On the yellow color of gamma‐irradiated brazilianite from Minas Gerais (Brazil).

Resumo
The origin of gamma irradiation-induced strong yellow color in brazilianite from Brazil is investigated. The irradiation- induced optical absorption band responsible for the color shows an onset in the blue spectral region at about 2.5 eV and maximum centered in the UV at ~ 4.24 eV. From the ratio between the squared value of the line width (W2 ) and the peak energy (M), a value of about 0.09 eV is estimated, which is consistent with an absorption band caused by a Schirmer ́s-type O− bound small polaron. By electron paramagnetic resonance (EPR), we are able to confrm its microscopic structure. This O− hole center is in fact the Al3+–O−X2+–P5+ hole center already identifed by EPR earlier in the literature (where X2+ stands for a nearby divalent cation with negligible abundance of magnetic isotopes). The EPR spectrum of the Al3+–O−X2+–P5+ hole center, along with the O− bound small polaron absorption band responsible for the yellow color, appears simultane- ously at high concentrations after gamma irradiation, and vanishes together for thermal annealing above 300 °C, returning after re-irradiation in a reversible way. Their appearance is concomitant with the H0 centers and Ti3+ electron centers, and possible charge-compensating centers.
Descrição
Palavras-chave
Brazilianite, Electron paramagnetic resonance, Irradiation, Electron–hole center, O− hole center
Citação
PINHEIRO, M. V. B. et al. On the yellow color of gamma‐irradiated brazilianite from Minas Gerais (Brazil). Physics and Chemistry of Minerals, v. 48, 2021. Disponível em: <https://link.springer.com/article/10.1007/s00269-021-01159-1>. Acesso em: 29 abr. 2022.