Regulation mechanisms of tea residue-based carbon dots in water-induced full-color emission and applications of visual ratio water sensors in organic solvents and WLEDs.

The development and synthesis of near-infrared (NIR) and multicolor fluorescent biomass-derived carbon dots (CDs) have always been a hot topic and challenge in research. Here, NIR-emitting R-CDs are synthesized by a facile one-pot solvothermal method with tea leaf residues as carbon sources and gram-scale production is achieved. The results demonstrated that R-CDs in organic solvent systems show high sensitivity to water due to the carbon core-state emission quenching by the hydrogen bonding and the excited-state intramolecular proton transfer effects and the transition of surface groups governing the dominant fluorescence emission, and exhibit tunable multi-peak emission and full-color luminescence with water content. The visual ratio fluorescence water sensors in volatile organic compounds (including DMF, acetonitrile, ethanol and acetone) are prepared, and low detection limits (0.103 % for N, N-dimethylformamide, 0.068 % for ethanol) are obtained over a wide linear range (0-100 %) with good generalization to various organic solvent systems. The sensor is further utilized to detect different kinds of commercial wines and alcohols, revealing a relatively low standard deviation (≤0.61 %), substantiating its accuracy, practicality, and reliability in real-world applications. This dual-sensing strategy employing fluorescence quenching and emission peak blue-shift presents a novel direction for the development and design of sensors. Additionally, R-CDs-based WLEDs are successfully constructed by utilizing the unique luminescent property to achieve high-performance white light emission. This provides technical ideas for the facile and visualized detection of water content in organic solvents and the development of CDs-based WLEDs.