Surface-luminescence from thermally reduced bismuth-doped sodium aluminosilicate glasses

We report on the effect of hydrogen annealing on the optical properties of bismuth-doped sodium aluminosilicate glasses. The redox state of bismuth in the as-melted glasses is governed by the composition, viz., NIR luminescence is observed only in the glasses with low optical basicity. Upon thermal reduction, visible emission from Bi3+ and, eventually, minor amounts of Bi2+ is significantly lowered, depending on heat-treatment time and temperature, and glass composition. Hydrogen treatment was also found to result in a decrease of the NIR emission intensity and, at the same time, formation of metallic bismuth particles in the surface region. Surface-tinting as well as the decrease of visible luminescence follow Arrhenian kinetics, suggesting that hydrogen permeation is the rate-governing process. Upon re-annealing in air, the effects of thermal reduction on the optical properties are reversible only to a limited extent.