Ionic and electronic processes during frenkel defect annealing in KBr crystals above LHeT

Abstract

The relaxation of radiation‐induced optical absorption spectra and a set of thermally stimulated curves (current, depolarization current, diffusion current, emission‐desorption of gas, thermal bleaching) of KBr crystals X‐irradiated at 4.6 K are recorded synchronously or step by step. A multistage annealing of defects is detected: (i) from 4.6 to 32 K about ten substages controlled by the I centre delocalization are accompanied by electron and energy release, (ii) from 32 to 60 K about six substages controlled by the H, centre delocalization are accompanied by corresponding electron and energy release and gas desorption peaks. A recombination of the migrating I or H centres within such complementary defect systems (pairs, triplets et al.) takes place: (i) {I…α}, {I… F… Vk}, {I… F'… Vk… Vk}, (ii) {H… F} and {H… F'… Vk}. Following phenomena in KBr at 4.6 K are observed and discussed: (i) the “F‐photostimulated” electron tunneling transfer within the excited pair {F* γ. HA} → (α… IA}, (ii) the effect of dc field (3kV/cm) caused Frenkel defect formation efficiency increase (by ≧ 10%), (iii) the photoelectrical dissociation of the α centres. Comments about the anion Frenkel primary defect generation mechanisms are made.