UV transparency and structure of fluorophosphate glasses

Abstract

Ultraviolet (UV) transparency and local structural environment of fluorophosphate glasses in the Ba(PO 3) 2–MgF 2–CaF 2–AlF 3 system have been studied with increasing fluoride content (covering the whole compositional range) by infrared (IR) reflection spectroscopy (IRRS) in conjunction with 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. UV cutoff of the glasses shifts towards longer wavelength with increasing fluoride up to ∼36 mol%. IRRS spectra indicate a gradual increase in nonbridging oxygens (NBOs) in this region. According to 31P 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 ∼36 mol% fluoride content, the UV cutoff shifts towards shorter wavelength. It is attributed to decrease in NBOs or Q 1 sites (decrease in optical basicity) as revealed in the IRRS and 31P 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.