Facile Melting-Crystallization Synthesis of Cs 2 Na x Ag 1- x InCl 6 : Bi Double Perovskites for White Light-Emitting Diodes.

Lead-free double perovskites (DPs) have outstanding luminescent properties, which make them excellent candidates for wide use in optoelectronics. Herein, a solvent-free melting-crystallization technique, which can produce kilogram-scale DP microcrystals (DP-MCs) in one batch, is invented to synthesize the Cs 2 Na x Ag 1- x InCl 6 : Bi ( x = 0, 0.2, 0.4, 0.6, 0.8, and 1) DP-MCs. The structure and composition analysis confirmed the products are pure Cs 2 Na x Ag 1- x InCl 6 DP-MCs. Affected by Jahn-Teller distortion of AgCl 6 octahedra, self-trapped excitons appear in the excited state, resulting in the broadband emission (400-850 nm) of Cs 2 Ag 1- x Na x InCl 6 : Bi DP-MCs. The enhancement of the photoluminescence quantum yield can be realized by introducing Na + to break the parity-forbidden transition in the Cs 2 AgInCl 6 DP. Optimized Cs 2 Na 0.4 Ag 0.6 InCl 6 : Bi DP-MC phosphors combined with commercial blue and green phosphors were coated on ultraviolet chips (365 nm) to fabricate white light-emitting diodes (WLEDs) from warm white (2930 K) to cold white (6957 K). An ultrahigh color rendering index of 97.1 and a CCT of 5548 K as well as Commission Internationale de l'Eclairage color coordinates of (0.331, 0.339) have been demonstrated. This kilogram-scale synthesis technique could stimulate the industrial development of WLEDs for general lighting based on DP-MC phosphors.