Made available in DSpace on 2014-10-09T12:31:38Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:05Z (GMT). No. of bitstreams: 1 02286.pdf: 3044750 bytes, checksum: 753f2e5a876a0a848f90cf7bcb06b0e5 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

No description available.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Robert G. Hunsperger, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

No description available.

No description available.

No description available.

Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-28Bitstream added on 2014-06-13T18:28:59Z : No. of bitstreams: 1 gordo_vo_me_ilha.pdf: 1058796 bytes, checksum: 2c8438704796726349dfe606c2595b4b (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho foi estudado o sistema vítreo (100-x)% (80% TeO2-20% WO3)-(x)% Yb2O3, onde x = 0; 0,1; 0,2; 0,3; 0,4 e 0,5%. As técnicas de difração de raios-X, espectroscopia no infravermelho, espectroscopia Raman e espectroscopia no UV-Vis foram usadas para caracterizar os efeitos da dopagem sobre as propriedades estruturais e ópticas dos vidros estudados. Usando os dados de espectroscopia na região espectral ultravioleta-visível foi possível observar que não houve mudança das freqüências de corte para cada composição e ainda calcular a energia de “gap” e a energia de cauda de Urbach. Usando os dados de fotoluminescência observam-se picos que indicam o desdobramento dos níveis de energia dos estados 2F7/2 e 2F5/2 dos íons de Yb3+. Para os comprimentos de onda de excitação de 514,5 a 488,0 nm, crescem as taxas de absorção do sistema vítreo TW, transferência de carga para o estado 2F5/2 do Yb3+ e da transição radiativa 2F5/2 2F7/2, aumentando, desta forma, a intensidade da fotoluminescência. Já para os comprimentos de onda de excitação 457,9 e 476,5 nm as taxas de absorção do sistema vítreo TW, a transferência de carga para o estado 2F5/2 do Yb3+ e a transição radiativa 2F5/2 2F7/2 são as mesmas e, consequentemente, a intensidade da fotoluminescência é constante. / This work presents the study on the glassy system (100-x)% (80% 20% TeO2-WO3) - (x)% Yb2O3 where x = 0, 0.1, 0.2, 0.3, 0.4 and 0 5%. The techniques of X-ray diffraction, infrared spectroscopy, Raman spectroscopy and UV-Vis were used to characterize the effects of Yb doping on the structural and optical properties of the glasses. Using data from spectroscopy ultraviolet-visible spectral region was observed that there was no change of cutting frequencies for each compound and were calculate the energy gap and Urbach tail energy. Using the data of photoluminescence peak is observed indicating the splitting of energy levels of states 2F7/2 and 2F5/2 of Yb3+ ions. The rate of electron transition probability is influenced by temperature. To the excitation wavelength of 514.5 to 488.0 nm, growing rates of absorption of the glass system TW, charge transfer to the state 2F5/2 of Yb3+ and the radiative transition 2F5/2 2F7/2, increasing thus the photoluminescence intensity. As for the excitation wavelength of 476.5 and 457.9 nm absorption rates of the TW glass system, the charge transfer state to the 2F5/2 of Yb3+ and the radiative transition 2F5/2 2F7/2 are the same and, hence the photoluminescence intensity is constant.

