The thermal and photo induced transformations of luminescence centers in anion defective crystals of α Al 2 O 3 have been investigated. It has been found that the exposure of crystals to ultraviolet light at temperatures in the range 50-900°C leads to substantial changes in their thermoluminescence and radioluminescence spectra. According to the optical absorption and photoluminescence data, the detected F type centers have been identified and the temperature ranges of the F F + F 2 transformations and their possible mechanisms have been determined. The special attention has been drawn to the detailed simi larity in the formation of complex F 2 type centers in the initially perfect α Al 2 O 3 crystals irradiated with fast neutrons and in the studied anion defective crystals.

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