Annealing of Vk-type centres in mixed KBr-KI crystals

The annealing of IBr- and I2-Vk-type centres in mixed KBr-KI crystals with varying iodine concentration has been investigated by the fractional glow technique. It is shown that for an I- concentration exceeding 1-5 mol.% the hole delocalisation from iodine monomers and dimers is characterised by both a reduced activation energy and a reduced annealing temperature. The kinetics of the corresponding thermoactivated recombination process reveals clearly a diffusion-controlled behaviour. A new mechanism of hole migration through chains of spatially separated iodine impurities is proposed.