Room-temperature phosphorescent fluorine-nitrogen co-doped carbon dots: Information encryption and anti-counterfeiting

The spin-forbidden nature of triplet exciton transitions is a limitation for achieving a carbon dots-based material with room-temperature phosphorescence (RTP). Here, fluorine-nitrogen co-doped carbon dots (FNCDs), prepared using the solvothermal method and further gas-phase fluorination from fructose and diethylenetriamine (DETA), were found to exhibit RTP lifetime and quantum yield of 1.14 s and 8.3%. By comparing the structure and performance of the nitrogen-doped carbon dots (NCDs) and FNCDs, it was found that the RTP of FNCDs originates from the π→π∗ and n→π∗ electron transitions C–N/CN, which can be attributed to the small energy gap between the singlet and triplet states. We further explored the mechanism of RTP by analyzing the hydrogen bonding between carbon dots and polyvinyl alcohol matrix. The semi-ionic C–F bonds also enhance intramolecular and intermolecular hydrogen bonding and reduce the quenching of RTP without the oxygen barrier. Furthermore, we applied the prepared aqueous FNCDs as an advanced security ink for information printing and anti-counterfeiting.