Yb3+ sensitized Mo3+ spin-flip luminescence through downconversion and upconversion in halide perovskites.

Mo3+-activated halide perovskites can exhibit narrowband spin-flip luminescence through downconversion and upconversion. However, because Mo3+ absorbs weakly in the near-infrared (NIR) region, NIR excitation generally produces only weak room-temperature Mo3+ downconversion emission and Mo3+ upconversion emission only at low temperatures. Here, we demonstrate that Yb3+ effectively sensitizes Mo3+ in Cs2NaInCl6 double perovskites. Under 920-nm excitation, Yb3+ → Mo3+ energy transfer markedly enhances the 1095-nm Mo3+ spin-flip emission. This sensitization also enables, to the best of our knowledge, the first room-temperature observations of both 1850-nm NIR emission arising from the 2T2g → 2Eg/2T1g inter-excited-state transition and 700-nm Mo3+ upconversion emission. Our work establishes Yb3+ sensitization as an effective strategy for accessing NIR-excited, room-temperature Mo3+-centered emission bands in halide perovskites.