The Role of dislocations in the ML induced by slow deformation of coloured alkali halide crystals and II-VI semiconductors at fixed strain rates. The ML in coloured alkali halide crystals arises due to the mechanical interaction between the bending segments of dislocations and F-centres, and the ML in II-VI semiconductors arises due to the electrostatic interaction between the bending segments of dislocations and filled electron traps. When an ionic crystal is elastically deformed, the ML intensity increases linearly with time and it also increases linearly with increasing the strain rate of the crystals. But the total light emission for a given strain is the same. When the deformation is stopped, depending upon the prevailing condition the ML intensity decreases exponentially with time in which the decay time is equal to the relaxation time of the bending segments of dislocation, in the time constant for stopping