The molecular statics method was used to determine the energies and configurations of vacancy/di-vacancy interactions in crystals. It was shown that a high level of local vacancy supersaturation permitted the possibility of cluster formation. The study of carrier traps by means of luminescence methods was used to reveal vacancy clusters. The results confirmed that the interaction of vacancies in alkali halide crystals was rather complex. The approach of defects to within a distance of about one lattice spacing required the surmounting of a barrier. The height of the barrier which had to be surmounted, for the linking of vacancies, defined the degree of stability of vacancy centers; which were essentially metastable formations. Thermoluminescence investigations of KCl crystals, with a high content of excess vacancies, revealed a slight net accumulation. A non-elementary spectrum of high-temperature thermoluminescence peaks indicated the existence of a range of stable cluster forms.

A.V.Gektin, V.J.Serebryanny, N.V.Shiran: Radiation Effects and Defects in Solids,

1995,134, 411-5