One‐Step Synthesis of Superbright Water‐Soluble Silicon Nanoparticles with Photoluminescence Quantum Yield Exceeding 80%

Fluorescent silicon nanoparticles (SiNPs) have shown potential applications in bioimaging/biolabelling, sensing, and nanomedicine/cancer therapy due to their superior properties such as excellent photostability, low cytotoxicity, and versatile surface modification capability. Here, a simple, high‐yield, and one‐pot method is developed to prepare superbright, water‐soluble, and amine‐functionalized SiNPs with photoluminescence quantum yield (PLQY) comparable to fluorescent II–VI semiconductor quantum dots (QDs) but with much lower cytotoxicity. By introducing a commercially available amine‐containing silane molecule, N‐[3‐(trimethoxysilyl)propyl]ethylenediamine (DAMO), water‐soluble SiNPs are prepared with PLQY of 82.4% via a microwave‐assisted method. To the best of our knowledge, this is the highest PLQY value ever reported for water‐soluble fluorescent SiNPs. The silicon element in our SiNPs is mainly four‐valent silicon and thus these SiNPs may also be termed as oxidized silicon nanospheres or silica nanodots. We have also demonstrated the importance of the silane structure (e.g., a suitable amine content) on the photoluminescence property of the prepared SiNPs. As revealed by the time‐resolved photoluminescence technique, the highest PLQY value of DAMO SiNPs is correlated with their monoexponential decay with a relatively long fluorescence lifetime. In addition, the potential use of these SiNPs has also been demonstrated for fluorescent patterning/printing and ion sensing (including Cu 2+ and Hg 2+ ).