Mechanoluminescence produced during impulsive deformation of coloured alkali halide crystals

Mechanoluminescence (ML) in coloured alkali halide crystals is reported. During impulsive excitation of gamma-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 transfer of dislocation-trapped electrons to deep traps. In the frame work of the mechanism proposed, an equation is derived which is able to explain the ML in the deformation and post-deformation region of the crystal. Several other facts related to the ML produced during impulsive excitation of coloured alkali halide crystals, are also discussed.