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

The relationship between intrinsic and extrinsic ultraviolet (UV) transmiss ion and UV lamp- and laser radiation-induced defects produced in phosphate glasses has been investigated. The composition was varied from simple binar y 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-depe ndent band gap (intrinsic effect) and the Fe2+/Fe3+ and P5-/P3-/P-0 concent ration 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 kinet ics of the photoionization of Fe2+ to (Fe2+)(+) were measured and simulated . This process is single photon, whose rate depends on the phosphate conten t and increases with increasing phosphate content (increasing basicity). Si ngle and two photon mechanisms were indicated by the excimer laser radiatio n forming electron and hole defect centers, which were attributed to phosph orus species based on their electron paramagnetic resonance spectra. These defects cause additional absorption bands in the UV-visible region. Differe nces H-ere detected between phosphate and fluoroaluminate glasses with a ph osphate content less than or equal to 20 mol%, The fluoroaluminate glasses have the lowest optical basicity and are stable against UV radiation, but c rystallize. The optical basicity increases, the crystallization tendency de creases, and the UV radiation-induced defects increase with increasing phos phate content. (C) 2000 Elsevier Science B.V. All rights reserved.