Correlation between deformation bleaching and mechanoluminescence in coloured alkali halide crystals

Abstract

The present paper reports the correlation between deformation bleaching of coloration and mechanoluminescence (ML) in coloured alkali halide crystals. When the -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 far as strain, temperature, density of colour centres, 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 is determined and it is found to be 1.93 and 2.00 for KCl and KBr crystals, respectively. The value of ( · ) is determined 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 to be 0.67 and 1.7 for KCl and KBr crystals, respectively.

Mechanoluminescence induced by elastic deformation of coloured alkali halide crystals using pressure steps

“…So far as the deformation at constant strain rate is concerned, the results reported for the dependence of ML intensity on strain at different strain rates indicate the increase of ML intensity for a given time t with the strain rate [34]. The ML intensity in the plastic region has been found to increase linearly with the strain rate [34,[40][41][42][43]. These results are in accordance with Eq.…”

“…Thus, U 0 =0.24 eV for KCl crystals. As the value of DU 0 is of the order of 0.10 eV for alkali halide crystals [26], (U 0 ÀDU 0 ) comes out to be of the order of 0.10 eV, which is comparable with the activation energy of the order of 0.10 obtained from the temperature dependence of ML of coloured alkali halide crystals, [25,[31][32][33][34]. As (U 0 ÀDU 0 ) is comparable to kT=0.026 eV at room temperature, it seems that the thermal activation energy will be sufficient to enable the interacting F-centre electrons to cross the potential barrier between the dislocation band and the interacting F-centre electrons lying in the expansion region of the edge of dislocations.…”

“…In other words, g i will be equal to g d if the activation energy E a , that is, the energy difference between the dislocation acceptor band and the ground state of the interacting F-centres, will be negligible as compared to kT, i.e., E a 5kT. In fact, for coloured alkali halide crystals, E a is of the order of 0.08 eV [25,[31][32][33][34], and kT at room temperature is of the order of 0.026 eV, giving E a 4kT. Thus, in the case of coloured alkali halide crystals, g d will be different from g i .…”

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals

“…Chandra et al [6] have studied the pressure and temperature dependence of the ML of g-irradiated alkali halide crystals. They have investigated the correlation between the deformation bleaching and ML [7] and the correlation between the acoustic emission and ML of the coloured alkali halide crystals [8]. Chandra et al [9][10][11] have shown that the mechanical interaction between the moving dislocations and F-centers is responsible for the ML of coloured alkali halide crystals.…”

Fracto‐mechanoluminescence induced by impulsive deformation of II–VI semiconductors

“…These are corrected here.A corrected Figure 11 (page 889) is given below.References 13,14,16,18,19,20,21,22,24,25,26 The publisher apologizes for these errors. …”