Er3+-doped PbF2: Comparison between nanocrystals in glass-ceramics and bulk single crystals

An appropriate annealing of a GeO2–PbO–PbF2:ErF3 glass leads to the formation of a glass-ceramic, composed of Pb1−xErxF2+x nanosized crystallites dispersed throughout an amorphous oxide matrix. These nanocrystallites are compared to Er3+-doped PbF2 bulk single crystals. The influence of the annealing temperature on the glass-ceramics characteristics is thoroughly investigated. For several glass-ceramics resulting from different heat treatments, the quantity of crystallized PbF2, as well as the segregation of Er3+ ions into the crystallites, has been studied through two methods: first, the study of the crystallographic characteristics and second, the evolution of the optical properties. It was evidenced that, for a heat treatment over 365 °C, the whole PbF2:Er has completely crystallized and that the segregation of Er3+ ions into the crystallites was total. Strong interactions between Er3+ ions occur in the Pb1−xErxF2+x single and nanocrystals, promoting cross-relaxation processes, under 488-nm excitation, and favouring the 660- (red) and 810-nm emissions at the expense of the 550-nm (green) one.