Er3+ ions doped bismuthate glasses sensitized by Yb3+ ions for highly efficient 2.7 μm laser applications

► Up-conversion, near- and mid-infrared emission enhanced at the same time by Yb3+ ions. ► The optimized ratio for 2.7 μm emission in this Er3+/Yb3+ co-doped tungsten glasses is 0.2:1.0. ► Introduced Yb3+ ions promote the 2.7 μm emission by populating Er3+: 4I11/2 level. ► Up-conversion emission is increased by ESA from Er3+: 4I11/2 and 4I11/2 levels.