Synthesis of fluorescent polymeric carbon nitride quantum dots in molten salts for security inks

Abstract

Polymeric carbon nitride quantum dots (CNQDs) with an average size of approximately 2.5 nm were prepared directly from melamine via a one-step molten salt method. The formation mechanism and photoluminescence (PL) properties of the resulting CNQDs were investigated by means of TEM, XRD and PL spectroscopy. The CNQDs can be dispersed in water to form a transparent colloidal solution and emit blue PL with excellent photostability. Interestingly, upon addition of CuCl₂ and NaHCO₃ in turn, the PL of CNQDs can be turned off and on accordingly. Taking advantage of the on–off–on PL response, the CNQDs can be used as a fluorescent security ink for information coding, encryption and decryption, indicating their promising application in data security and high-level anti-counterfeiting fields.