Visible-Light-Excited Room-Temperature Phosphorescent Carbon Dots via Surface Amination in a Microreactor for Multimode Anticounterfeiting

Carbon dots (CDs) with a long-lifetime room-temperature phosphorescence (RTP) have received considerable attention but still remain a great challenge, especially for synthesizing visible-light-excited RTP CDs. Until now, most studies have applied isolated and chromophorous reactants to achieve visible-light-excited RTP CDs. Therefore, those strategies to modulate the excitation wavelength are not referential or reproducible. Herein, surface amination and combination with boric acid (BA, H3BO3) of CDs are applied to build long-lifetime RTP, which drives excitation light from the ultraviolet (UV) area to the visible area and gives out excitation-related afterglow. Meanwhile, surface amination promotes the intersystem crossing process, increasing the quantum yield to 18.63%. After removal of excitation light, the afterglow time visible to naked eyes can reach 10 s, with a phosphorescence lifetime of 453 ms. Furthermore, time-dependent density functional theory (TDDFT) explained the differentiated influence of surface amination on the triplet state and singlet state, which benefits the idea of realizing a wider region for excitation. Based on the above features, CDs@BA are applied in encryption with different excitation wavelengths in the advanced anticounterfeiting security field.