Facile Melting-Crystallization Synthesis of Cs₂Na_xAg_1-xInCl₆:BiDouble Perovskites for White Light-Emitting Diodes

Lead-free double perovskites (DPs) have out-standing luminescent properties, which make them excellentcandidates for wide use in optoelectronics. Herein, a solvent-freemelting-crystallization technique, which can produce kilogram-scale DP microcrystals (DP-MCs) in one batch, is invented tosynthesize the Cs2NaxAg1-xInCl6:Bi(x= 0, 0.2, 0.4, 0.6, 0.8, and1) DP-MCs. The structure and composition analysis confirmed theproducts are pure Cs2NaxAg1-xInCl6DP-MCs. Affected by Jahn-Teller distortion of AgCl6octahedra, self-trapped excitons appearin the excited state, resulting in the broadband emission (400-850nm) of Cs2Ag1-xNaxInCl6: Bi DP-MCs. The enhancement of thephotoluminescence quantum yield can be realized by introducing Na+to break the parity-forbidden transition in the Cs2AgInCl6DP.Optimized Cs2Na0.4Ag0.6InCl6: Bi DP-MC phosphors combined with commercial blue and green phosphors were coated onultraviolet chips (365 nm) to fabricate white light-emitting diodes (WLEDs) from warm white (2930 K) to cold white (6957 K). Anultrahigh color rendering index of 97.1 and a CCT of 5548 K as well as Commission Internationale de l'Eclairage color coordinatesof (0.331, 0.339) have been demonstrated. This kilogram-scale synthesis technique could stimulate the industrial development ofWLEDs for general lighting based on DP-MC phosphors.