Dual-mode luminescence of rare‐earth ions doped halide perovskites for temperature sensing and anti-counterfeiting

Lead-free halide double perovskite up-conversion (UC) materials have attracted significant attention due to their unique photoelectric properties and eco-friendly features in the field of optoelectronics and energy research. However, their multimodal excitation mechanisms remain unclear, and research on these materials is still in early development. In this work, Er 3+ , Yb 3+ , Tb 3+ tri-doped lead-free halide double perovskite Cs 2 NaScCl 6 microcrystal (MCs) were synthesized via hydrothermal method. The crystal structure, morphology, and luminescent properties were investigated by X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy. The optical characterization reveals that Er 3+ /Yb 3+ /Tb 3+ co-doped Cs 2 NaScCl 6 MCs exhibit green luminescence by dual-mode excitation. When excited by 280 nm ultraviolet (UV) light, the 5 D 4 → 7 F 5 transition of Tb 3+ dominates the characteristic down-conversion (DC) emission at 546 nm. Under the 980 nm near-infrared (NIR) excitation, the MCs emit intense up-conversion (UC) emission of Er 3+ at 550 nm, generated by the 2 H 11/2  →  4 I 15/2 and 4 S 3/2  →  4 F 9/2 transition. By employing the luminescence intensity ratio between two thermally coupled energy levels of Er 3+ ( 2 H 11/2 and 4 S 3/2 ), a maximum relative sensitivity of 1.201% K −1 was achieved at 303 K. Furthermore, utilizing the green luminescence characteristics under 280 nm/980 nm dual-mode excitation, a digital encoding programming was developed to successfully demonstrate multilevel information encryption/decryption. All results indicate the Cs 2 NaScCl 6 : Er 3+ , Yb 3+ , Tb 3+ MCs have potential in various areas such as optical temperature sensing and anti-counterfeiting applications.