Fabrication and photochromic properties of Al2O3–CaO binary glasses

Abstract The effects of preparation atmosphere on the formation and Photochromic properties of Al2O3 -CaO system glass were investigated. A reducing atmosphere was conducive to the formation of glasses with high Al contents, whereas an air atmosphere was favorable for the formation of glasses with low Al contents. Glasses fabricated under a reducing atmosphere exhibited a higher darkening degree than those fabricated under an air atmosphere, and their darkening degree increased with increasing Al content. The optimal irradiation wavelength for darkening was approximately 250 nm. The darkening faded slowly at room temperature and rapidly after heat treatment at above 200 °C. Moreover, the darkened glass faded completely after irradiation with blue-violet light (wavelength of 390–410 nm) for 10 min. A photochromic mechanism was suggested based on the results of absorption spectrum and electron spin resonance.