Hamburg, Universiẗat, Diss., 2001.

No description available.

A Thulium Germanate thin disk laser prototype is developed and its potential applications are discussed. Unfortunately, the thin disk gain material for the CW prototype was unable to lase due to thermal limitations within the disk. However, a CW output power model and a physical pump chamber module have been developed, along with the supporting Zemax models and alignment procedures so other gain materials and future improvements can be tested.

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.

Há um crescente interesse científico e tecnológico voltado para compostos cristalinos de óxido de bismuto com óxidos de germânio, silício ou titânio, por exibirem propriedades eletro e magnetoópticas, fotocondutivas e piezoelétricas. Sistemas vítreos com propriedades similares a estes compostos são de alto interesse, devido ao baixo custo e facilidade no procedimento de preparação em relação aos monocristais. Este trabalho teve como finalidade analisar o efeito de adição de óxidos de boro e gálio, ao sistema binário composto por óxido de bismuto com óxidos de germânio. A amostra vítrea de composição 45BiO1.5:40BO1.5:15GeO2 (BBG-8), apresentou alta reprodutibilidade e estabilidade térmica (ΔT=132, Hr=0.34 e S=26.74), sendo assim, selecionada para o estudo da cristalização. As fases cristalizadas nesta amostra, durante tratamento térmico, foram determinadas por análises de difração de raios-X e medidas composicionais. Foram cristalizadas as fases Bi6B10O24 e Bi4Ge3O12, sendo a última, a fase de interesse para nosso estudo. Métodos térmicos foram utilizados no estudo da cristalização da fase Bi4Ge3O12, possibilitando a verificação da energia de ativação (≈ 54Kcal/mol) pelos métodos de Ozawa e Chen, e a direcionalidade do crescimento dos cristais (nmédio=1.12). A fim de obtermos mais informações a respeito de cristalização utilizamos óptica eletrônica. / The sillenite crystals, Bi12MO20 (M = Ge, Si, Ti), are interesting for applications such as optical memories, holography or optical phase conjugating devices. The eulytite crystals, Bi4M3O12, have been studied for their electro-optical, electromechanical and luminescence properties. These crystals am used as scintillators or, when doped with rare-earth elements, as laser materials. The study of glass systems, having properties similar to those crystals, is of high interest because of the lower cost and easier preparation procedures with respect to single crystals. The purpose of this work is the study of interaction of B2O3 and Ga2O3 with binary system Bi2O3-GeO2. The glassy sample BBG-8 (45BiO1.5:40BO1.5:15GeO2), was chosen far crystallition study, due to its high reproducibility and thermal stability. The presence of crystalline phases (Bi6B10O24 and Bi4Ge3O12), obtained after heat treatment, was investigated by powder X-ray diffraction and compositional analysis. The crystalline eulytite phase (Bi4Ge3O12) is an interest of our study. Thermal methods were used on the study of Bi4Ge3O12crystallization process of the sample BBG-8, and the value obtained, by means of Ozawa and Chen methods, was approximately 54Kcal/mol, and the directionality of crystal growth (n average) was equal to 1.12. To obtain further information on the crystallization mechanism we also performed microphotographic analysis.

<p>This thesis is focussing on the crystallographic challenges and what knowledge we can gain from studying the different open-framework germanates. Five new open-framework germanates have been synthesized and the structures have been determined by single crystal X-ray diffraction. A thorough description is made of the different problems raised with the different compounds, whether it is choice of crystal system in SU-61, twinning and possible ordering in SU-46, superstructure and variation in elemental content in SU-57, template disorder in JLG-5 or framework disorder in SU-44.</p><p>Open-framework germanates are often built from one type of cluster, such as the Ge₇ [Ge₇X₁₉], Ge₈ [Ge₈X₂₀], Ge₉ [Ge₉X_n, n =25-26] and Ge₁₀ [Ge₁₀X₂₈], (X =O, OH, F) clusters. The structures built by clusters containing different kinds of polyhedra are discussed, with a focus on the 4-coordinated Ge₇ clusters, the larger cluster aggregate found in SU-8 and SU-44 and the structures built by the Ge₁₀ clusters.</p>

This thesis is focussing on the crystallographic challenges and what knowledge we can gain from studying the different open-framework germanates. Five new open-framework germanates have been synthesized and the structures have been determined by single crystal X-ray diffraction. A thorough description is made of the different problems raised with the different compounds, whether it is choice of crystal system in SU-61, twinning and possible ordering in SU-46, superstructure and variation in elemental content in SU-57, template disorder in JLG-5 or framework disorder in SU-44. Open-framework germanates are often built from one type of cluster, such as the Ge7 [Ge7X19], Ge8 [Ge8X20], Ge9 [Ge9Xn, n =25-26] and Ge10 [Ge10X28], (X =O, OH, F) clusters. The structures built by clusters containing different kinds of polyhedra are discussed, with a focus on the 4-coordinated Ge7 clusters, the larger cluster aggregate found in SU-8 and SU-44 and the structures built by the Ge10 clusters.

