Annealing characteristics and nature of traps in Al₂O₃ thermoluminescent phosphor

Thermal annealing characteristics of the glow peaks from 200 to 650 degrees C were studied. All the glow peaks show exponential decay and followed first-order kinetics. The trap depths and frequency factors for the glow peaks were determined from their isothermal decay and from their initial rise. The trap depths, E, obtained for different glow peaks (peak temperature T_m) can be approximated by the relation E(eV)=T_m (K)/325 and the corresponding frequency factor, s, varies from 10¹⁴ to 10¹⁶ s^-1. It is suggested that surface defects related to Si impurity in Al₂O₃, propagated into the lattice on high temperature treatment close to the melting point, are responsible for the TL traps. The trapped charges responsible for TL are shown, by photostimulated thermoluminescence studies, to be electrons.