Thermal dependence of time-resolved blue light stimulated luminescence in α-Al2O3:C

This paper presents time-resolved optically stimulated luminescence (TR-OSL) experiments in the important dosimetric material Al2O3:C. During these experiments short pulses (0.5 s) of light from blue LEDs (470 nm) are followed by relaxation periods (2.5 s) of the charge carriers at different stimulation temperatures. During the pulse excitation period the integrated TR-OSL signal increases with the stimulation temperature between 50 and 150 °C, while between 160 and 240 °C the signal intensity decreases. This behavior is interpreted to arise from competing effects of thermal assistance (activation energy, Eth=0.067±0.002 eV) and thermal quenching (activation energy W=(1.032+0.005) eV). Changes in the shape of the TR-OSL curves were analyzed at different stimulation temperatures using analytical expressions available in the literature. The TR-OSL signals contain a slower temperature-dependent phosphorescence signal, the “delayed-OSL” described previously for this material. The temperature dependent luminescence lifetimes obtained from analysis of the optical stimulation period are identical to those obtained from the corresponding relaxation period. However, the values of these luminescence lifetimes are systematically higher than previously reported values from time-resolved photoluminescence (TR-PL) studies carried out in this important dosimetric material. These results are discussed within the context of a recently published kinetic model.