Long lasting phosphorescence properties of Tb3+-activated reduced calcium aluminate glasses

A long lasting green phosphorescence was found in Tb3+-doped calcium aluminate glasses prepared under a strongly reducing atmosphere. An electron-trapped centre giving an EPR signal at g = 1.999, an analogue of the F+ centre in CaO, was induced by illumination with ultraviolet (uv) radiation and decayed slowly after the illumination was stopped. A partial oxidation of Tb3+ ions to Tb4+ ions by uv: illumination was observed. A mechanism of the long lasting phosphorescence was suggested to consist of recombination of an electron released thermally from the F+-like centre with the photo-oxidized Tb3+ (Tb4+).