Há um crescente interesse científico e tecnológico voltado para compostos cristalinos de óxido de bismuto com óxidos de germânio, silício ou titânio, por exibirem propriedades eletro e magnetoópticas, fotocondutivas e piezoelétricas. Sistemas vítreos com propriedades similares a estes compostos são de alto interesse, devido ao baixo custo e facilidade no procedimento de preparação em relação aos monocristais. Este trabalho teve como finalidade analisar o efeito de adição de óxidos de boro e gálio, ao sistema binário composto por óxido de bismuto com óxidos de germânio. A amostra vítrea de composição 45BiO1.5:40BO1.5:15GeO2 (BBG-8), apresentou alta reprodutibilidade e estabilidade térmica (&#916;T=132, Hr=0.34 e S=26.74), sendo assim, selecionada para o estudo da cristalização. As fases cristalizadas nesta amostra, durante tratamento térmico, foram determinadas por análises de difração de raios-X e medidas composicionais. Foram cristalizadas as fases Bi6B10O24 e Bi4Ge3O12, sendo a última, a fase de interesse para nosso estudo. Métodos térmicos foram utilizados no estudo da cristalização da fase Bi4Ge3O12, possibilitando a verificação da energia de ativação (&#8776; 54Kcal/mol) pelos métodos de Ozawa e Chen, e a direcionalidade do crescimento dos cristais (nmédio=1.12). A fim de obtermos mais informações a respeito de cristalização utilizamos óptica eletrônica. / The sillenite crystals, Bi12MO20 (M = Ge, Si, Ti), are interesting for applications such as optical memories, holography or optical phase conjugating devices. The eulytite crystals, Bi4M3O12, have been studied for their electro-optical, electromechanical and luminescence properties. These crystals am used as scintillators or, when doped with rare-earth elements, as laser materials. The study of glass systems, having properties similar to those crystals, is of high interest because of the lower cost and easier preparation procedures with respect to single crystals. The purpose of this work is the study of interaction of B2O3 and Ga2O3 with binary system Bi2O3-GeO2. The glassy sample BBG-8 (45BiO1.5:40BO1.5:15GeO2), was chosen far crystallition study, due to its high reproducibility and thermal stability. The presence of crystalline phases (Bi6B10O24 and Bi4Ge3O12), obtained after heat treatment, was investigated by powder X-ray diffraction and compositional analysis. The crystalline eulytite phase (Bi4Ge3O12) is an interest of our study. Thermal methods were used on the study of Bi4Ge3O12crystallization process of the sample BBG-8, and the value obtained, by means of Ozawa and Chen methods, was approximately 54Kcal/mol, and the directionality of crystal growth (n average) was equal to 1.12. To obtain further information on the crystallization mechanism we also performed microphotographic analysis.

The thesis reports the results of the research carried out towards the development of an electrooptic sensor for DC and extra low frequency electric field measurement. Available cubic electrooptic crystals were compared from the sensor sensitivity point of view. A new figure of merit was used taking into account the attenuation of the electric field in the dielectric crystal and its shape. The effect of optical activity in 23 cubic crystals was analyzed using the concept of Poincare sphere. The cubic crystals were further characterised for the charge relaxation time constant to estimate their performance in DC field measurements. Crystals of Bismuth Germanate and Lithium Niobate were identified as suitable materials for the DC field sensor. The selected crystals were found suitable at extra-low-frequencies. DC field measurements, without the rotation of the crystal, were possible only with Lithium Niobate. However, its performance was influenced to a great extent by the effect of stimulated conductivity. The quarter-wave plate and the crystal of Lithium Niobate were identified as the main sources of temperature instability. A new method of temperature compensation of the quarter-wave plate is proposed. Due to the temperature instability of Lithium Niobate, mainly attributed to the pyroelectric effect and natural birefringence, it is difficult to use the sensor in practical applications. The performance of the sensor is significantly affected by the presence of an external space charge. The proposed method of its elimination using an artificial extension of the sensing element did not reduce the space charge effect adequately. The response of the sensor in a space charge environment was found to be linear and independent of the space charge density. This enabled measurements of static fields in a unipolar environment. The direct field measurements in bipolar environment suffered from a drift which is intolerable in practical measurements. The minimum detectable electric field of this sensor in the frequency range from 1 to 200Hz was 1V/m, with a signal to noise ratio equal to 0dB and a resolution of 1V/m. The static field measurements were limited to measurements of pulses with a duration of 200s, due to a long term drift of photodetectors. The minimum detectable level of DC electric field was 2.4kV/m.

De nouveaux matériaux à base de BaAl2O4 et BaZnGeO4 ont été caractérisés. BaAl2O4 et les phases dérivées sont ferriélectriques: la polarisation spontanée possède deux composantes de sens opposes et d'intensités différentes. Un modèle a été propose pour justifier l'apparition d' une phase non stoechiométrique dérivée de BaAl2O4.BaZnGeO4 est pyroélectrique a 300K; cinq transitions de phase ont été mises en évidence. Les céramiques de BaZnGeO4 se polarisent spontanément au cours du traitement thermique en raison du caractère piezoélectrique du matériau.