Made available in DSpace on 2014-10-09T12:54:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:15Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP / FAPESP:05/57580-2

Made available in DSpace on 2014-10-09T12:54:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:15Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / No presente trabalho o comportamento de fusão de soluções sólidas do tipo LiGd1-xLuxF4 foram estudadas utilizando a técnica de fusão zonal, tendo em vista o desenvolvimento de novas matrizes para lasers do estado sólido. Os cristais de composição LiGd0,5Lu0,5F4 foram sistematicamente investigados. A caracterização física e química dos lingotes obtidos mostrou que este composto apresenta fusão incongruente. Posteriormente foram estudadas algumas composições do LiGd1-xLuxF4 (x = 0,60; 0,65 e 0,75), para estabelecer a composição a partir da qual começa a formação de compostos congruentes no pseudosistema LiGdF4-LiLuF4. A caracterização dos lingotes, utilizando-se as técnicas de microscopia eletrônica de varredura, espectrometria de energia dispersiva e difração de raios X, permitiu determinar que o LiGd1-xLuxF4 torna-se congruente a partir de valores de x em torno de 75 mol%. Nesta etapa do trabalho, as sínteses e os processos de fusão zonal foram realizados sob atmosfera reativa de HF, para garantir a obtenção de compostos de alta pureza. Dois monocristais de composições nominais de LiGd0,25Lu0,75F4 e LiGd0,232Lu0,75Nd0,018F4 foram crescidos com sucesso utilizando-se o método de Czochralski, sob atmosfera de Ar + CF4. A partir dos dados de concentração dos constituintes, obtidos por ICP-OES, para o cristal do dopado com neodímio, verificou-se que o íon Lu e o Gd apresentam variação de composição ao longo do cristal, sendo que a incorporação do íon Nd na rede compete com a do Gd. O valor médio calculado para o coeficiente de segregação do Nd nesta matriz foi de 0,22(1), para o Lu foi de 1,10(1) e para o Gd foi de 0,61(1). A espectroscopia de absorção mostrou que houve um alargamento das bandas em relação às bandas do LiLuF4:Nd. As secções de choque de absorção e os tempos de vida do nível 4F3/2 foram obtidos para três amostras com composições diferentes de Nd. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP / FAPESP:05/57580-2

Single crystals of cerium doped lutetium yttrium orthosilicate scintillator (Ce:(Lu(1-X)YX)2SiO5; Ce:LYSO) were grown through Czochralski method to investigate the affection of different growth conditions on the crystal growth. The relationship between thermal field and crystal growth was investigated. Different growth parameters and insulating system were adopted and compared to decrease the temperature gradient. It is found that the new insulating bricks can decrease effectively the temperature gradient and solve the crack problem of grown crystal. The relationship between materials ratio and the impurities in crystals. It is found that the optimized material ratio is Lu2O3:Y2O3:CeO2:SiO2=1.8563:0.1397:0.008:1.99. Under this ratio, we can get the crystals with best macroscopic optical quality. The scintillation properties of grown Ce:LYSO single crystal were measured. Through comparing the data with those in published literatures, it is found that the grown Ce:LYSO crystals present outstanding optical transmission, reaching the theoretical value about 84% in the visible light region. The transmission, UV-excitation and emission spectra are almost identical with the reported ones. The luminescence efficiency (LE) of random chosen 43 Ce:LYSO¡@samples were measured on the £^-ray multi-channel energy spectrum. It is found that the Ce:LYSO samples present stable luminescence efficiency with minimum channel number 3636.37, maximum channel number 4293.78, maximum deviation of 9.91% and standard deviation of 152.24 (3.77%). Annealing treatments were carried out in the air atmosphere on the small pieces of Ce:LYSO single crystals to eliminate the oxygen vacancies in the sample. It is found that the optimized annealing condition to improve the luminescence efficiency of Ce:LYSO is 1400 ¢J, 80 h under air atmosphere.

