Photoluminescent Multicolor Carbon Dots for UV Detection and Dynamic Anticounterfeiting.

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