Optical and ESR studies of hole centers in γ-irradiated Al2O3

Based on the studies of the thermal stability and the oxidizing annealing at 1350 °C, it is concluded that the one-hole center observed in a 300 K γ-irradiated Al2O3 crystal is predominantly the VOH- center. The OH− ions can be removed from the Al2O3 crystal by prolonged annealing in air at 1350 °C. The emission spectra show that the γ-ray induced thermoluminescence peaks at 390, 420, 440, 500, and 550 K peaks observed in oxidized and non-oxidized Al2O3 crystal are all related to the R-lines emission from Cr3+ in Al2O3. The 390, 420, and 500 K peaks result from thermal destruction of the hole centers by hole release. The 550 K peak is caused by the restoration of unperturbed, substitutional Cr3+ ions.