Modulation of red-light emission from carbon quantum dots in acid-based environment and the detection of chromium (Ⅲ) ions

In this study, the carbon quantum dots, which can emit sharp red light (R-CQDs) under optical excitation, were synthesized via simple heat treatment of wine lees. The features of the photoluminescence (PL) emission from R-CQDs in solutions with different pH values and with metal ions were examined. The intensity of the PL emission from R-CQDs depends sensitively on the pH values of the solutions with the R-CQDs. Interestingly, the pH-response of the PL intensity is reversible and can be enhanced linearly in the pH value range from 4 to 12, indicating that the R-CQDs can be applied for the pH sensor. Furthermore, the quench of the PL emission from R-CQDs can be observed when adding chromium (III) ions into the solution with R-CQDs. This effect can be utilized for selective and quick detection of chromium (III) ions in solutions simply via the standard PL measurement. The interesting and important findings from this work can be applied to explore more practical applications of the CQDs prepared cheaply and easily.