Carbon dot-based afterglow composite with tunable room temperature phosphorescence and thermally activated delayed fluorescence and their anti-counterfeiting and encryption application

Carbon dots (CDs) based afterglow materials have attracted much attention owing to their low toxicity, environmental protection, stable luminescence, abundant raw materials, and low cost. However, CD-based afterglow materials with both room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) characteristics are rarely reported, which greatly limits their in-depth application in advanced anti-counterfeiting, intelligent sensing, and other fields. In this paper, Cu, N co-doped CDs (Cu, N-CDs) with dual emission centers were synthesized via a simple solvothermal method by heteroatom doping to enhance the spin–orbit coupling of CDs and regulate the luminescence properties of CDs. Then, boric acid (BA) was used as the matrix to synthesize Cu, N-CDs@BA composites by matrix-assisted method, and the electron transfer enhancement afterglow was realized by the inorganic electronic defects of the matrix. Cu, N-CDs@BA can realize the mutual conversion of TADF and RTP by changing the excitation wavelength or increasing the temperature. At the excitation of 285 nm, the room temperature afterglow of Cu, N-CDs@BA exhibit TADF, and the average afterglow lifetime is 94.21 ms. At the excitation of 365 nm, they exhibit RTP, and the average afterglow lifetime is 347.96 ms. Based on three different emission properties (fluorescence, RTP, and TADF), Cu, N-CDs@BA was applied in anti-counterfeiting and encryption, which shows good application potential.