The temperature dependence of the luminescence from Eu 2+ activators in BaFBr:Eu 2+ photostimulated between 10 and 300 K in the optical absorptions of F centres produced by room temperature X-irradiation, revealed two thermally-activated processes. The photostimulated luminescence (PSL) increases sharply in intensity when excited between 60 and 100 K. After the low-temperature PSL is exhausted by continuous F centre excitation, it can be almost entirely regained by warming the crystal to 300 K. This thermal cycle can be repeated several times. It is shown by EPR that no Eu 3+ is formed upon X-irradiation at 300 K. These results are explained with a model for the PSL mechanism which involves a loose aggregate of Eu 2+ , F, and hole centres.
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Hangleiter et al. (1990) studied this question.