F and Na Co-doped carbon dots with enhanced afterglow emission for applications in fingerprint recognition and information encryption

Carbon dots (CDs) have attracted considerable interest as fluorescent nanomaterials; however, their long-afterglow emission properties remain underexplored. In this study, we synthesized dual-mode afterglow CDs exhibiting room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) via fluorine-sodium (F, Na) co-doping, achieving an extended afterglow lifetime of 574 ms. Under 365 nm UV excitation, the afterglow emission persists for 14 s (naked-eye observation) and 40 s (instrumentally quantified), demonstrating exceptional temporal resolution. Na doping enhances afterglow intensity by 11.3 %, while fluorine doping reduces the singlet-triplet energy gap (ΔE_ST) to 0.036 eV, facilitating efficient Reverse Intersystem Crossing and enabling TADF behavior. These synergistic effects position the developed CDs as promising candidates for anti-counterfeiting systems, multilevel data encryption, and high-security optical tagging.