Fluorescence investigation of Ho3+ in Yb3+ sensitized mixed-alkali bismuth gallate glasses

Efficient 2.0 μm infrared and visible upconversion emissions have been observed in Ho3+/Yb3+ co-doped mixed-alkali bismuth gallate (LKBBG) glasses having a maximum-phonon energy of 673 cm−1. The Judd–Ofelt parameters Ω2, Ω4 and Ω6 of Ho3+ indicate that there is a high asymmetry and strong covalent environment in LKBBG glasses. The large absorption and emission cross-sections of Yb3+ confirm that it is a suitable sensitizer for capturing and transferring pump energy to Ho3+. The emission cross-section profile for the 5I7 → 5I8 transition is derived using the reciprocity method and the peak value is 5.54 × 10−21 cm2, which is much larger than the value in fluorozircoaluminate glasses. LKBBG glasses exhibit low maximum-phonon energy and large refractive index, and it is possible to achieve an effective 1.66 μm U-band emission of Ho3+ under 900nm laser radiation.