Optical modifications at the intrinsic absorption threshold in soda lime silicate glass by Ag+–Na+ ion exchange

Abstract Silicate glass slides with different alkali metal and alkaline earth metal content were doped with different amounts of silver by Ag+–Na+ ion exchange in order to obtain glass showing strong luminescence in the visible spectral range suitable for solar glass or UV-LED-lenses. After excitation at λ = 325 nm (Eex = 3.815 eV) an enhancement of more than two orders of magnitude for broad white emission centered at about Eem ≈ 2.3 eV is achieved. Modifications of doped glass are investigated by absorption spectrophotometry for monitoring the intrinsic absorption threshold and by polarized photoluminescence spectroscopy for evaluating the enhanced emissions. The luminescence enhancement requires a modification of the intrinsic absorption threshold due to a decreased optical band gap. This is explained by a locally driven redox-reaction, which also should form at least one reduced silver containing species. The formed bright intra-ionic luminescence center creates a structure with at least three energy levels. This center is assumed to be closely related with the band structure and should cause a creation of holes, electrons or one of their bound states like excitons or polarons.