Broadband Emission‐Enabled Energy Transfer in Double Perovskites for Efficient Er ³⁺ ‐Driven Long‐Wavelength Near‐Infrared Optoelectronics

Abstract High‐efficiency near‐infrared (NIR) light‐emitting diodes (LEDs) operating in 800‐2000 nm spectral window are pivotal for advancing optical communication, biomedical imaging, and security sensing. Here, a strategy using double perovskite Cs 2 AgInCl 6 nanocrystals co‐doped with Bi 3+ , Yb 3+ , and heavily doped Er 3+ is demonstrated to achieve efficient long‐wavelength NIR emission. The double perovskite host with self‐trapped excitons (STEs) property serves as an energy reservoir for subsequent transfer to Er 3+ . Bi 3+ doping induces lattice distortion, enhancing STEs formation and breaking octahedral symmetry around Er 3+ to boost the 4 I 13/2 → 4 I 15/2 transition. Yb 3+ as a sensitizer, bridges the energy gap between STEs and Er 3+ , facilitating efficient energy transfer to populate Er 3+ metastable states. This synergistic mechanism, enabled by double perovskite's broadband emission and homovalent doping tolerance, allows heavy Er 3+ loading (≥20% molar‐ratio), driving a photoluminescence quantum yield of 31% at 1540 nm. NIR LEDs fabricated with these nanocrystals achieve a champion external quantum efficiency (EQE) of 1.79% at 1540 nm (average EQE: 1.49%) and maintain 50% emission intensity for 3.3 h under continuous operation. This work establishes double perovskites as a versatile platform for STEs‐mediated NIR emission, offering a new paradigm for designing high‐performance long‐wavelength optoelectronic devices.