UV Transmission and radiation-induced defects in phosphate and fluoride–phosphate glasses

The relationship between intrinsic and extrinsic ultraviolet (UV) transmission and UV lamp- and laser radiation-induced defects produced in phosphate glasses has been investigated. The composition was varied from simple binary metaphosphate glasses (MPs) to multicomponent ultraphosphate glasses (UPs), which can be melted on a commercial scale, to small amounts of mono- and diphosphates in fluoroaluminate glasses. The effects of the structure-dependent band gap (intrinsic effect) and the Fe2+/Fe3+ and P5+/P3+/P0 concentration ratios (extrinsic effect) on the UV absorption, and on the formation and recombination of radiation-induced defects were studied. A correlation has been inferred with the optical basicity of the glass matrix. The kinetics of the photoionization of Fe2+ to (Fe2+)+ were measured and simulated. This process is single photon, whose rate depends on the phosphate content and increases with increasing phosphate content (increasing basicity). Single and two photon mechanisms were indicated by the excimer laser radiation forming electron and hole defect centers, which were attributed to phosphorus species based on their electron paramagnetic resonance spectra. These defects cause additional absorption bands in the UV-visible region. Differences were detected between phosphate and fluoroaluminate glasses with a phosphate content ⩽20 mol%. The fluoroaluminate glasses have the lowest optical basicity and are stable against UV radiation, but crystallize. The optical basicity increases, the crystallization tendency decreases, and the UV radiation-induced defects increase with increasing phosphate content.