UV-absorption and radiation effects in different glasses doped with iron and tin in the ppm range

Abstract

Intrinsic and extrinsic ultraviolet absorption and radiation-induced effects were investigated in different glass types, fluorides, phosphates and borosilicates. High-purity glass samples were prepared and their intrinsic absorption was measured in the vacuum ultraviolet region. The influence of doped iron and tin species in the ppm range on the ultraviolet absorption and radiation-induced effects were studied. The maximum of the dominating Fe 3+ charge transfer band has the lowest energy (4.8 eV) and intensity in the fluoride glass and the highest energy (5.6 eV) and intensity in the borosilicate glass samples. The charge-transfer band for Fe 2+ has much lower intensity and higher energy (∼5.7 eV) than those for Fe 3+ in all glasses investigated. Photo-oxidation of Fe 2+ to (Fe 2+) + hole centres and glass-matrix-related electron centres by UV irradiation increases the UV absorption drastically in all glasses. The kinetics was measured and simulated depending on the glass matrix. In fluoride and phosphate glasses, Fe 3+ complexes are very stable against UV irradiation and do not participate in UV-radiation-induced processes. Only in silicate glasses, Fe 3+ is able to form a (Fe 3+) – electron centre defect which decreases the charge transfer absorption of Fe 3+ near 220 nm, but increase the absorption of hole centre defects, with a maximum at 280 nm. So, the defect generation in the ultraviolet region increases drastically with increasing Fe content in the range 10–200 ppm. Three or four electronic s → p transitions for Sn 2+ were detected by optical absorption and luminescence spectroscopy shifted to longer wavelength in the range fluoride → phosphate → silicate glass samples. Sn 4+ absorption bands were found at shorter wavelength in the vacuum ultraviolet region in all cases investigated. Sn 2+ ions are photo-oxidised under UV radiation very fast, which leads to an decrease of absorption near 200 nm and to an increase near 250 nm. Both Sn 2+ and Sn 4+ are involved in the radiation-induced processes. In contrast to phosphate and silicate glasses, tin-doped fluoride glasses are very resistant against UV lamp but not against UV laser irradiation. The mechanisms are very complicated, with maximums and minimums in the defect formation curves.