Synthesis and luminescence mechanism of fluorine-doped carbon dot-based composites with long lifetime and dual-mode afterglow

Abstract

Carbon dots (CDs) as afterglow materials have advantages including easily available raw materials, cost effectiveness, low toxicity, facile surface functionalization, and tunable spectra, demonstrating potential applications in anti-counterfeiting, information encryption, optoelectronics, sensing, and bioimaging. However, most current CD-based afterglow materials exhibit either room-temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF) emission, with few demonstrating both properties simultaneously. Their short afterglow lifetimes further limit practical applications. Herein, a long-lifetime dual-mode afterglow F, N-CDs@BA composites were prepared by fluorine doping strategy using boron oxide (B₂O₃) as the matrix. The TADF emission wavelength of F, N-CDs@BA is 430 nm, the lifetime is 1.21 s, and the afterglow is visible to the naked eye for about 11 s. The RTP emission wavelength is 510 nm, the lifetime is 0.47 s, and the afterglow is visible to the naked eye for about 13 s. Structural and optical characterizations revealed that the afterglow sources of F, N-CDs@BA composites at 430 and 510 nm originate from F, N-CDs and B₂O₃ matrices, respectively. Comparative analysis of structural and optical properties, combined with density functional theory calculations of electronic bandgap changes, confirmed that fluorine incorporation reduces the band gap and prolong the afterglow lifetime. All F, N-CDs embedded in different matrices exhibit afterglow emission, demonstrating their matrix universality. Finally, F, N-CDs@BA composites show potential application value in graphic anti-counterfeiting.