Boosting STE and Nd3+ NIR Luminescence in Cs2AgInCl6 Double Perovskite via Na+/Bi3+‐Induced Local Structure Engineering

Abstract Currently, lanthanide (Ln 3+ ) doped Pb‐free double perovskites (DPs) suffer from competitive emissions of the self‐trapped exciton (STE) and Ln 3+ . Herein, a new type of Nd 3+ ‐doped Cs 2 AgInCl 6 DPs with Na + /Bi 3+ co‐alloying is developed. Benefiting from Na + /Bi 3+ ‐induced local structural modification, both STE broadband visible luminescence and Nd 3+ near‐infrared (NIR) emissions are boosted via free exciton sensitization. Specifically, a total 648‐fold enhancement in emitting intensities compared to the Na + /Bi 3+ ‐free counterpart is realized, with a significantly improved NIR photoluminescence quantum yield (PLQY) from 0.16% to 30.3%. First‐principles density functional theory calculations, Raman spectra, and steady/transient‐state PL spectra verify the modification of local site symmetry, breakdown of parity‐forbidden absorption, and reduction of electron‐phonon coupling via Na + /Bi 3+ doping. Finally, a compact vis–NIR broadband light‐emitting diode (LED) is designed by coupling the Na/Bi/Nd: Cs 2 AgInCl 6 DP with a commercial ultraviolet LED chip, which shows promising applications in spectroscopic analyses and multifunctional lighting.