Photoluminescent\nMulticolor Carbon Dots for UV Detection\nand Dynamic Anticounterfeiting

Carbon dots (CDs) are an emerging type of fluorescent\ncarbon nanomaterial\nwith broad application prospects. Among them, photochromic CDs have\nbeen widely used in the field of optoelectronic devices but rarely\nin ultraviolet (UV) detection. In this work, we successfully developed\nphotochromic CDs that exhibit reversible emission under light stimulation\nin an amine solvent system. Notably, the CDs showed ultrafast photochromic\nbehavior in diethylamine solvent, shifting the fluorescence color\nfrom cyan-green to orange-red after 2 s of irradiation, with the solution\ncolor changing from pale yellow to pale purple. Furthermore, this\nperformance could recover without additional stimuli, simply by standing\nfor several tens of seconds. Structural analysis indicated that rapid\nphotochromism arises from changes in the surface functional group\nradicals of the CDs, with the reversibility attributed to fluctuation\nin these radicals. Leveraging the excellent photochromic properties\nof CDs, we further developed a device for detecting UV indices in\nsunlight. This opens up broad prospects for developing high-performance\nUV detection devices based on CDs.