Orientador: Sidney José Lima Ribeiro / Banca: Marcelo Nalin / Banca: Regina Célia Galvão Frem / Banca: José Maurício Almeida Caiut / Banca: Lauro June Queiroz Maia / Resumo: Nanoestruturas unidimensionais de telúrio (Te1D) na forma de whiskers, fios e hélices foram preparados com facilidade por uma síntese em etapa única na presença de solução aquosa de Pluronic® F68 à baixas temperaturas (< 100 °C) e pressão ambiente. A forma das nanoestruturas puderam ser controladas de acordo com a cinética da reação. Estruturas empacotadas de nanowhiskers e nanofios de Te foram obtidas via auto-organização em interface líquido-líquido e pela técnica de drop-cast em substrato de Si/SiO2. Estruturas híbridas 1D foram obtidas utilizando nanoestruturas Te1D como molde de sacrifício para anexar nanopartículas metálicas ou mesmo produzir nanoestruturas 1D metálicas. Por exemplo, nanoestruturas híbridas 1D foram preparadas decorando nanofios de Te com nanopartículas de Ag em solução aquosa de poli(vinilpirrolidona). Nanoestruturas 1D de Au com forma de nódulos foram preparados por deslocamento galvânico de íons Au3+ em uma mistura de nanohélices de Te, ácido ascórbico e solução aquosa de poli(vinilpirrolidona). Além disso, nanohélices de Te foram funcionalizadas com uma camada resina resorcinol-formaldeído em condições brandas de síntese. A resina de resorcinol-formaldeído é uma via intermédia para explorar a deposição de compostos opticamente ativos tais como nanopartículas de hidroxicarbonato de Tb3+ ou nanopartículas de Au. Para aplicações práticas é essencial que estas nanoestruturas possam ser suportadas em filmes rígidos ou flexíveis de alta qualidade óptica. ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: One-dimensional Te nanostructures (Te1D) in the shape of whiskers, wires and helices were prepared by a facile one-pot synthesis in the presence of aqueous Pluronic® F68 solution at low temperatures (< 100 ºC) and ambient pressure. The shape of Te1D nanostructures could be manuvered according with the reaction kinectics. We evaluate some techniques to assemble Te1D nanostructures on the pursuit for complex nanoarchitectures. Bundles of Te nanowhiskers and nanowires were achieved by self-assembly in liquid-liquid interface or by drop-cast technique in Si/SiO2 substrates. 1D hybrid structures have been conceived by using Te1D nanostructures as sacrificial template to attach metallic nanoparticles or even produce metallic 1D nanostructures. For example, 1D hybrid nanostructures were easily prepared by decorating Te nanowires with Ag nanoparticles in aqueous solution of poly(vinylpyrrolidone). Au 1D nanostructures with nodular-like shape were prepared by galvanic displacement of Au3+ ions in a mixture of Te nanohelices, ascorbic acid and an aqueous solution of poly(vinylpyrrolidone). Furthermore, Te1D nanohelices were functionalized with a layer of resorcinol-formaldehyde resin at mild synthesis conditions. The RF resin allowed us to fashion an intermediate pathway to explore the deposition of optically active compounds like Tb3+ hydroxylcarbonate or Au nanoparticles. Seeking practical applications, these nanostructures should be hosted over rigid or flexible films possessing exc... (Complete abstract click electronic access below) / Doutor

This dissertation contributes to the crystal chemistry of Te. The primary goals of the thesis are synthesis and crystal structure analysis of new Te-bearing ternary phases. The first part of the thesis shows significance of experimental mineralogy in research of Te containing systems. It briefly describes a novel approach to the study of new mineral species - the possibility of using synthetic analogues for their detailed mineralogical characterization. The results of the experimental mineralogical study in the Ni-Sb-Te ternary system at 400řC are reported in the second part. According to the performed experiments, two solid solutions λ1- Ni(Sb1-xTex)1+y (0<x<1, where 109.09.0 ≤≤⇒≥≈∀ yx ) and λ2 - NiSb1-xTe2x (0.28<x<0.66) dominate the system at 400řC. A characteristic feature of most phases present in the Ni-Sb-Te system at 400řC is apparent tendency to the Sb - Te substitution. The third part deals with the characterisation of the new mineral pašavaite Pd3Pb2Te2, which was found at the Noril'sk-Talnakh Ni-Cu camp, Russia. The synthetic Pd3Pb2Te2 phase was used for thorough mineralogical characterization of this new mineral species. Pašavaite displays orthorhombic symmetry, space group Pmmn. The structural identity between natural grains and synthetic Pd3Pb2Te was supported by the EBSD study. The...