Centros de cor, centros paramagnéticos e centros de luminescência dependentes de defeitos pontuais em zirconita / Color center, paramagnetic center and luminescence center due the defect point in zircon

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

In the present work the investigation of some properties of Thermoluminescence (TL), Electronic Paramagnetic Resonance (EPR) and Optical Absorption (OA) of two samples of zircon (of brown color) from Minas Gerais, but the unknown exact origin, were carried out. The glow curves of thermoluminescence emission have shown the presence of 4 TL peaks at 140, 215, 270 and 350 ºC although strongly overlaped. By deconvolution more peaks were revealed. The intensity of the TL peaks at 140 and 215 ºC as function of the radiation dose presents linear and sublinear behavior. The TL emission spectrum has shown two bands at 480 and 580 nm, which are due to the Dy content in our sample. Appart from Dy many other elements are found in the sample, however, they do not participate in the TL emission. The EPR spectra of the irradiated powder sample showed a central signal whith g=2,000 that is due to the SiO45- center. This signal is isotropic and easily observed in the polycrystalline sample (in powder). In the monocrystalline sample non-isotropic signals can be observed due to EPR centers produced by irradiation. They are due to the loss or gain of one electron from the SiO44- group. The isocronal decay curves of the SiO45- signal and that of TL peaks are similar indicating a correlation between the EPR and TL centers suggesting us a possible TL mechanism: the Dy3+ looses one electron and converts into Dy4+ during irradiation. The electron liberated is then captured by SiO44- forming the SiO45- EPR center. When the sample is heated in order to read out TL the inverse process takesplace leaving the Dy3+ in excited states. In the transition to the ground state two light emissions are observed, one in 480nm and other in 580nm. In the OA spectrum measuremment two bands due to the Uranium (1100 and 1503nm), one to H2O(1900nm) and one due to the radical OH (1400nm) are observed. These bands are not afected by the irradiation used in this work.

ASSUNTO(S)

epr zircon epr zirconita

ACESSO AO ARTIGO

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