Efficient Deep-Blue Light-Emitting Diodes from Highly Luminescent Eu-Doped Alkali Metal Halide Nanocrystals via Lattice Field Modulation.

Lead-halide perovskite nanocrystals (NCs) are promising for fabricating deep-blue (<460 nm) light-emitting diodes (LEDs), but their development is plagued by low electroluminescent performance and lead toxicity. Herein, the synthesis of 12 kinds of highly luminescent and eco-friendly deep-blue europium (Eu)-doped alkali-metal halides (AX:Eu; A = Na, K, Rb, Cs; X = Cl, Br, I) NCs is reported. Through adjustment of the coordination environment, efficient deep-blue emission from Eu-5 → Eu-4 transitions is realized. The representative CsBr:Eu NCs exhibit a high photoluminescence quantum yield of 91.1% at 441 nm with a color coordinate at (0.158, 0.023) matching with the Rec. 2020 blue specification. Electrically driven deep-blue LEDs from CsBr:Eu NCs are demonstrated, achieving a record external quantum efficiency of 3.15% and half-lifetime of ∼1 h, surpassing the reported metal-halide deep-blue NCs-based LEDs. Importantly, large-area LEDs with an emitting area of 12.25 cm are realized with uniform emission, representing a milestone toward commercial display applications.