Thermoluminescence associated with two-electron traps

Abstract

A model of thermoluminescence (TL) is presented based on a double-occupancy electron trap and a single-hole recombination center. The concept of double-electron traps has been established before with regard to different solid state phenomena and briefly mentioned as a possible occurrence in connection with TL. A new set of simultaneous differential equations governing the three stages of excitation, relaxation and readout of TL in this new framework is developed. This situation is dealt with by solving these sets of equations sequentially for reasonable sets of chosen trapping parameters. Also, an analytical treatment using plausible simplifying assumptions is given in parallel. The outcome of these procedures yields a two-peak TL curve and, in a sense, the two-electron trap behaves as two traps with different activation energies, frequency factors and retrapping probabilities. The results of the simulations and the approximate analytical approach show that the lower-temperature peak has features of first-order peak and is strongly superlinear with the dose of excitation. With the appropriate choice of parameters, the dose dependence of the first peak has been found to be cubic and slightly more than cubic with the excitation dose. This may explain experimental results of cubic and somewhat stronger superlinearity previously reported in the literature. The second peak has second-order features and it shifts dramatically to lower temperatures with increasing dose.