Photoplastic effect in alkali halides

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Abstract
The photoplastic effect first reported by Nadeau has been extensively investigated in colored crystals of NaCl, KCl, KBr, and KI. Detailed data on its dependence on strain level, F-center concentration, strain rate, light intensity, and light wavelength have been obtained. The excitation spectrum of the photoplastic effect follows closely the shape of the F absorption band at room temperature as well as liquid-nitrogen temperature. On the other hand, the magnitude Δτ of the effect fits the law Δτ = C1(1 + C2v/I)−1, v being the average dislocation speed, I the light intensity, and C1 and C2 constants. A theoretical model which takes into account the light-induced formation of an electron cloud around charged moving dislocations is proposed. Quantitative expressions for the dependence of the effect on light intensity and wavelength have been obtained which are in accordance with experimental data. Other implications of this work on light-induced dislocation pinning and dislocation-induced photoconductivity are briefly analyzed.

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