GENERAL ORDER KINETICS OF THERMOLUMINESCENCE - A COMPARISON WITH PHYSICAL MODELS

The general order kinetics expression of thermoluminescence (TL) conta ins two empirical parameters, namely the kinetics order (KO) and the p re-exponential factor (PF). In this paper thermoluminescence glow curv es are calculated by assuming well defined physically meaningful model s and the KO and the PF values applicable to these glow curves are cal culated. The approaches used to find these values are either analytica l or based on the shape of the glow curves or their isothermal decay b ehaviour depending on the type of the model used. The results show tha t the KO and the PF parameters are in general not constant for a given glow peak. They vary with the change in occupancy of the traps except under the two limiting conditions, namely KO equal to 1 or 2. This me ans that, when the KO of a given glow peak is not equal to either 1 or 2, its numerical value as well as that of the PF would depend on the sample dose. It also means that these parameters change continuously w hen the glow curve is being recorded. At very low trap occupancies the se parameters approach limiting values. For the simple one-trap model this limiting value of KO is 2 whereas that for a multi-trap model is 1. The corresponding changes in the quantitative values of the PF are by large orders of magnitude and the variation is in the direction opp osite to that of the KO. Furthermore, the dimensions for the PF also c hange. These results bring the general order kinetics approach into co nflict with the physical models used to describe the TL glow curves. I mplications of these theoretical results for experimental observations are discussed.