Advanced dual-channel sensing of coumarin with phosphorescent carbon dots: Mechanism insights

Room-temperature phosphorescence carbon dots (CDs) show the highlighted advantages in chemical sensing and bioimaging owing to its long lifetime, however, acquiring the efficient phosphorescence of carbon dots is still encountering difficulty due to the spin prohibition. Here, we synthesized one type of CDs through one-step hydrothermal method. To be specific, the CDs displayed the blue fluorescence in aqueous, and emitted the bright green phosphorescence when being coated on the filter paper. Importantly, introducing coumarin to the CDs resulted in the distinct quenching of both its fluorescence and phosphorescence. Based on this phenomenon, we successfully established a dual-channel detection of coumarin. The fluorescence detection channel exhibited a linear range of 5–350 μM with a detection limit of 0.196 μM, while the phosphorescence detection channel achieved a linear range of 50–1000 μM with a detection limit of 0.268 μM. The further investigation revealed that IFE and SQE were mainly responsible for the fluorescence quenching of CDs, while the phosphorescence quenching was originated from the increased energy gap between the singlet and triplet states (ΔE ST ) of CDs, thus obstructing the ISC process. Moreover, we employed the CDs as the phosphorescent ink for anti-counterfeiting.