Effect of oxygen substitution by halide ions on structure, thermal stability and upconversion fluorescence in Er3+/Yb3+-codoped germanium–bismuth glasses

For the first time, effect of halide ions (F−, Cl−, Br−, and I−) introduction on structure, thermal stability, and upconversion fluorescence in Er3+/Yb3+-codoped oxide–halide germanium–bismuth glasses has been systematically investigated. The results show that halide ions modified germanium–bismuth glasses have lower maximum phonon energy and phonon density, worse thermal stability, longer measured lifetimes of 4I11/2 level, and stronger upconversion emission than germanium–bismuth glass. All these results indicate that halide ions play an important role in the formation of glass network, and have an important influence on the upconversion luminescence. The possible upconversion mechanisms of Er3+ ion are also evaluated.