Spectra stable deep-blue light-emitting diodes based on cryolite-like cerium(III) halides with nanosecond d-f emission.

Next-generation wide color gamut displays require the development of efficient and toxic-free light-emitting materials meeting the crucial Rec. 2020 standard. With the rapid progress of green and red perovskite light-emitting diodes (PeLEDs), blue PeLEDs remain a central challenge because of the undesirable color coordinates and poor spectra stability. Here, we report CsCeBrI ( = 0 to 6) with the cryolite-like structure and stable and tunable color coordinates from (0.17, 0.02) to (0.15, 0.04). Further encouraged by the short exciton lifetime (26.1 ns) and high photoluminescence quantum yield (~76%), we construct CsCeBrI-based rare-earth LEDs via thermal evaporation. A seed layer strategy is conducted to improve the device's performance. The optimal CsCeI device achieves a maximum external quantum efficiency of 3.5% and a luminance of 470 cd m with stable deep-blue color coordinates of (0.15, 0.04). Our work opens another avenue to achieving efficient and spectrally stable deep-blue LEDs.