UV transparency and structure of fluorophosphate glasses

Ultraviolet (UV) transparency and local structural environment of fluorophosphate glasses in the Ba(PO3)(2)-MgF2-CaF2-AlF3 system have been studied with increasing fluoride content (covering the whole compositional range) by infrared (IR) reflection spectroscopy (IRRS) in conjunction with P-31 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. UV cutoff of the glasses shifts towards longer wavelength with increasing fluoride up to similar to 36 mol%. IRRS spectra indicate a gradual increase in nonbridging oxygens (NBOs) in this region. According to P-31 MAS NMR spectra, it is due to the combined effects of gradual increase in Q(1) sites and P-O-Al bridges (increase in optical basicity). Beyond similar to 36 mol% fluoride content, the UV cutoff shifts towards shorter wavelength. It is attributed to decrease in NBOs or Q1 sites (decrease in optical basicity) as revealed in the IRRS and P-31 MAS NMR spectra, respectively. In this region, true partial role of the metal fluorides in controlling UV transparency has been found to contribute significantly as well. (C) 2002 Elsevier Science B.V. All rights reserved.