It was recalled that the absence of long-range order in the glass structure permitted the definition of only point defects in these materials. These were intrinsic defects (atomic-sized local deviations from short-range order), impurity defects (isolated impurity atoms or ions in the glass network) and intrinsic impurity defects (complexes which consisted of impurity atoms that were chemically bonded to one of the intrinsic defect atoms). The latter defects were characteristic of doped glasses. The presence of point defects in glasses introduced new spectroscopic properties into the solid materials. Defect generation, interaction and recombination reactions - which resulted from external influences - caused the changes in the spectroscopic properties.

A.R.Silins: Radiation Effects and Defects in Solids, 1995, 134, 7-10