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

Abstract Lanthanide‐based lead‐free perovskite materials hold great promise for the development of high‐resolution full‐color displays in the future. Here, various Cs 3 LnCl 6 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 Cs 3 EuCl 6 NCs as an intermediate state, Cs 3 EuCl 6 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 Cs 3 EuCl 6 ‐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.