Electrochemical synthesis of fluorescence-enhanced carbon dots with multicolor emission via surface nitrogen and sulfur modulation for information encryption applications

Multicolor emissive carbon dots (CDs) hold great potential for a wide range of applications in various fields. However, the luminescence enhancement mechanism is still controversial due to combined effects of the carbon core and surface states. Herein, we elucidate the surface state mechanism for the tunable and enhanced photoluminescence of CDs via only surface nitrogen and sulfur modification (N,S-CDs) through an electrochemical synthesis method. It is demonstrated that surface nitrogen functionalization with increasing content of NH2 groups leads to multicolor emission from blue to red. Moreover, surface sulfur functionalization with the introduction of C-S bonds can further improve the luminescence intensity by facilitating the transition of S-related excitation electrons and radiative recombination. In addition, the high luminance of N,S-GCDs enables their application in flexible fluorescence films, latent fingerprint detection and information encryption.