Enhancement of Yb³⁺ Emission in Bi₃TeBO₉ through Efficient Energy Transfer from Bi³⁺ Ions

An efficient near-infrared emission of Yb3+ ions sensitized by Bi3+ ions was revealed in Bi3TeBO9:Yb3+ microcrystalline powders. Bi3TeBO9:Yb3+ doped with different concentrations of Yb3+ ions (0.5, 1.0, 2.5, 4.0, and 7.5 at %) were synthesized by means of the modified Pechini method. The structure, morphology, and elemental composition of samples were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques. The μ-Raman spectroscopic measurements of Bi3TeBO9:Yb3+ allowed us to determine the energy vibrations of characteristic molecular groups BO3 and TeO6 present in the Bi3TeBO9 matrix. Emissions of Bi3TeBO9:Yb3+ powders were measured upon excitation at 330 nm by Bi3+ ions (the 1S0 → 3P1 transition) in VIS (Bi3+ ions emission assigned to the 3P0 → 1S0 transition) and NIR (Yb3+ ions emission assigned to the 2F5/2 → 2F7/2) spectral ranges. In particular, the strongest emission band of Yb3+ ions at 975 nm was observed in the spectrum of Bi3TeBO9:Yb3+ doped with 4.0 at % of Yb3+ ions. This suggests that Bi3+ ions present in the Bi3TeBO9 matrix can be used as a UV absorption sensitizer for Yb3+ ions in the considered systems. Moreover, the decay times of 3P0 → 1S0 transitions of Bi3+ ions (emission in VIS with maximum at 550 nm) and 2F5/2 → 2F7/2 transitions of Yb3+ ions (emission in NIR at 975 nm) upon excitation at 330 nm were measured. The calculated energy transfer efficiency and quantum efficiency coefficients confirmed the effective energy transfer from Bi3+ to Yb3+ ions in the Bi3TeBO9:Yb3+ system. The obtained results show that Bi3TeBO9:Yb3+ powders, as efficient UV to NIR spectral converters, can be potentially used in c-Si solar cell technology, enhancing the photovoltaic effect.