Temperature dependence of pulse-induced mechanoluminescence excitation in coloured alkali halide crystals

In practice, the relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased or decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescence (ML) intensity increases with temperature. The ML intensity of first peak,I ml, second peak,I m2 and the total ML intensity,I T, initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio,I m2/I ml, is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.