LOCALIZED STATES IN WIDE-GAP GLASSES - COMPARISON WITH RELEVANT CRYSTALS

In this paper, the electronic properties of localized states in wide-g ap oxide glasses such as sodium silicate, sodium germanate, lead silic ate, silica and germania are reviewed. Experimental spectroscopic data (optical absorption, as well as luminescence and its excitation) and luminescence decay kinetics at different temperatures were used to det ermine localized states in these glasses. The corresponding data for c rystals of these materials were used for comparison. The spectrum of l ocalized states is determined by many different types of a short-range order in the glass structure. In the glasses studied the localized st ates create an ensemble of structurally non-equivalent anisotropic lum inescence centers. Their concentration is on the level of 1%. These st ates disappear after glass crystallization. The structural elements of localized states are the precursors of radiation-induced defects. In the case of silica, the optical absorption of the precursor is covered by the excitonic absorption band. Reducing conditions transform the l ocalized states into defects.