Trace Doping Enhanced Near‐Infrared Emission in Cs ₂ MnCl ₄ for Anti‐Interference Optical Communication

Near‐infrared (NIR) emitters are essential for night‐vision imaging and interference‐resilient optical wireless communication yet engineering efficient NIR emission in Mn‐based metal halides remains challenging due to the sensitivity of Mn–Mn pair centers to local structure and defects. Here, a hydrothermal synthesis of Cs 2 MnCl 4 single crystals exhibiting a broadband NIR emission (700–900 nm, 780 nm peak) from Mn–Mn coupled centers is reported. Bi 3+ dopant engineering introduces an additional UV excitation channel and locally perturbs the host lattice, shifting the emission balance toward Mn–Mn pair centers while suppressing the visible monomer Mn 2+ channel, and boosting the photoluminescence quantum yield from 3% for pristine Cs 2 MnCl 4% to 19% for Cs 2 MnCl 4 :Bi. A phosphor‐converted LED prototype delivers broadband NIR electroluminescence for night‐vision imaging, and a proof‐of‐concept optical link maintains clear image transmission under strong indoor lighting interference. These results demonstrate that trace Bi doping effectively tunes Mn–Mn‐coupled NIR emission and improves the applicability of Mn‐based halide phosphors in NIR imaging and indoor optical communication.