Semi-empirical computer simulations were made of O vacancies in the pure oxide. The material was modelled by using molecular clusters of various sizes and structures. It was found that the calculated positions of the absorption and luminescence bands of the neutral O vacancy were in satisfactory agreement with those of the O-deficient center which was detected in the pure oxide. The absorption and luminescence bands of the vacancy corresponded to the dipole-allowed 1-electron transitions between 2 localized states with levels in the energy gap. The lower level was doubly occupied, and the upper one was empty; due to the bonding and anti-bonding combination, respectively, of sp orbitals of two Si atoms which were adjacent to the vacant site.

V.B.Sulimov, V.O.Sokolov: Journal of Non-Crystalline Solids, 1995, 191[3], 260-80