Absorption phenomena in multicomponent phosphate glasses with Mn

Abstract

The absorption and ESR spectra of multicomponent alumino-phosphate glasses doped with manganese (0·2–20 mol %) has been measured and compared with the absorption spectra of manganous and manganic ions in model solutions. The unirradiated glasses show in ultraviolet region increasing absorption below 200 nm with the shoulder at 235 nm and the absorption bands due to manganous oxygen complexes in octahedral symmetry. They are similar to the absorption bands of Mn2+ in concentrated H3PO4 acid. In irradiated glasses the bands at 200, 235, 275 (only if Mn is present) and a broad band at 540 nm appear. After the annealing at 450 C all radiation-induced bands disappear and the bands at 235 nm is more pronounced. The Mn3+ in H3PO4 solution exhibit the absorption spectrum with a weak band at 530 nm and a very intense band at 270 nm. It is therefore proposed that both the 540 and 275 nm bands in irradiated glasses can be assigned to octahedral oxygen complexes of Mn3+, i.e. to hole centres. The band at 200 nm which is practically independent of the modifiers (Be, Mg, Ca, Sr and Ba) is, therefore, associated with electron centres (electrons trapped in non-bridging oxygen vacancies). It is suggested that the band at 235 nm in irradiated and annealed glasses is associated with irreversible structural changes.