It was pointed out that Frenkel pair creation occurred in this halide via the interaction of a self-trapped exciton with a free exciton. This was confirmed by the dependence of the F center formation yield upon the 4th power of the dose rate. It was found that the F center production efficiency was increased, and the Vk center decreased, upon increasing the temperature from 77 to 300K. Each process had an associated activation energy of 0.028eV. The lifetime of the self-trapped exciton at room temperature was about 0.7s. It was noted that 2 types of Frenkel defect could be created as a result of the interaction of self-trapped excitons with free excitons. One of these was an F-H pair, and the other was an -I pair, where  was an anion vacancy and I was an interstitial atom. The present results supported the creation of the latter pairs during irradiation. No decay of absorption in the H band was observed at temperatures ranging from 77 to 140K, although the H centers were not stable at temperatures above 66K. The separation of the primary Frenkel pair was tentatively estimated to be equal to 4 lattice constants.

A.Flerov, V.Flerov: Materials Science Forum, 1997, 239-241, 599-602