Thermally stimulated luminescence arising simultaneously from localized and delocalized recombination processes

The thermally stimulated luminescence (TSL) arising simultaneously from localized and delocalized recombination processes is studied theoretically for a wide range of recombination and retrapping probabilities. The model proposed by Braunlich and Scharmann (BS), which considers the excitation of trapped electrons to (i) the conduction band, (ii) the excited state of the trap and (iii) the electrons from the excited state of the trap which are further raised to the conduction band during the heating phase of the TSL phosphor, has been used in the present study. The rate equations of the model, which are 'stiff', are solved numerically for a wide range of parameters using the linear heating profile. It has been found that the glow peak temperature T-m can exhibit dose dependence in localized transitions under strong retrapping, i. e. r >> 1 (r is the retrapping parameter for localized transitions), whereas for the other values of r, the glow peak temperature Tm is independent of dose. The same is also true for the glow curve arising from localized recombination in the study of a semi-localized transitions model. The study shows that the order of kinetics of the TSL glow curve arising from localized recombination can be more than one as the glow peak temperature Tm can exhibit dose dependence. However, the BS model is of approximate character because the possibility that the recombination centre, which is likely to participate in localized process, may be emptied by a recombination transition from conduction band, i.e. via delocalized recombination process, has not been included and in such situations the BS model does not hold.