Non-monotonic dose dependence of thermoluminescence (TL) revisited

Abstract

The effect of non-monotonic dose dependence of TL intensity on the irradiation dose has been reported in some materials in the past. As opposed to the regular case in which the intensity of the emitted TL light increases monotonically with the applied dose until it reaches saturation, in some reported cases, the light intensity reached a maximum and then declined at higher doses. The effect has been explained by using an energy level model including two electron traps and two hole centers competing with each other, thus yielding the effect. In the present work we show that with the use of certain sets of trap and center parameters, the effect can be seen with a reduced model of one trapping state and two recombination centers. Also, in recent years some experimental results showed more complex non-monotonic dose dependence, namely that following a maximum in the dose-intensity curve, and a certain range of decline, the TL intensity starts to increase again with the dose. We offer a new physical model that may explain this wiggly dose dependence. The energy-level diagram we propose is the same as before, with one electron trap and two kinds of recombination centers, one of which is radiative. In addition, we assume that the high energy radiation can produce more defects in the material which form more radiative recombination centers, this in addition to the filling of new and existing traps and centers by the irradiation. We consider the simultaneous differential equations governing the processes during irradiation, relaxation and heating with the variable dose-dependent concentration of the radiative recombination centers. We solve the equations numerically and by an analytical way with plausible approximations. The wiggly dose dependence results with certain sets of the relevant parameters.