Carbon dots (CDs) are a kind of zero-dimensional carbonaceous nanomaterial. Due to their ultra-small size (usually less than 10 nm), simple synthesis, low toxicity, well-documented biocompatibility, and outstanding luminescent properties, CDs have wide applications, particularly in bioimaging and biomedical fields. Until now, efficient blue and green emissions with photoluminescence quantum yield (PLQY) higher than 60% have been reported in several CDs systems, while efficient pure red emissive CDs are still scarce. Noninvasive in vivo fluorescence (FL) imaging calls for an ideal working spectral window in red to NIR range of 650‒1450 nm. Therefore, CDs with strong emissions in red to NIR region in aqueous solutions are highly desired.