PHOTOSTIMULATED AND THERMOSTIMULATED PROCESSES IN ALPHA-AL2O3

We reported on the recombination processes determined by the release o f electrons from defects connected with the dosimetric 430 K thermosti mulated luminescence (TSL) peak as well as with the 260 K TSL peak. Th ese TSL peaks appear in thermochemically reduced alpha-Al2O3 crystals containing hydrogen and emission of these TSL peaks corresponds to lum inescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced alpha-Al2O3 crystals doped with acceptor impurities results in the appearance of a broad a nisotropic complex absorption band in the spectral region 2.5-3.5 eV a nd in the appearance of a predominant TSL peak at 430 K. Above 430 K t he above-mentioned broad absorption band disappears. Optical bleaching of the 2.5-3.5 eV band is accompanied by the disappearance of the 430 K TSL peak and results in F-center emission. The X-ray or UV excitati on of reduced alpha-Al2O3 crystals with donor-type impurities results in the appearance of an anisotropic absorption band at 4.2 eV and the appearance of a dominant TSL peak at 260 K. Above 260 K the 4.2 eV abs orption disappears and photostimulated luminescence (PSL) of the F-cen ter recombination luminescence in the 4.2 eV region is no longer obser ved. Optical bleaching of the 4.2 eV absorption band is accompanied by the disappearance of the 260 K TSL peak. The successful use of reduce d alpha-Al2O3 in dosimetry needs the optimization of the concentration of all components (accepters, hydrogen, intrinsic defects) involved i n the thermo- and photostimulated processes.