Annealing characteristics and nature of traps in Al₂O₃ thermoluminescent phosphor

Abstract

Thermal annealing characteristics of the glow peaks from 200 to 650 degrees c in Al2O3 thermoluminescent (TL) phosphor have been studied. All the glow peaks show exponential decay and follow first-order kinetics. The trap depths and frequency factors for the glow peaks have been determined from their isothermal decay and from their initial rise. The trap depths, E, obtained for different glow peaks (peak temperature Tm) can be approximated by the relation E(eV)=Tm (K)/325 and the corresponding frequency factor, s, varies from 10(14) to 10(16) s-1. The measured values of E, s and Tm for the glow peaks are shown to be consistent with the equation for glow peak temperature. The annealing characteristics and actual high temperature irradiations show that the 250, 475 and 635 degree c peaks can be used for elevated temperature dosimetry up to 150, 300 and 440 degrees C respectively. 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 to be electrons by photostimulated thermoluminescence studies under the F centre excitation in this phosphor.