Semi-empirical quantum chemical simulations of 125-atom clusters have been undertaken to obtain the self-consistent atomic and electronic structure of the two basic electron defects in MgO crystals — F+ and F centers (one and two electrons trapped by an O vacancy). The calculated absorption and luminescence energies agree well with the experimental data, the excited states of both defects are found to be essentially delocalized over nearest-neighbour cations. The mechanism of the F+ → F photoconversion is discussed.
Computational Materials Science, Volume 5, 1996, Pages 298-306

Abstract. The influence of overstoichiometric Cdi atoms on the optical properties of cadmium iodide layered crystals has been investigated. The results of optical absorption, luminescence, and luminescence excitation studies of CdI2 crystals with controlled deviation from stoichiometric composition allow observing correlations between the Cdi concentration and features in absorption and emission spectra up to concentrations of 10#18 cm−3. At higher concentrations the overstoichiometric cadmium atoms form clusters, which were observed using scanning electron microscopy. The extinction spectra of (CdIi)n clusters are calculated in the frame of Mie theory and are found to correlate with the optical studies.
J. Phys.: Condens. Matter 19 (2007) 395015 (9pp)