A model for explaining the concentration quenching of thermoluminescence

The effect of concentration quenching (CQ) of luminescence has been reported in the literature. The luminescence efficiency dependence on the concentration of a specific impurity was found to reach a maximum intensity for a certain concentration, and decline at higher concentrations. A formula has been developed for the dependence of the efficiency on the concentration, assuming that only activators not adjacent to other activators can emit luminescence. Curve fitting of the CQ experimental curves to the theoretical function resulted in very large values of the parameter z, the number of nearest neighbors, of up to 4000, which is not feasible. A similar effect was found in TL of some materials, and the same formula for explaining the effect was used. Medlin has described the TL properties of calcite and dolomite. For a 300 K peak in Pb++ doped calcite, he used the same function and found z = 700, and for a 410 K peak, he got z = 150; the maxima occurred at different concentrations. In the present work, we propose a possible, alternative model to explain the QC of thermoluminescence (TL). The model includes 3 trapping states and one recombination center (3T1C model). We assume that the 3 traps have a constant concentration, and the variable concentration is that of the recombination center M. An important assumption made is that the initial occupancy of M is not zero, and we assume that m(0) = 0.1M. The results yield the concentration dependence of the area under two simulated peaks reached by solving numerically the relevant set of six simultaneous rate equations. The maximum intensities of the two peaks occur at different concentrations, similarly to experimental results in Pb++ doped calcite and Mn++ doped dolomite. Approximate analytical derivations support these results. (C) 2011 Elsevier Ltd. All rights reserved.