Exciton Trapping and Cascade Energy Transfer Enable Highly Efficient Near‐Infrared Electroluminescence in Rare Earth Based Perovskite

Lead‐free rare‐earth‐based halide perovskite have emerged as a promising candidate for near‐infrared light‐emitting diodes (NIR‐LED), yet their development has been hindered by inefficient energy transfer and severe non‐radiative losses. Here, we report a comprehensive optimization strategy for Cs 3 YbBr 6 :Er 3+ nanocrystals through Sb 3+ sensitization and niacin passivation, achieving record‐breaking electroluminescence performance. Systematic investigations reveal that Yb 3+ serves as a critical energy transfer bridge, with optimal 5% Er 3+ doping yielding a PLQY of 20.34% at 1540 nm. The introduction of Sb 3+ as an efficient sensitizer captures free exciton and enhances energy transfer, boosting the 1540 nm PLQY to 36.6%. First‐principles calculations demonstrate that Sb 3+ incorporation reduces the bandgap and promotes charge localization around [SbBr 6 ] 3− octahedra. Furthermore, niacin molecules selectively passivate undercoordinated Yb 3+ sites via carboxyl coordination, reducing film roughness, decreasing trap densities, and achieving balanced carrier mobilities. The resulting LED exhibits multi‐wavelength emissions, peaking at 470 nm, 980 and 1540 nm, respectively. It demonstrates an external quantum efficiency of 9.96% and exceptional operational stability of 753 min (T 50 ), representing the highest efficiency reported for various rare‐earth‐based perovskite LEDs. A practical infrared imaging system is successfully demonstrated, highlighting the potential of this materials platform for next‐generation optoelectronic applications.