Coordenação local do Eu(III) em híbridos orgânicos/inorgânicos emissores de luz branca
AUTOR(ES)
Carlos, Luís D., Ferreira, Rute A. Sá, Zéa Bermudez, Verónica de, Bueno, Luciano A., Molina, Celso, Messaddeq, Younes, Ribeiro, Sidney J. L.
FONTE
Química Nova
DATA DE PUBLICAÇÃO
2001-08
RESUMO
Eu3+ luminescence and EXAFS (Extended X-ray Absorption Fine Structure) results are presented for organic-inorganic hybrid gel hosts composed of a siliceous network to which small chains of oxyethylene units are covalently grafted by means of urea bridges. Coordination numbers for Eu3+ ions range from 12.8 to 9.7 with increasing Eu3+ concentration while the Eu3+-first neighbours mean distance is found to be constant at 2.48-2.49 Å in the same concentration range. Emission spectra display a broad band in the green/blue spectral region superposed to narrow lines appearing in the yellow/red region in such a way that for the eyes emission appears white. The broad band is assigned to intrinsic NH groups emission and also to electron-hole recombination in the nanosised siliceous domains. The narrow lines are assigned to intra-4f6, 5D0->7F0-4 Eu3+ transitions and from the energy position of the 7F0-4 levels a mean distance could be calculated for the Eu3+-first neighbours. The calculated results are in good agreement with the experimental ones obtained from EXAFS analysis.
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