935 resultados para pairing correlation


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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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In this work we studied the structural and optical properties of lithium tantalate (LiTaO3) powders doped with Eu3+ ions. We have examined the different sites occupied by the rare earth ion through the correlation of the DRX data analyzed with the Rietveld method and some spectroscopic parameters derived from the Eu3+ luminescence. Adirect relation was established between the lattice parameters and the occupation fraction of Eu3+ in each LiTaO3 site. The occupation fraction was set as the relative population of Eu3+ ions for each site obtained by means of the intensity, baricenter, and the spontaneous emission coefficients of the D-5(0)-> F-7(0) transitions. We concluded that the unit cell parameter a presents the same behavior of the Eu3+ occupation fraction in Ta5+ sites as a function of the Eu3+ content in LiTaO3. The same was observed for the variation in Eu3+ occupation fraction in the Li+ site and the unit cell parameter c with the Eu3+ content. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3204967]

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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The ZnO luminescent properties are strongly influenced by the preparation method and they are principally related to electronic and crystalline structures. This work reports about the correlation among luminescence properties of ZnO, obtained from zinc hydroxycarbonate, and crystalline lattice defects, microstrain, as function of thermal treatment. The crystallite size increase and the qualitative microstrain, obtained by Williamson-Hall plots, decrease as function of temperature. The evolution of electronic defects is analyzed by luminescence spectroscopy based on energy of the electronic transitions. From excitation spectrum, it is verified two bands around 377 nm and 405 nm attributed to the transitions between valence-conduction bands and valence band to interstitial zinc level, respectively. The emission spectra of sample treated at 600 degreesC shows large band at 670 nm. However, the green emission around 530 nm is observed for samples treated at 900 degreesC. The intensities of excitation and emission bands are associated with the increase of the electronic defects that depend on the strain lattice decrease. The lowest strain lattice results on the best green luminescent properties of zinc oxide. (C) 2001 Elsevier B.V. Ltd. All rights reserved.