Efficient and Stable Multicolor Emissions of the Coumarin‐Modified Cs3LnCl6 Lead‐Free Perovskite Nanocrystals and LED Application

Lanthanide-based lead-free perovskite materials hold great promise for the development of high-resolution full-color displays in the future. Here, various Cs₃LnCl₆ perovskite nanocrystals (NCs) emitting light across the visible to near-infrared spectrum with remarkably high photoluminescence quantum yield (PLQY) are systemically prepared. Especially, by introducing multifunctional coumarin small molecules into Cs₃EuCl₆ NCs as an intermediate state, Cs₃EuCl₆ NCs can achieve an impressive PLQY of 92.4% with pure red emission and an exceptional energy transfer efficiency of nearly 93.2%. Furthermore, the lanthanide-based electroluminescent devices in red, green, and blue are successfully fabricated. Among them, the Cs₃EuCl₆-NC-based red light-emitting diode (LED) demonstrates a FWHM of 18 nm at 617 nm, an external quantum efficiency up to 5.17%, and a maximum brightness of 2373 cd m^-2, which is the most excellent reported for lead-free narrowband (within 20 nm) emission devices. Notably, these devices exhibit an operating half-life of 440 h at a brightness level of 100 cd m^-2, surpassing the performance of most reported lead-free perovskite LEDs (PLEDs). This work opens up exciting possibilities for the future commercialization of lanthanide-based PLEDs in the display industry, paving the way for more vibrant, energy-efficient, and long-lasting display technologies.