Correlation between OSL and the distribution of TL traps in Al2O3:C.

Al2O3:C single crystals are known to exhibit some variation of their thermoluminescence (TL) glow curve shape from sample to sample. This variation is attributed to the fact that the TL peak in Al2O3:C is produced by the set of several traps. It is important to understand what part of the trap distribution correlates with the optically stimulated luminescence (OSL) process in this material. Crystals with a difference in the full-width, half-maximum (FWHM) of the TL peak as big as 30% and crystals having double-peak glow curves were used in this study. It was found that bleaching with a wavelength longer than 525 nm depletes mostly the low temperature part of the TL glow curve, leaving the high temperature peak unaffected. It was shown that when the pre-irradiation annealing temperature was increased from 500 to 1000 degrees C, the high temperature part of the abnormal double peak disappears. The phototransferred luminescence (PTTL) processes and conversion of F and F+ centres were also studied for samples having different glow curves shape. The practical aspect of this research is important for OSL dosimetry, because such crystals with wide or double TL peak can make it difficult to bleach OSL dosemeters for very low dose measurements.