Thermoluminescence associated with two-hole recombination centers

A model of thermoluminescence (TL) is presented based on a double-occupancy hole-recombination center and a single-electron trap. The concepts of double-electron traps and double-hole centers have been established before with regard to different solid state phenomena and also mentioned as a possible occurrence in connection with TL. In a recent paper, we dealt with the TL associated with a two-electron trap and a one-hole center. Here, we consider the case of one-electron traps and two-hole centers. 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, to some extent, the two-hole center behaves as two centers with different recombination probabilities. The results of the simulations and the approximate analytical approach show that the lower-temperature peak has usually features of first-order peak and its intensity is superlinear with the dose of excitation. With the appropriate choice of parameters, the dose dependence of the first peak has been found to be initially quadratic with the excitation dose. This may explain experimental results of quadratic dose dependence previously reported in the literature. The second peak has second-order features and both peaks shift to lower temperatures with increasing dose. This effect is explained by a change in the effective frequency factor with the excitation dose.