An Ultrafast and Room‐Temperature Strategy for Kilogram‐Scale Synthesis of Sub‐5 nm Eu³⁺‐doped CaMO₄ Nanocrystals with a Photoluminescence Quantum Yield Exceeding 85%

Abstract Rare earth‐doped metal oxide nanocrystals have a high potential in display, lighting, and bio‐imaging, owing to their excellent emission efficiency, superior chemical, and thermal stability. However, the photoluminescence quantum yields (PLQYs) of rare earth‐doped metal oxide nanocrystals have been reported to be much lower than those of the corresponding bulk phosphors, group II‐VI, and halide‐based perovskite quantum dots because of their poor crystallinity and high‐concentration surface defects. Here, an ultrafast and room‐temperature strategy for the kilogram‐scale synthesis of sub‐5 nm Eu³⁺‐doped CaMoO₄ nanocrystals is presented, and this reaction can be finished in 1 min under ambient conditions. The absolute PLQYs for sub‐5 nm Eu³⁺‐doped CaMoO₄ nanocrystals can reach over 85%, which are comparable to those of the corresponding bulk phosphors prepared by the high‐temperature solid state reaction. Moreover, the as‐produced nanocrystals exhibit a superior thermal stability and their emission intensity unexpectedly increases after sintering at 600 °C for 2 h in air. 1.9 kg of Eu³⁺‐doped CaMoO₄ nanocrystals with a PLQY of 85.1% can be obtained in single reaction.