Pressure-Induced Bifurcation in the Photoluminescence of Red Carbon Quantum Dots: Coexistence of Emissions from Surface Groups and Nitrogen-Doped Cores.

Carbon quantum dots (CDs) with favorable fluorescent properties have stimulated considerable effort to modulate their photoluminescence (PL) for bioimaging and sensing. However, the fluorescent mechanisms are still only partially understood due to the diverse physicochemical properties of CDs prepared by various synthesis methods and postpreparation processes. In this report, pressure-induced bifurcation of PL is reported in red carbon quantum dots (R-CDs) for the first time. The splitting of PL into an irreversible blue-shifted peak and a reversible red-shifted peak under pressure suggests the coexistence of multiple fluorescent mechanisms in R-CDs, i.e., emissions from surface groups and nitrogen-doped cores. The concentration and excitation laser energy dependencies of pressure-induced bifurcation, as well as the time-resolved PL, further support the coexistence of multiple emitters. Our results provide a method for distinguishing between the different fluorescent mechanisms related to surface groups and carbon cores in CDs.