Tunable efficient visible and near-infrared multi-emission in Ho³⁺ doped Cs₂NaBiCl₆ double perovskite via Ag⁺ alloying

Herein, we successfully obtained Ho3+ and Ag+ -codoped Cs2NaBiCl6 halide double perovskites (DPs) via a hydrothermal method, which exhibit orange-red broadband self-trapped excitons (STE) emission and visible (Vis) and near-infrared (NIR) narrow band emission attributed to Ho3+ f-f transition, under 360 nm excitation. Compared to the single Ho3+-doped sample, the Vis PL intensity of the codoped sample was increased by nearly 13.8 times, and an enhanced photoluminescence quantum yield (PLQY) of 87.45 % was achieved. The PL enhancement is attributed to the partial substituting of Na+ with Ag+, leading to an efficient STE emission, and the more energy transition from STE to Ho3+. Moreover, the synthesized phosphor exhibits good stability in thermal and atmospheric environments. White light-emitting diode (WLED) is fabricated by employing Cs2Na0 & sdot;997Ag0 & sdot;003Bi0.935Ho0.065Cl6 on near-ultraviolet (n-UV) LED chips, achieving a color rendering index (CRI) of 95.0 and correlated color temperature (CCT) of 3814 K. Anti-counterfeit patterns and the application for night vision monitoring were also discussed. This study inspires the designing of high-quality phosphors of rare earthdoped DPs and expands the multi-domain luminescence applications of halide DPs.