HIGH-PERFORMANCE GLASS FOR THE DEEP-ULTRAVIOLET RANGE

Fluoride phosphate glasses are attractive candidates for high-performance glass for the deep ultraviolet range. The calculated values for the ultraviolet resonance wavelengths are comparable with those of CaF2, BeF2 and SiO2. However, the experimental ultraviolet transmission of glass is frequently limited by extrinsic absorption due to trace impurities, mainly transition metals. The influence of the redox states of Fe, Cu, Pb and Ni in the ppm range on the ultraviolet absorption was investigated. The individual absorption coefficients per ppm ion and the redox equilibria resulting from the melting conditions and refining temperature were determined. Fe3+, CU2+ and pb(2+) have the largest influence on the ultraviolet absorption. Glasses melted under reducing conditions have much higher ultraviolet transmission at 250 nm than glasses melted under oxidizing conditions. The ultraviolet absorption of the glass is strongly dependent on the reducing temperature. The ultraviolet absorption decreases and the luminescence increases drastically with increasing reducing temperature from 850 to 1100 degrees C. The redox equilibria are shifted to Fe2+ and Cu+, over 1100 degrees C towards Cu-0 colloids too. The molar absorption coefficients in the ultraviolet range of the lower redox states are more than one order lower than those of the higher redox states.