Modulation of single-band red upconversion luminescence in Er3+/Yb3+ codoped bismuth oxyiodide nanoplates by bandgap engineering and their application in NIR photocatalysis

In this work, we report a facile strategy to obtain the single-band red upconversion (UC) luminescence of Er3+ by the tunable bandgap of the host. The Er3+/Yb3+ codoped bismuth oxyiodide (BiOI, Bi4O5I2, Bi5O7I) with different bandgap are synthesized via in situ calcination of BiOI. Theoretical and experimental results indicate the bandgap is tuned from 1.86 to 3.13 eV in the calcination process from the original the Bi/I ratio changing. Through the bandgap engineering, the Bi4O5I2:Yb3+/Er3+ exhibits intense single-band red emission, due to its bandgap of 2.39 eV, can effectively absorb the green UC emission to generate e(-)/h(+) pairs under NIR irradiation, which is confirmed by the degradation of RhB under NIR light irradiation. Furthermore, the UC luminescence and NIR photocatalytic activity of Bi4O5I2: Yb3+/Er3+ can be optimized by modulating the doping concentration of the Yb3+. The Bi4O5I2:6%Yb3+/Er3+ exhibits the strongest red emission and the superior photocatalytic performance in degrading BPA under NIR light irradiation. This research suggests an effective way to realizing single-band red emitters by bandgap engineering and demonstrates Er3+/Yb3+ codoped appropriate bandgap bismuth oxyiodide could be potential application in NIR-responsive UC photocatalysts.