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

In this paper, the electronic properties of localized states in wide-gap oxide glasses such as sodium silicate, sodium germanate, lead silicate, 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 determine localized states in these glasses. The corresponding data for crystals of these materials were used for comparison. The spectrum of localized states is determined by many different types of a short-range order in the glass structure. In the glasses studied the localized states create an ensemble of structurally non-equivalent anisotropic luminescence centers. Their concentration is on the level of 1%. These states 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 localized states into defects.