Efficient near-infrared emission from lead-free ytterbium-doped cesium bismuth halide perovskites

Yb doping of Cs₃Bi₂Br₉ results in near-infrared luminescence with 14.5% quantum yield when excited with above bandgap photons. This emission decreases sharply when bandgap is reduced below twice the emission energy raising the possibility that the mechanism involves quantum cutting.