High quality YbxY1-xAG (0≤x≤1) single crystals were grown by using the Czochralski method. The structural properties of YbxY1-xAG (0≤x≤1) single crystals were also investigated using the EXAFS method. Additionally, for the first time, EXAFS results were compared with XRD results. Moreover, without essential lattice structure transformation, YbxY1-xAG crystals can be found due to the varying of doping concentration in XRD measurements. However, EXAFS measurements indicated that the local fine structural variation around the Yb3+ ion depends on the Yb3+ concentration. This work also studies the two-photon luminescence spectra of a Yb3+ doped YAG crystals. To study the spectral performance of Yb:YAG crystal, intense green light (centered at about 544nm) was generated by the crystal upon excitation using a 973nm InGaAs LD pump source. The luminescence spectra were obtained for various Yb concentrations and the emission intensity were plotted versus Yb3+ concentration. The green emission light attributed to Yb3+ two-photon transition.

¡@¡@This paper mainly focuses on the discussion about how to grow a large-sized highly-doped laser crystal- Neodymium yttrium aluminum garnet( {NdxY1-x}3Al5O3; Nd:YAG). The higher concentration of Nd:YAG crystal can allow the better efficiency of the laser. Since the ion size doped with Nd3+ ( R= 1.12A ) is larger than the ion size of Y3+ (R= 1.01A ), in the lattice of YAG, it¡¦s not easy to mix the smaller Y3+ site with the larger diameter of the Nd3 + ion. Therefore, the higher concentration of the laser crystal we want to grow, the more difficult work it is. ¡@¡@This experiment works under the use of the Czochralski technique to grow the laser crystal: Nd:YAG, and explore the impacts of different crystal pulling growth conditions on the growth of Nd:YAG crystal. Through adjusting the parameters of crystal growth, the crystal growth environments and the thermal fields, I discuss how to solve the problems of the scattering, cracking and spiral growing during the crystal growth process in order to improve the quality of the crystals. ¡@¡@Finally, comparing the results of a variety of spectral analysis (X-ray diffraction, UV / Vis Spectroscopy, Raman Spectroscopy, PL Spectroscopy) on the slice samples of Nd:YAG crystal which grew by our laboratory with the literature results, we can find that the X-ray diffraction pattern, the absorption spectroscopy, the Raman spectroscopy and the Photoluminescence spectroscopy of the Nd:YAG crystals grew in this experiment are consistent with the literature.

Made available in DSpace on 2014-10-09T12:55:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:58Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:46:16Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:47Z (GMT). No. of bitstreams: 1 07973.pdf: 3168450 bytes, checksum: 8bf87743d796e20893798cadfbfad208 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:55:21Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:58Z (GMT). No. of bitstreams: 0 / A utilização de lasers de estado sólido bombeados por diodos laser tem atraído interesse crescente devido a sua alta eficiência, seu tamanho compacto e com a possibilidade da operação com altas potências-pico. O objetivo deste trabalho foi estudar configurações de cavidades ressonantes laser, que possibilitem a obtenção de pulsos chaveados Q e futura dobra de freqüência, para aplicações em LIDAR (Light Detection and Ranging), utilizando como meio ativo cristais de Nd:YLF crescidos pelo método de Czochralski no Centro de Lasers e Aplicações IPEN USP, com bombeio lateral por diodo laser, com uma, duas, quatro e nove reflexões internas totais do feixe laser na superfície do cristal. Das seis cavidades construídas, três cavidades foram desenvolvidas para operarem com baixo ganho, grande armazenamento de energia e com grande aproveitamento de inversão de população, bombeadas com diodo laser em 806 nm e outras três cavidades foram desenvolvidas para operarem com alta absorção de bombeio e alto ganho, bombeadas com diodo laser emitindo em 797 nm. Das seis cavidades desenvolvidas, as que apresentaram melhor eficiência de conversão óptica, foram as cavidades operando com alto ganho e alta absorção (cavidade quatro a seis), com 29,5% e 20,7% de eficiência de conversão óptica, propiciando a obtenção de pulsos chaveados de 20 ns com potência-pico de 160kW. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1977 / Vita. / Includes bibliographical references. / by Edward Paul Martin, Jr. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

Made available in DSpace on 2014-10-09T12:35:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:05Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP