Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals

The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured alkali halide crystals. When the F-centre electrons captured by moving dislocations are picked up by holes, deep traps and other compatible traps, then deformation bleaching occurs. At the same time, radiative recombination of dislocation captured electrons with the holes gives rise to the mechanoluminescence. Expressions are derived for the strain dependence of the density of colour centres in deformed crystals and also for the number of colour centres bleached. So fa r as strain, temperature, density of colour centres, E-a and volume depende nce are concerned, there exists a correlation between the deformation bleac hing and ML in coloured alkali halide crystals. From the strain dependence of the density of colour centres in deformed crystals, the value of coeffic ient of deformation bleaching D is determined and it is found to be 1.93 an d 2.00 for KCl and KBr crystals, respectively. The value of (D + chi) is de termined from the strain dependence of the ML intensity and it is found to be 2.6 and 3.7 for KCl and KBr crystals, respectively. This gives the value of coefficient of deformation generated compatible traps chi to be 0.67 an d 1.7 for KCl and KBr crystals, respectively.