Thermal Stimulation of Luminescence and Theory of the Glow Curves

Abstract

The chapter begins with the explanation of the thermal stimulation process and goes on to describe conventional models of thermoluminescence (TL). The characteristic properties of the glow curves of the Randall-Wilkins, the Garlick-Gibson, the general order (GO), and the mixed order (MO) kinetics models are summarized. While dealing with the GO kinetics model it is shown that the pre-exponential factor (PF) s′ and the kinetic order (KO) parameter b are not independent constants as assumed by the proponents of the model, but that the s′ value is dependent on the value of b and the total concentration N of the traps. The lacunae in GO kinetics model and the shortcomings of MO model are discussed. The chapter then takes up the physical models. These include the multitrap systems which are the simplified version of the generalized scheme consisting of a host of traps and equally large number of recombination centers (RC). These may plausibly be applicable to the real materials. It is shown by simulations how first order (FO) kinetics glow peaks are produced under a variety of parametric conditions. The results of these simulations are used to answer the question why the KO of the TL glow peaks of real materials is invariably seen to be of FO. It is suggested that thermally disconnected deep traps, which may be stable at high temperatures may contribute to the high concentration of RC (radiative or nonradiative) leading to the FO kinetics. It is logical that defects would exist in a crystalline material until it approaches its melting point. Examples are given of some materials in which deep traps have been detected. Another way by which FO kinetics is produced is the local recombination of the thermally excited charge carriers.