Sol–gel preparation and white up-conversion luminescence in rare-earth doped PbF2 nanocrystals dissolved in silica glass

89.5(SiO2)10(PbF2)0.5(REF3) silicate glasses have been prepared using room temperature sol–gel processing of Si(OCH2CH3)4, Pb(CH3COO)2·3H2O, RE(CH3COO)3·nH2O and trifluoroacetic acid as a fluorinating agent, where RE stands for rare-earth ions, such as Yb3+, Er3+, Ho3+, Tm3+, or combinations of those ions. On heat treatment of these glasses at about 300–400 °C, the rare-earth doped spherical PbF2 nanocrystals precipitate within SiO2 glass matrix providing transparent nano-structured glass–ceramics, while the diameter of the nanocrystals can be set in the range from 5 to 25 nm by varying time and temperature of the heat treatment. The structural and photoluminescence studies confirm the incorporation of rare-earth ions into the PbF2 nanocrystals and white and tuneable colour up-conversion luminescence has been detected in case of Yb3+-Er3+-Tm3+ and Yb3+-Ho3+-Tm3+ co-doped nanocrystals by varying dopant ratio and pump power.