Estudo das propriedades ópticas e estruturais de espinélios do tipo 'ZNAL IND. 2 O IND. 4' contendo 'EU POT. 3+' ou 'TB POT. 3+'
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Data
2008-09-26
Autores
Silva, Alison Abreu da [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Neste trabalho foram estudadas propriedades ópticas e estruturais dos espinélios ZnAl2O4 e Zn5In2O8 puros e dopados com íons de terras raras através dos métodos sol-gel e Pechini visando aplicações em dispositivos emissores de campo, field emission displays, (FED). Ambos os métodos se mostraram eficientes na síntese das fases desejadas, destacando-se a metodologia sol-gel que proporcionou a obtenção de ZnAl2O4 nanoparticulado a partir de 300 ºC. As técnicas FTIR e RMN de estado sólido indicam que a estrutura espinélio deve apresentar dois diferentes sítios de simetria AlO6, sendo um de alta simetria, e que a relação entre eles varia com a temperatura de síntese. Além disso, as amostras obtidas em baixas temperaturas apresentam inversão de estrutura, ou seja, íons Al 3+ presentes em sítios tetraédricos. As amostras de ZnAl2O4 obtidas por ambos os métodos apresentam luminescência dependente das condições de tratamanto; tanto devido à formação de defeitos estruturais nas amostras obtidas por Pechini, como relacionadas a efeitos de confinamento quântico nas amostras obtidas via sol-gel. A fase Zn5In2O8 apenas foi obtida por Pechini. O material, de cor amarela, com caráter semicondutor (bandgap ~2,5 eV) não apresenta luminescência nas condições da medida. Nas amostras de ZnAl2O4 dopadas até 10 % em mol não foram observadas fases de óxidos de terras raras e o perfil do difratograma indica diminuição do tamanho de partícula com a concentração de dopantes. Nas amostras de Zn5In2O8 contendo terras-raras observa-se segregação de fase, formação de EuInO3 ou TbInO3, a partir de 5% em mol de dopante. A dopagem de ZnAl2O4 com Eu3+ revelou a presença de pelo menos dois sítios sem centro de inversão e que a relação entre eles deve variar com a temperatura de tratamento ou a porcentagem de dopante. Um dos sítios (A) apresenta bandas largas indicando...
Structural and spectroscopic investigations of pure and rare-earth doped ZnAl2O4 and Zn5In2O8 spinels obtained by the sol-gel and Pechini methods were carried out in order to be applied in the Field Emission Displays (FEDs) technology. Both methods were very efficient in the main phase preparation, specially the sol-gel route which promotes the synthesis of crystalline ZnAl2O4 at 300 ºC. The aluminium microsymmetry changes with heat treatment temperature. The spinel structure might present two distinct AlO6 sites with different symmetries in ZnAl2O4 and the ratio between them may change with temperature as evidenced by 27 Al solid-state magic-angle-spinning nuclear magnetic resonance spectra. This behavior is in good agreement with the FTIR measurements, from which it was possible to distinguish different AlO6 sites, being one of them endowed with a higher symmetry. The ZnAl2O4 samples presented luminescence dependence on the heat treatment temperature due to the structural defects formation in the samples prepared by Pechini or due to quantum size effects regarding the samples prepared by the sol-gel method. The Zn5In2O8 phase was obtained only by Pechini and presents a semiconductor character (~2,5 eV of bandgap). No luminescence could be detected from this phase in the measurement conditions. In the ZnAl2O4 doped samples, no impurities of any residual rare-earth phases could be observed up to 10 at.% of doping. Broad diffraction peaks indicate a small crystallite size with increase dopant concentration. For the Zn5In2O8 doped samples, adjacent phases (EuInO3 or TbInO3) could be observed when the doping level reaches 5% at. The luminescence spectroscopy of Eu3+ reveals that it may occupy at least two non-centrosymmetrical sites and that their ratio might be dependent on the heat treatment or doping level. One of them (site A) presents strongly inhomogeneous broadening... (Complete abstract click electronic access below)
Structural and spectroscopic investigations of pure and rare-earth doped ZnAl2O4 and Zn5In2O8 spinels obtained by the sol-gel and Pechini methods were carried out in order to be applied in the Field Emission Displays (FEDs) technology. Both methods were very efficient in the main phase preparation, specially the sol-gel route which promotes the synthesis of crystalline ZnAl2O4 at 300 ºC. The aluminium microsymmetry changes with heat treatment temperature. The spinel structure might present two distinct AlO6 sites with different symmetries in ZnAl2O4 and the ratio between them may change with temperature as evidenced by 27 Al solid-state magic-angle-spinning nuclear magnetic resonance spectra. This behavior is in good agreement with the FTIR measurements, from which it was possible to distinguish different AlO6 sites, being one of them endowed with a higher symmetry. The ZnAl2O4 samples presented luminescence dependence on the heat treatment temperature due to the structural defects formation in the samples prepared by Pechini or due to quantum size effects regarding the samples prepared by the sol-gel method. The Zn5In2O8 phase was obtained only by Pechini and presents a semiconductor character (~2,5 eV of bandgap). No luminescence could be detected from this phase in the measurement conditions. In the ZnAl2O4 doped samples, no impurities of any residual rare-earth phases could be observed up to 10 at.% of doping. Broad diffraction peaks indicate a small crystallite size with increase dopant concentration. For the Zn5In2O8 doped samples, adjacent phases (EuInO3 or TbInO3) could be observed when the doping level reaches 5% at. The luminescence spectroscopy of Eu3+ reveals that it may occupy at least two non-centrosymmetrical sites and that their ratio might be dependent on the heat treatment or doping level. One of them (site A) presents strongly inhomogeneous broadening... (Complete abstract click electronic access below)
Descrição
Palavras-chave
Química inorgânica, Luminescencia, Estrutura espinélio, Dopagem, Inorganic chemistry
Como citar
SILVA, Alison Abreu da. Estudo das propriedades ópticas e estruturais de espinélios do tipo 'ZNAL IND. 2 O IND. 4' contendo 'EU POT. 3+' ou 'TB POT. 3+'. 2008. 82 f. Dissertação (mestrado) - Universidade Estadual Paulista, Instituto de Química, 2008.