Optical Probing of the Environment ofFCenters in Deformed Alkali Halides

Abstract

The formation of $F$ centers upon ${\mathrm{Co}}^{60}$ irradiation of KCl deformed at room temperature and at 77°K and the environment of $F$ centers formed upon ${\mathrm{Co}}^{60}$ irradiation of deformed KBr were studied by means of optical-absorption measurements with a Cary-14 spectrophotometer. Anomalies of the beta absorption band (exciton band localized at the $F$ centers) and shift of the $F$-center peak toward blue were observed in deformed KBr at 10 and 80°K. The observed anomalies can be removed by a short annealing near 525°K. Both the dichroic behavior of the beta band and the energy shift of the $F$ band are consistent with the hypothesis that the source of vacancies is the edge-dislocation dipoles from plastic deformation. The $F$ centers formed upon ${\mathrm{Co}}^{60}$ irradiation of deformed KBr are most probably located a few Burgers vectors away from the core of one member of the edge-dislocation dipole inthe compression region, a fraction of an interatomic spacing above the slip plane where the edge dislocation is situated.