Non-bridging oxygen dependent redox and spectroscopic properties of Cu species in phosphosilicate glasses

• At low doping, extra Cu+ tends to be reduced into Cu0 in phosphosilicate glasses.
• At high doping, extra Cu+ tends to be oxided into Cu2+ in phosphosilicate glasses.
• The oxidation of Cu+ → Cu2+ is due to the increasing of non-bridging oxygen.
• Energy transfers from Cu+ to Cu2+ are primary quenching routes of the Cu+ PL.
• Different Cu+ cites were revealed as [CuO6] octahedrons with tetragonal or trigonal ​ distortions.

We reported a series of phosphosilicate glasses containing different Cu species (Cu0, Cu+ and Cu2+). With X-ray diffraction (XRD), Transmission electron telescope (TEM), and absorption spectra (UV–Vis), Cu0 NPs and Cu+ were identified in the glasses with low Cu concentrations (0.02; 0.04; 0.1 mol%), and Cu+ and Cu2+ were identified in the glasses with high Cu concentrations (0.2; 0.4; 0.6 mol%). Raman spectra gave a clue that the quantity of non-bridged oxygens were related with the oxidation of Cu+ → Cu2+ at high Cu concentration. With photoluminescence spectra(PL) and time resolved decay spectra, different Cu+ sites were discovered with octahedral coordination predominantly with different tetragonal distortions, and ETs from Cu+ to Cu2+ were also revealed with proposed mechanisms. The study in understanding the structural effect of Cu-doped glass on luminescence would be an important step towards the rational design of transition metal doped luminescent glasses for various applications.