Refractive index changes in photochromic SbPO4-WO3 glass by exposure to band-gap radiation

We report photoinduced photo-darkening in SbPO4-WO3 glass by exposure to 532nm light with a power density of 143mW/cm2. The time of exposure was varied between 0 and 256min following which visible photo-darkening, peaking at 850nm was observed. Spectrophotometer measurement of absorption was performed for both treated and untreated regions of the sample. Time exposure to below band-gap light results in a single exponent Gaussian absorption function over an exceptionally wide range of wavelengths (500nm-1600nm), with a 1/e width of 647.5nm. Kramers-Kronig transform of the change in the absorption indicates a negative local change in the refractive index. The dispersed refractive index change at 1550nm, a Delta , is calculated to be a arrow right 4a degree 5A-10a closed integral #14 6; 8. The peak absorption increases with time of exposure and the photo-darkening remains irreversible at room temperature.