Achieving Nearly Quantitative (∼100%) IQE and 42.3% EQE Across NIR‐I and NIR‐II Regions with Cr3+‐doped Cs2NaScCl6 under 300 nm Excitation

Abstract Lead‐free rare‐earth‐based perovskites have received widespread attention for their unique optical properties, although achieving efficient broadband near‐infrared (NIR) emission with these materials remains a challenge. Here the synthesis of a rare earth‐based double perovskite (Cs 2 NaScCl 6 ) by an improved solid phase method is reported. The doping of Cr 3+ led to the formation of [CrCl 6 ] 3− octahedron, which exhibited a broadband NIR emission peaked at 950 nm and a half‐peak width of 162 nm. It is worth noting that with the same actual Cr 3+ content, the luminous intensity of Cs 2 NaScCl 6 synthesized by the improved solid‐phase synthesis is four times higher than the product synthesized by the hydrothermal method. an efficient Cl − ‐Cr 3+ charge transfer sensitization facilitated by localized electrons in [CrCl 6 ] 3− octahedron is the mechanism for the strong NIR emission of Cr 3+ is proposed. Calculations based on density functional theory and Bader charge analysis support the notion that electrons in [CrCl 6 ] 3− octahedrons are strongly localized in Cs 2 NaScCl 6 :Cr 3+ , which is conducive to the Cl − –Cr 3+ charge transfer process, resulting the internal quantum efficiency of 100% and external quantum yield as 42.3%. The highly efficient ultra‐broadband NIR emission with excellent stability offers many opportunities for applications in the field of NIR night vision and bio‐imaging.