Blue Light-Excited Carbon Dot/C₃N₄ Nanocomposites with Long-Lived Thermally Activated Delay Fluorescence for Anti-Counterfeiting and Illumination

Long-lived thermally activated delayed fluorescence (TADF) emission has gained extensive attention due to its potential application in information encryption, illumination, and bioimaging. However, developing visible light-excited TADF materials is still a significant challenge. Herein, visible light triggered TADF emission was achieved by embedding chlorine doped carbon dots (Cl-CDs) into a g-C3N4 nanosheet matrix through a simple microwave treatment. The strong electron-withdrawing effect of the chlorine dropping redshifts the excitation wavelength, and the covalent bonds between Cl-CDs and the matrix significantly stabilize the triplet state. Green TADF with a peak at 520 nm could be obtained in the Cl-CD composite when excited by the UV to visible light, and the afterglow signal can be observed by the naked eye for up to 5 s after a mobile phone flashlight irradiation. The composite also exhibited temperature-responsive color stability under UV light irradiation. Consequently, the Cl-CD composite was successfully employed in concepts of information encryption and single-component time delay WLED development. This research provides materials and strategies that may motivate the visible light-excited TADF applied in advanced information encryption and illumination areas.