General-order kinetics of thermoluminescence and its physical meaning

Thermoluminescence glow peaks are calculated numerically for a one-trap-one-recombination-centre model using a generalized approach. Except in extreme cases the peaks are seen to change in position and shape with a change in dose. These glow peaks are fitted to the general-order kinetics model and the values of the kinetic parameters, namely the activation energy, pre-exponential factor and order of kinetics are determined by finding the best fit. In this way an attempt is made to correlate the empirical parameters with the physically meaningful ones in the framework of the adopted model. The fitted value of the activation energy matches reasonably its input value used in the generalized approach model calculations. The fitted values of the order of kinetics and the pre-exponential factor parameters change with the initial occupancy of the traps (dose) in all cases in which the order of kinetics (KO) is found to be in the range in which 1 < KO < 2. The KO decreases with increasing trap occupancy whereas the pre-exponential factor increases. The latter parameter undergoes a change also in its units. It is observed that, when the found value of the KO is such that 1 < KO < 2, the best fitted general-order kinetics peak deviates significantly from the computed peak. A better fit is found with two peaks, one of which is approximately of first order and the other approximately of second order. The KO parameter at saturation dose has been correlated with the ratio of the re-trapping and recombination cross sections. These theoretical results are discussed in the perspective of experimental observations in general. Plausible reasons for disagreements between theory and experiment are also discussed.