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Dramatic red fluorescence enhancement and emission red shift of carbon dots following Zn/ZnO decoration.

Metal atom doping, an easy and convenient method, can optimize and tune the physical-chemical properties and photometrics of carbon dots (CDs). However, there are few reports on the preparation of metal-decorated CDs that give red emission and a high photoluminescence quantum yield (PLQY). Here, we demonstrate a zinc (existing in human body) ion-doping strategy to observably enhance the PLQY and lengthen the CD emission wavelength. The prepared Zn/ZnO-decorated CDs (Zn-CDs) produced red fluorescence (623 nm) with a superior PLQY of 40.3%. Through a series of analyses, Zn-CDs were confirmed to contain an oxidation state and reduction state of Zn doping into the internal defects and surface of Zn-CDs. More valuably, the Zn-CDs had excellent chemical stability, photo-stability, long-term storage stability, and high biocompatibility, and therefore could be used as a robust red fluorescence probe for high-quality cellular imaging.