Infrared tuneable up-conversion phosphor based on Er3+-doped nano-glass-ceramics

Up-conversion luminescence has been studied in the Er3+-doped oxyfluoride glass, its daughter nano-glass-ceramics and the polycrystalline ErF3 when excited at infrared wavelengths of either 800 or 980 nm. The mechanism of the up-conversion luminescence is shown to differ for excitations at 800 and 980 nm since the different excited levels of the Er3+ are involved, respectively. An order of magnitude increase of red-to-green up-conversion luminescence ratio has been observed with nano-ceramming of the precursor glass when excited at 800 nm and a full dominance of the red up-conversion luminescence has been observed in the ErF3 at the both excitation wavelengths. Observed changes in the spectra of the up-conversion luminescence from the precursor glass to its daughter nano-glass-ceramics provide a tool for tuning the colour of the up-conversion luminescence by ceramming of the precursor glass. These changes are shown to be due to decrease of the vibration energy of phonons coupled to the Er3+ ions embedded to the PbF2 nano-crystals with nano-ceramming. Hence we report for the first time that the red up-conversion luminescence from the Er3+-doped material can be due to the radiative transition 4F5/2, 4F3/2 → 4I13/2 of the Er3+ ion, which is principally allowed only in such a low-phonon energy host as the PbF2 nano-crystals, while such red up-conversion luminescence is almost completely non-radiatively quenched in the oxyfluoride precursor glass. The up-conversion emission spectrum of the ErF3 is dominated by a cross-relaxation mechanism typical of hosts with a very high doping level of the Er3+ ions.