu3+ were measured related to the 7F J (J=0 to 6) -> 5D 0 transitions; emission bands associated to the frequency upconversion of Er3+ in 530, 550 and 670nm related to the 2H 11/2 -> 4I 15/2, 4S 3/2 -> 4I 15/2 e 4F 9/2 -> 4I 15/2 transitions were observed, and as well as emission bands of Nd3+ in 900, 1076 and 1350 nm related with the 4F 3/2 -> 4I 9/2, 4F 3/2 -> 4I 11/2 e 4F 3/2 -> 4I 13/2 transitions. A significant enhancement of the red light luminescence of Eu3+ was observed in the samples containing silver, gold, and silver together with gold NPs. For the samples containing silicon NPs it was observed a considerable enhancement of the frequency upconversion emission of the erbium. The luminescence enhancement of the samples with metallic NPs is due to the enhancement of the local field nearby the rare-earth ions and/or to the energy transfer between the NPs and the rare-earth ions. The luminescence enhancement of the samples with semiconductor NPs are due to the efficient energy transfer between the NPs and the rare-earth ions originated from the excitons recombination inside the semiconductor NPs. Therefore, the presence of the NPs plays an important role on the luminescence enhancement, allowing de development of new materials for nanophotonic applications.

Neste trabalho é apresentado um estudo espectroscópico sobre vidros de germanato contendo nanopartículas (NPs) metálicas e semicondutoras dopados com íons de terras-raras (TRs) Eu3+, Nd3+ e Er3+ visando o desenvolvimento de novos materiais para aplicações em fotônica. Estes vidros apresentam larga janela de transmissão (400-4500 nm), alto índice de refração (~ 1,9), baixa energia de fônon (700 cm-1), alta resistência mecânica e durabilidade química. Com a finalidade de verificar a nucleação das NPs metálicas e semicondutoras, foram realizadas análises por Microscopia Eletrônica de Transmissão (MET) que indicaram a presença de NPs metálicas e semicondutoras. As técnicas de espectroscopia de fluorescência de raios X por energia dispersiva (EDS energy dispersive spectroscopy) e difração de elétrons comprovaram a natureza química das NPs. As medidas de absorção óptica evidenciaram a incorporação dos íons de TRs na forma trivalente, fenômeno responsável pela luminescência nos vidros, e permitiram as medidas das bandas de absorção relacionadas à ressonância dos plasmons superficiais e das bandas de absorção características de NPs de natureza semicondutora. Medidas de emissão foram realizadas através de diferentes procedimentos, que variaram de acordo com a natureza das TRs. Foram medidas intensas bandas de emissão da luz vermelha do Eu3+ relacionadas com as transições 7F J (J=0 a 6) -> 5D0, bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm relacionadas com as transições 2H 11/2 -> 4I 15/2 , 4S 3/2 -> 4I 15/2 e 4F 9/2 -> 4I 15/2 respectivamente, e bandas de emissão de luz na região do infravermelho do Nd3+ em 900, 1076 e 1350 nm relacionadas com as transições 4F 3/2 -> 4I 9/2 , 4F 3/2 -> 4I 11/2 e 4F 3/2 -> 4I 13/2 . Foi observado aumento significativo da luminescência da luz vermelha do Eu3+ nas amostras contendo NPs de prata, ouro, e prata juntamente com ouro. Nas amostras contendo NPs de silício foi observado aumento significativo da emissão associada à conversão ascendente de freqüências do érbio. Os aumentos ocorridos na luminescência das amostras contendo NPs metálicas são provavelmente causados pelo aumento do campo local nas proximidades dos íons de TRs e pela transferência de energia entre as NPs e os íons deTRs. Os aumentos ocorridos na luminescência das amostras contendo NPs semicondutoras são provavelmente causados pela transferência eficiente de energia entre as NPs e os íons de TRs originada da recombinação de éxcitons dentro das NPs semicondutoras. Portanto, a presença das NPs desempenha um papel importante para o aumento da luminescência, permitindo o desenvolvimento de novos materiais com aplicações em nanofotônica. / This work presents a spectroscopic study about Eu3+, Nd3+ and Er3+ rare-earth doped germanate glasses containing metallic and semiconductor nanoparticles (NPs) aiming the development of new materials for photonic applications. These glasses have a large transmission window (400-4500 nm), high refractive index (~ 1.9), low phonon energy (700 cm-1), high mechanic resistance and chemical durability. Transmission Electronic Microscopy analysis was performed to verify the metallic and semiconductor NPs nucleation, and indicated the presence of metallic and semiconductor NPs. X ray fluorescence by energy dispersive spectroscopic (EDS) and electron diffraction analysis showed the chemical nature of the NPs. Optic absorption measurement proved the trivalent incorporation of the rare-earth ions, the responsible phenomenon for the luminescence of the glasses that allowed the measurement of the absorption bands related to the superficial plasmon resonance. Emission measurements were performed with different procedures, related to nature of the rare-earth. High emission bands of Eu3+ were measured related to the 7F J (J=0 to 6) -> 5D 0 transitions; emission bands associated to the frequency upconversion of Er3+ in 530, 550 and 670nm related to the 2H 11/2 -> 4I 15/2, 4S 3/2 -> 4I 15/2 e 4F 9/2 -> 4I 15/2 transitions were observed, and as well as emission bands of Nd3+ in 900, 1076 and 1350 nm related with the 4F 3/2 -> 4I 9/2, 4F 3/2 -> 4I 11/2 e 4F 3/2 -> 4I 13/2 transitions. A significant enhancement of the red light luminescence of Eu3+ was observed in the samples containing silver, gold, and silver together with gold NPs. For the samples containing silicon NPs it was observed a considerable enhancement of the frequency upconversion emission of the erbium. The luminescence enhancement of the samples with metallic NPs is due to the enhancement of the local field nearby the rare-earth ions and/or to the energy transfer between the NPs and the rare-earth ions. The luminescence enhancement of the samples with semiconductor NPs are due to the efficient energy transfer between the NPs and the rare-earth ions originated from the excitons recombination inside the semiconductor NPs. Therefore, the presence of the NPs plays an important role on the luminescence enhancement, allowing de development of new materials for nanophotonic applications.

Materiais vítreos com propriedades similares às do cristal germanato de bismuto de composição Bi4Ge3O12, material cintilador que possui estrutura do tipo eulitita, são de interesse devido as suas propriedades luminescentes, que os tornam promissores para aplicação como dispositivos ópticos. Vidros do sistema GeO2-Bi2O3 (BGO) também tem sido tema de inúmeras pesquisas por combinarem um típico formador vítreo (GeO2) a um formador condicional composto intermediário (Bi2O3), o que os proporciona características estruturais únicas, resultantes da mudança de coordenação dos átomos de germânio (fenômeno de anomalia do germânio) e também dos átomos de bismuto. Neste trabalho, estudou-se a influência da adição de CeO2, comumente conhecido como agente oxidante, nas propriedades físico-químicas de vidros de germanato de bismuto do sistema [100-x].[(1-y)GeO2-yBi2O3]:xCeO2 (para x = 0,2 ou 1 e y = 0,2 ou 0,3 % em mol), preparados pelo método de fusão e moldagem. O escurecimento inomogêneo das amostras, associado à termoredução do íon Bi3+, foi evitado com a adição de céria, que se mostrou um modificador da estrutura local dos vidros, mesmo para uma dopagem de 0,2 % em mol. Foi observada, pela primeira vez, a cristalização da fase de estrutura eulitita cintiladora induzida pela presença de Ag na superfície do vidro de composição 99,8[0,8GeO2- 0,2Bi2O3 ]:0,2CeO2 % em mol, referido pela sigla 80BGO:0,2Ce, abaixo da temperatura de transição vítrea (Tg). A difusão de Ag no vidro é condição necessária para que o fenômeno da cristalização aconteça, uma vez que esse elemento pode ser considerado um efetivo agente nucleante para a fase cintiladora. A cristalização induzida é favorecida pela tensão gerada na interface cristal/vidro, devido a uma diferença de volume molar entre essas duas fases, o que permite que o fenômeno da cristalização seja observado em temperturas inferiores à Tg. / Glassy materials with similar properties to those of the bismuth-germanate crystal in the composition of Bi4Ge3O12, a scintillator material with the eulytite structure, are of interest due to their luminescent properties that makes them promising materials to application as optical devices. Glasses from the system GeO2-Bi2O3 (BGO) has also being subjects of numerous studies, by combining a typical glass former oxide (GeO2) with the conditional one intermediate compound (Bi2O3). The presence of these two oxide compounds in the glass composition provides them a unique structural characteristic resulting from the coordination changes of germanium atoms (germanium anomaly phenomenon) and also of the bismuth atoms. In the present work, it was studied the influence of CeO2 addition, commonly known as an oxidant agent, in the physical-chemical properties of the bismuth-germanate glasses up to the system [100-x].[(1-y)GeO2-yBi2O3 ]:xCeO2 (for x = 0.2 or 1 and y = 0.2 or 0.3 mol %), prepared by the melting/molding method. The inhomogeneous darkening of the samples, associated to the thermal reduction of the Bi3+ ions, was avoided by the ceria addition that acts as a local modifier of the glass structure even for concentrations of 0.2 mol %. It was observed, by the first time, the crystallization of the eulytite scintillator phase, induced by the presence of Ag in the surface of the glass in the 99[0.8GeO2- 0.2Bi2O3 ]:0.2CeO2 mol % composition, referred to as 80BGO:0.2Ce, below the glass transition temperature (Tg). The Ag diffusion into the glass is a necessary condition to the crystallization phenomenon since this element can be considered as an effective nucleating agent to the scintillator phase. The crystallization is favored by the tension generated in the crystal/glass interface, due to a difference in molar volume of these two phases, allowing that the crystallization phenomenon be observed at temperatures below Tg.

