Color-Tunable Carbon Dots with Aggregation-Induced Emission Constructed by FRET between Surface Luminescence Centers

As a class of new fluorescent materials, carbon dots (CDs) have drawn widespread attention by virtue of their tunable photoluminescence (PL), excellent biocompatibility, and novel physicochemical properties. Unfortunately, in solid state, most CDs experience serious aggregation-caused quenching (ACQ). In this work, color-tunable CDs with aggregation-induced emission (AIE) are prepared by simply changing the filling ratio of the autoclave. The obtained CDs show dual emission (green/red) in solid state, and the fluorescent color can be tuned from green to red. These CDs all exhibit blue fluorescence in dilute solution, and aggregation-induced redshift behaviors are observed when the CDs form aggregates. Structural and optical characterizations prove that blue fluorescence is contributed by the carbon cores, whereas the green/red emission is attributed to the surface groups. Multicolor fluorescence is caused by increased fluorescence resonance energy transfer (FRET) efficiency among the dual emission (green/red) peaks from g-CDs to r-CDs. Surprisingly, delayed fluorescence (DF) of CDs are brightened by inserting the CDs into poly(vinyl alcohol) (PVA) films, which can be easily recognized by the naked eyes with a lifetime up to ms. Finally, owing to the unique AIE and DF properties, the four CDs can be applied to multimodal advanced anti-counterfeiting and information encryption.