Unveiling self‐trapped exciton emission in lanthanide‐doped Cs ₂ NaInCl ₆ double perovskites for efficient white LEDs

Abstract Lead‐free halide double perovskite‐based white light‐emitting diodes (WLEDs) have recently emerged as promising candidates for advanced lighting technologies. However, their inherent characteristics, such as indirect bandgaps and forbidden electronic transitions, significantly limit photoluminescence (PL) efficiency, posing critical challenges to their widespread application. Herein, we selected highly efficient blue‐emitting Cs 2 NaInCl 6 :Bi 3+ nanocrystals (NCs) as a matrix, into which lanthanide ions (Ln 3+ ) were incorporated by ion doping, yielding a series of Ln 3+ ‐doped perovskite NCs, Cs 2 NaInCl 6 :Bi 3+ ,Ln 3+ (Ln 3+ = Eu 3+ , Tb 3+ and Dy 3+ ), with an impressive photoluminescence quantum yield (PLQY) of 85.1%. Doping with Ln 3+ effectively regulates the optical bandgap and PL efficiency of these materials. Femtosecond transient absorption (fs‐TA) spectroscopy reveals changes in self‐trapped exciton (STE) dynamics and reduced deep trap‐related states upon Ln 3+ doping, indicating effective modulation of self‐trapping and defect passivation. The lead‐free halide double perovskite‐based WLED devices were demonstrated by coating the highly fluorescent green‐emissive Cs 2 NaInCl 6 :Bi 3+ ,Tb 3+ NCs with red‐emitting (Sr, Ca)AlSiN 3 :Eu phosphor on a commercial ultraviolet (UV) chip, achieving a color‐rendering index (CRI) of 87.5 and a correlated color temperature (CCT) of 5723 K. This study is laying a theoretical foundation for the regulation of the optical properties of lead‐free halide double‐perovskite NCs and defining an ideal model for the development of efficient WLEDs.