Boosting NIR-Driven Photocatalytic Activity of BiOBr:Yb³⁺/Er³⁺/Ho³⁺ Nanosheets by Enhanced Green Upconversion Emissions via Energy Transfer from Er³⁺ to Ho³⁺ Ions

Exploiting near-infrared (NIR) light responsive photocatalysts is especially significant for effective use of solar energy. Enhancing the luminescence of upconversion (UC) photocatalysts is particularly important for the development of NIR-driven photocatalysts. Here, Yb³⁺/Er³⁺/Ho³⁺ triple-doped BiOBr nanosheets were synthesized by solvothermal method. The UC luminescence and NIR photocatalytic activity of BiOBr:Yb³⁺/Er³⁺/Ho³⁺ nanosheets can be optimized by tuning the Ho³⁺ doping concentrations. Results indicated that the green UC emission intensity of BiOBr:Yb³⁺/Er³⁺/0.5%Ho³⁺(BYE-0.5Ho) was improved by about 4.2 times that of BiOBr:Yb³⁺/Er³⁺(BYE-0Ho). Based on the UC spectra and lifetime decay curves, the energy transfer of Er³⁺ → Ho³⁺ was the main factor responsible for the enhanced green UC luminescence. As expected, the BYE-0.5Ho demonstrated superior photocatalytic performance in degrading RhB under NIR light irradiation, which was 1.53 times higher than that of BYE-0Ho. Moreover, this superior photoactivity can achieve the degradation of MB and BPA, verifying the universal applicability of BiOBr:Yb³⁺/Er³⁺/Ho³⁺ nanosheets. In depth investigations confirmed that the improving activity can be ascribed to enhanced green UC luminescence and improved the separation efficiency of the electron–hole pairs through doping Ho³⁺ ions, as evidenced by photoluminescence and electrochemical analyses. This work provides an effective way of enhancing NIR photocatalytic performance, which will be conducive to making full use of solar energy in the future.