In this study, lead-free cesium tin halide (Cs 2 SnBr 6 ) double-perovskite nanocrystals (DPNCs) were synthesized and investigated using an easy hot-injection method. Hexagonal-shaped Cs 2 SnBr 6 DPNCs, having cubic symmetry with the Fm3̅ m space group, were exhibited for the first time through X-ray diffraction and Raman experiments. The bandgap structures and photoluminescence (PL) mechanism of self-trapped excitons in the Cs 2 SnBr 6 DPNCs were experimentally demonstrated by X-ray photoelectron and ultraviolet (UV)−visible absorption spectroscopy. The prepared Cs 2 SnBr 6 DPNCs had an average size of approximately 58 nm and generated orange emission at a wavelength of 600 nm (full-width at halfmaximum, 121 nm). These samples exhibited a PL quantum yield of approximately 31% and fluorescence lifetime of approximately 3.3 μs. The Cs 2 SnBr 6 DPNCs and blue phosphor (Sr 5 (PO 4 ) 3 Cl:Eu 2+ ) were mixed with polydimethylsiloxane packaging in 365 nm UV lightemitting diodes (LEDs), which were used to fabricate candlelight LEDs with a color-rendering index of 84 and a correlated color temperature of 2006 K. All these results can significantly contribute to the global use of low-toxicity and environmentally friendly luminescent materials for lighting sources.

In this study, for the first time, we propose CSP QD-LEDs with excellent stability, high color uniformity, and wide color gamut for backlight displays.