This paper discusses, in some detail, the nature of colour centres induced by radiation in different borate, silicate and phosphate glasses; using optical and ESR techniques. The role of cerium and other multi valent ions in suppression of some of these centres and in studying their nature is also discussed. In most glasses, the visible induced absorption was associated with positive hole centres. However, at certain compositions, an electron trap centre which absorbs in the visible is also induced by radiation, and was associated with certain structural defects, e.g. a non-bridging oxygen ion vacancy neighbouring the alkali ions in diborate or disilicate glasses, Pb2+ ions (or other iso electronic ions) taking network modifying positions, or Ce3+ ions in relatively high concentrations.
