Efficient Deep-Blue Light-Emitting Diodes from Highly Luminescent Eu²⁺-Doped Alkali Metal Halide Nanocrystals via...

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 (Eu²⁺)-doped alkali-metal halides (AX:Eu²⁺; A = Na⁺, K⁺, Rb⁺, Cs⁺; X = Cl^-, Br^-, I^-) NCs is reported. Through adjustment of the coordination environment, efficient deep-blue emission from Eu-5d → Eu-4f transitions is realized. The representative CsBr:Eu²⁺ 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:Eu²⁺ 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 cm² are realized with uniform emission, representing a milestone toward commercial display applications.