Tunable and Efficient Photoluminescence of Lanthanide-Doped Cs2NaScCl6 Double Perovskite Single Crystals toward Multifunctional Light-Emitting Diode Applications

Lead-free halide double perovskite, as one of the promising candidates for lead halide perovskite materials, shows great potential in light-emitting diodes (LEDs), benefiting from its environmental friendliness and high chemical stability. However, the poor regulation of the emission spectra severely limits its application range. Herein, various lanthanide ions were successfully doped in Cs₂NaScCl₆ double perovskite single crystals (DPSCs) to yield effective and stable emissions spanning from visible to near-infrared (NIR) regions. Notably, efficient energy transfer from the host to the dopants enables tunable emissions with good chromaticity, which is rarely reported in the field of lead-free double perovskite. Moreover, density functional theory calculations reveal that the high local electron density around the [LnCl₆]^3- octahedron in DPSCs plays a key role in the improvement of photoluminescence quantum yields (PLQYs). The optimal PLQYs are up to 84%, which increases around 3 times over that of the undoped sample. Finally, multicolor and NIR LEDs based on Ln³⁺-doped Cs₂NaScCl₆ DPSCs were fabricated and had different application functions. Specifically, the single-composite white LED shows adjustable coordinates and correlated color temperatures, while the NIR LED shows good night vision imaging. This work provides new inspiration for the application of efficient multifunctional LEDs based on lead-free double perovskite materials.