Mechanoluminescence and Deformation Bleaching in Colored Alkali Halide Crystals

Abstract

The present paper reports the mechanoluminescence (ML) and
deformation bleaching of a colouration in coloured alkali halide
crystals. As the F-centre electrons captured by moving dislocations
are picked up by holes, deep traps and other compatible traps, so
deformation bleaching occurs. Simultaneously radiative recombination
of dislocation captured electrons with the holes gives rise to
the mechanoluminescence. Expressions have been derived for the
strain dependence of the density of colour centres is deformed
crystals and for the number of colour centres bleached. So far as
strain, temperature, density of colour centres, E_a and volume dependence
are concerned, there exists a correlation between the deformation
bleaching and mL in coloured alkali halide crystals. From
the strain dependence of the density of colour centres in deformed
crystals, the value of coefficient of deformation bleaching 0 is
found to be 1.929 and 1.990 for KCI and KBr crystals respectively.
The value of (D + χ) as determined from the strain dependence of
the ML intensity is found to be 2.59 and 3.69 for KCI and KBr
crystals respectively. This gives the value of coefficient of deformation
generated compatible traps  χ to be 0.68 and 1.69 for KCI
and KBr crystals respectively.