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

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 lambda = 325 nm (E-ex = 3.815 eV) an enhancement of more than two orders of magnitude for broad white emission centered at about E-em approximate to 23 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. (C) 2016 Elsevier B.V. All rights reserved.