On the spectrum of the F-centres in the neighbourhood of charged dislocations

Abstract

Upon deformation of alkali halide crystals an electrical voltage can be observed between suitably placed electrodes due to the movement of charged dislocations. When the specimen is coloured, light induces electrical relaxation, the “dislocation photoconduction”. We analysed the spectrum of dislocation photoconduction as a spectrum of F-centres situated in the neigh-bourhood of charged dislocations. It is difficult to segregate the two competing effects on the F-spectrum, namely the electric and the strain field of the dislocation, so when we discussed our experimental data we had to assume that the change was caused by either the strain or the electric field. In this paper we discuss this problem theoretically by means of the method of moments. Comparing the expressions of the changes of the first and second moments for the strain field with the analogous ones for the Coulomb field of a charged dislocation jog we see that for every reasonable distance between the dislocation and the F-centre the effect of the strain field is the dominant one. The change of moments can be fitted to experimental data.