Photothermal Creation of Cu°v a + Centres and Mobility of Anion Vacancies in X‐Irradiated KCl:Cu Crystals

Associates of Cu° atoms with anion vacancies v   a +(Cu°v   a + centres) are used as luminescent detectors for the study of anion vacancy mobility in KCl crystals. It is found that near 220 K, Cu°v   a +centres may be thermally formed because of the migration of v   a +only to its neighbouring Cu° atom (i.e. the process occurs in {Cu°–v   a − } pairs). An analogous process in {Cu + –v   a + } pairs results in the creation of Cu + v   a +centres. After Cu + v   a +have trapped electrons released at the thermal destruction of Cu°, Cu°v   a +centres are formed. {Cu + –v   a + } and {Cu + –v   a + } pairs are produced at low temperatures by the transfer of an F electron onto an impurity ion in irradiation‐generated {Cu + –F} and {Cu 2+ –F} pairs. If the crystal contains Cu   a −centres, Cu°v   a +centres may be formed at T > 370 K by the interaction of mobile V F centres, produced at a thermal dissociation of Cl 3 molecular ions, with Cu   a −centres. It is proposed that at T < 300 K it is not the isolated but the “associated” anion vacancy that can migrate. This process occurs in the field of some defects and needs a comparatively lower activation energy than the motion of isolated v   a + . The isolated or “free” v   a +which are believed to be mobile at higher temperatures, are practically absent in X‐irradiated crystals at T > 250 K due to the interaction of v   a +with mobile cation vacancies or interstitial halide ions as well as due to the thermal association of v   a +with neighbouring lattice defects.