Near- and mid-infrared photoluminescence in Ho3+ doped and Ho3+-Yb3+ codoped low-phonon-energy germanotellurite glasses

► Ho3+ 1.20 μm emission (5I6→5I8 transition) was observed in Ho3+-Yb3+ codoped fiber. ► Incorporation of Yb3+ increases the quantum efficiency of Ho3+ 1.20 μm emission. ► Low phonon energy of the host contributes to Ho3+ 1.20 and 1.38 μm emissions. ► Judd-Ofelt analysis indicates strong asymmetry and covalent environment of Ho3+.