Theory of Mechanoluminescence Kinetics in Coloured Alkali Halide Crystals

During impulse excitation of mechanoluminescence (ML) in X- or γ-irradiated alkali halide crystals, two peaks are observed in the ML intensity versus time curves. The first peak lies in the deformation region and the second peak in the post-deformation region. The ML in the deformation region is due to the recombination of dislocation-trapped electrons with the holes in defect centres. The ML in the post-deformation region is due to the transient thermostimulated luminescence from shallow traps which get populated due to the Auger process occurring during the transfer of dislocation-trapped electrons to deep traps. In the framework of the mechanism proposed, an equation is derived which is able to explain the ML in the deformation and post-deformation regions of the crystals. The equation is also able to explain the occurrence of two peaks in the ML kinetics. Several other facts related to the ML kinetics of coloured alkali halide crystals are also discussed.