Novel Lead‐Free Stable Fluorite Nanocrystals and Their Applications in Light‐Emitting Diodes

Abstract The toxicity and the poor thermal stability of all‐inorganic lead perovskite nanocrystals (NCs) have been the major limitation for their scale‐up purpose. In this study, a novel lead‐free KEu 4 F 13 NCs are synthesized for the first time using a facile and eco‐friendly hydrothermal strategy. High‐resolution synchrotron X‐ray diffraction study indicates that KEu 4 F 13 NCs adopt a cubic fluorite structure with excess fluorine intercalated into the spare rooms of lattice. The obtained KEu 4 F 13 NCs have characteristic emission peaks of Eu 3+ ions excited by the wavelength of 394 nm. More importantly, the KEu 4 F 13 NCs show excellent thermal stability due to the small radius of F − ions and its high lattice energy. The relative photoluminescence (PL) intensity at 594 nm retains ≈72% of its initial value 20 °C when heated to 200 °C. Furthermore, the PL intensity shows negligible degradation after undergoing three consecutive thermal cycles between 20 and 200 °C. The X‐ray diffraction (XRD) peaks of KEu 4 F 13 NCs at 20 °C remain identical to those of the cycled samples (after 1st/3rd thermal cycles), confirming their structural robustness under thermal stress. The lifetimes of KEu 4 F 13 NCs measured at 20 and 180 °C are calculated to be 2.10 and 2.04 ms, respectively. The red‐emitting KEu 4 F 13 NCs are encapsulated on an ultraviolet (UV)‐emitting chip to fabricate red light‐emitting diodes (LED).