Nanocrystals precipitation and up-conversion luminescence in Yb3+-Tm3+ co-doped oxyfluoride glasses

Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·(4.8–x) GdF3·0.1NdF3·xYbF3·0.1TmF3 (x=0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8) in molar ratio was developed. When the oxyfluoride glasses were heat-treated at the first crystallization temperature, the glasses gave transparent glass-ceramics in which rare earth containing fluorite-type nanocrystals of about 17.2 nm in diameter uniformly precipitated in the glass matrix. Compared with the glasses before heat treatment, the glass-ceramics exhibited very strong blue up-conversion luminescence under 800 nm light excitation. Rare earth containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass, the size of precipitated nanocrystals could be controlled by laser power and scan speed. The intensity of the blue up-conversion luminescence was strongly dependent on the precipitation of β-PbF2 nanocrystal and the YbF3 concentration. The reasons for the highly efficient Tm3+ up-conversion luminescence after laser irradiation were discussed.