UV radiation effects in fluoride phosphate glasses

Fluoride phosphate glasses are attractive candidates as ultraviolet-transmitting materials. It is important to know their resistance to radiation damage by excimer laser illumination. One fluoride phosphate glass (35 AlF3, 30 CaF2, 15 SrF2, 10 MgF2, 10 Sr(PO3)(2) (mol%)) of high purity and doped with metal ions, Fe, Cu, Ce, Pb, was irradiated by excimer laser illumination at 193 and 248 nm. The samples were melted under oxidizing, normal and reducing conditions to change the redox state of the doped ions. Absorption and fluorescence spectra of the samples were measured before and after irradiation. From the radiation-induced changes in the absorption and fluorescence spectra, the following conclusions were obtained. Irradiation induces a photo-oxidation of the lower valence ions. The formation of hole centers is suppressed in samples doped with Fe and with 1000 ppm Ce, respectively, but it is intensified in samples doped with Pb, Cu and Ce up to 100 ppm. The formation of electron centers depends on the concentration of lower valence ions before irradiation. The radiation-induced effects are strong if the wavelength of the excimer laser radiation is in the range of strong absorption bands of the lower valence ions.