Materiais vítreos com propriedades similares às do cristal germanato de bismuto de composição Bi4Ge3O12, material cintilador que possui estrutura do tipo eulitita, são de interesse devido as suas propriedades luminescentes, que os tornam promissores para aplicação como dispositivos ópticos. Vidros do sistema GeO2-Bi2O3 (BGO) também tem sido tema de inúmeras pesquisas por combinarem um típico formador vítreo (GeO2) a um formador condicional composto intermediário (Bi2O3), o que os proporciona características estruturais únicas, resultantes da mudança de coordenação dos átomos de germânio (fenômeno de anomalia do germânio) e também dos átomos de bismuto. Neste trabalho, estudou-se a influência da adição de CeO2, comumente conhecido como agente oxidante, nas propriedades físico-químicas de vidros de germanato de bismuto do sistema [100-x].[(1-y)GeO2-yBi2O3]:xCeO2 (para x = 0,2 ou 1 e y = 0,2 ou 0,3 % em mol), preparados pelo método de fusão e moldagem. O escurecimento inomogêneo das amostras, associado à termoredução do íon Bi3+, foi evitado com a adição de céria, que se mostrou um modificador da estrutura local dos vidros, mesmo para uma dopagem de 0,2 % em mol. Foi observada, pela primeira vez, a cristalização da fase de estrutura eulitita cintiladora induzida pela presença de Ag na superfície do vidro de composição 99,8[0,8GeO2- 0,2Bi2O3 ]:0,2CeO2 % em mol, referido pela sigla 80BGO:0,2Ce, abaixo da temperatura de transição vítrea (Tg). A difusão de Ag no vidro é condição necessária para que o fenômeno da cristalização aconteça, uma vez que esse elemento pode ser considerado um efetivo agente nucleante para a fase cintiladora. A cristalização induzida é favorecida pela tensão gerada na interface cristal/vidro, devido a uma diferença de volume molar entre essas duas fases, o que permite que o fenômeno da cristalização seja observado em temperturas inferiores à Tg. / Glassy materials with similar properties to those of the bismuth-germanate crystal in the composition of Bi4Ge3O12, a scintillator material with the eulytite structure, are of interest due to their luminescent properties that makes them promising materials to application as optical devices. Glasses from the system GeO2-Bi2O3 (BGO) has also being subjects of numerous studies, by combining a typical glass former oxide (GeO2) with the conditional one intermediate compound (Bi2O3). The presence of these two oxide compounds in the glass composition provides them a unique structural characteristic resulting from the coordination changes of germanium atoms (germanium anomaly phenomenon) and also of the bismuth atoms. In the present work, it was studied the influence of CeO2 addition, commonly known as an oxidant agent, in the physical-chemical properties of the bismuth-germanate glasses up to the system [100-x].[(1-y)GeO2-yBi2O3 ]:xCeO2 (for x = 0.2 or 1 and y = 0.2 or 0.3 mol %), prepared by the melting/molding method. The inhomogeneous darkening of the samples, associated to the thermal reduction of the Bi3+ ions, was avoided by the ceria addition that acts as a local modifier of the glass structure even for concentrations of 0.2 mol %. It was observed, by the first time, the crystallization of the eulytite scintillator phase, induced by the presence of Ag in the surface of the glass in the 99[0.8GeO2- 0.2Bi2O3 ]:0.2CeO2 mol % composition, referred to as 80BGO:0.2Ce, below the glass transition temperature (Tg). The Ag diffusion into the glass is a necessary condition to the crystallization phenomenon since this element can be considered as an effective nucleating agent to the scintillator phase. The crystallization is favored by the tension generated in the crystal/glass interface, due to a difference in molar volume of these two phases, allowing that the crystallization phenomenon be observed at temperatures below Tg.