An innovative and green strategy to synthesize carbon dots (CDs) with a quantum yield (QY) of nearly 19.8% has been successfully established for the first time. Subsequently, the possible fluorescence (FL) mechanism was elucidated by fluorescence, UV–vis, high resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. Significantly, not only the precursor of CDs and whole synthesis procedure was green, but also the CDs obtained here exhibited various advantages including high fluorescent QY, excellent photostability, non-toxicity and satisfactory stability. Additionally, the CDs were employed for assaying Fe3+ based on direct interactions between Fe3+ and COOH, OH and NH2 of CDs, resulting in aggregations that facilitate to quench their fluorescence. The decrease of fluorescence intensity permitted detections of Fe3+ in a linear range of 5.0×10−9–1.0×10−4mol/L, with a detection limit of 1.7×10−9mol/L at a signal-to-noise ratio of 3, suggesting a promising assay for Fe3+. Eventually, the CDs were applied for cell imaging and coding, demonstrating their potential towards diverse applications. •A green, novel, one-pot strategy for synthesizing carbon dots was established.•A simple, sensitive and cost-effective quantification of Fe3+ was developed.•The carbon dots could serve for fluorescent staining, coding and bioimaging.