Abstract
Efficient 2.0 μm infrared and visible upconversion emissions have been observed in Ho 3+/Yb 3+ co-doped mixed-alkali bismuth gallate (LKBBG) glasses having a maximum-phonon energy of 673 cm −1. The Judd–Ofelt parameters Ω 2, Ω 4 and Ω 6 of Ho 3+ indicate that there is a high asymmetry and strong covalent environment in LKBBG glasses. The large absorption and emission cross-sections of Yb 3+ confirm that it is a suitable sensitizer for capturing and transferring pump energy to Ho 3+. The emission cross-section profile for the 5I 7 → 5I 8 transition is derived using the reciprocity method and the peak value is 5.54 × 10 −21 cm 2, 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 Ho 3+ under 900nm laser radiation.
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