Transient absorption of niobium states in photorefractive materials

The transient absorption due to electron polaron states in LiNbO 3 , KNbO 3 , SrTiO 3 -Nb and glasses containing alkali niobates has been studied. The electron polarons are suggested to be Nb 4+ ions in various oxygen environments in all these crystals. It is shown that the position of the absorption band depends on Nb environment. The recharging of niobium states is suggested to be responsible for a fraction of the transient absorption in the phosphate glasses. The disordered structure of these glasses can account for wide absorption bands.