Unveiling Local Electronic Structure of Lanthanide-Doped Cs NaInCl Double Perovskites for Realizing Efficient Near-Infrared Luminescence.

Lanthanide ion (Ln )-doped halide double perovskites (DPs) have evoked tremendous interest due to their unique optical properties. However, Ln ions in these DPs still suffer from weak emissions due to their parity-forbidden 4f-4f electronic transitions. Herein, the local electronic structure of Ln -doped Cs NaInCl DPs is unveiled. Benefiting from the localized electrons of [YbCl ] octahedron in Cs NaInCl DPs, an efficient strategy of Cl -Yb charge transfer sensitization is proposed to obtain intense near-infrared (NIR) luminescence of Ln . NIR photoluminescence (PL) quantum yield (QY) up to 39.4% of Yb in Cs NaInCl is achieved, which is more than three orders of magnitude higher than that (0.1%) in the well-established Cs AgInCl via conventional self-trapped excitons sensitization. Density functional theory calculation and Bader charge analysis indicate that the [YbCl ] octahedron is strongly localized in Cs NaInCl :Yb , which facilitates the Cl -Yb charge transfer process. The Cl -Yb charge transfer sensitization mechanism in Cs NaInCl :Yb is further verified by temperature-dependent steady-state and transient PL spectra. Furthermore, efficient NIR emission of Er with the NIR PLQY of 7.9% via the Cl -Yb charge transfer sensitization is realized. These findings provide fundamental insights into the optical manipulation of Ln -doped halide DPs, thus laying a foundation for the future design of efficient NIR-emitting DPs.