Synthesis of multicolor fluorescent CDs from natural plant kaempferide and their application in anti-counterfeiting inks

Carbon dots (CDs) are versatile nanomaterials with tunable luminescent properties. We used a natural plant kaempferol as a carbon source to synthesize multicolor CDs by reacting it with various nitrogen sources. Blue, green, and red CDs (B-CDs, G-CDs, and R-CDs) with emission wavelengths of 445 nm, 510 nm, and 600 nm respectively were successfully synthesized. Their photoluminescence quantum yields of are up to 37.4%, 20.1%, and 30.8%, respectively. Surface analysis revealed abundant nitrogen groups influencing luminescence. B-CDs and G-CDs show excitation-dependent emissions, indicating a potential correlation between their luminescence and particle sizes, while R-CDs exhibit excitation-independent emission, suggesting they belong to molecular state CDs. All three CDs exhibit stable luminescent performance, as well as good salt resistance and photobleaching resistance. The practical application of multicolored CDs in anti-counterfeiting fluorescent inks was further explored. This work offers a straightforward, eco-friendly route to synthesize multicolor CDs.