Dependence of quasi-equilibrium on heating rate and its use in the study of thermoluminescent materials

Using the simulated thermoluminescence (TL) glow peaks, it is shown that the level of quasi-equilibrium (QE) during the emission of a glow peak depends on the heating rate (β) used. Any system which may satisfy the QE condition when β is below a certain value during TL stimulation, may turn to the non-QE condition at higher values of β. The level of QE is examined in terms of the two functions called D(T) and q(T). A quantitative limit is suggested on the value of these functions in order to define a system as quasi-equilibrated. At about the turning point of the QE to non-QE condition the glow peaks begin to change their shape. This property is found for the first time and is used as the first ever experimental method to test whether or not the emission of a given glow peak is occurring under the QE condition. Further, at the QE to non-QE turning point the ratio TR/τm appears to be nearly constant with only a weak dependence on the values of τm where TR is the recording time of the glow peak and τm is the recombination lifetime of the free carriers during the peak emission. This near constant value of TR/τm together with the measured value of TR may be used to estimate the τm of the systems which show the non-QE condition above a certain heating rate. The value of τm being a function of the concentration and the cross section of the TL related traps, one is able to correlate the value of τm thus found with the approximate range of these parameters for the given sample. The results are discussed in the perspective of a well known TL phosphor and the plausible range of its concentration and cross section parameters.