Electrochemical exfoliation of phosphorus doped carbon dots with dual-emission originating from carbon core and surface states

Carbon dots have attracted significant attention due to their versatile and excellent photoelectric properties; however, the origins and underlying mechanism remain a subject of debate especially for dual-emission CDs. Here, novel dual-emission CDs have been exfoliated from graphite rods via an electrochemical method in a dihydrogen phosphate electrolyte. The CDs possess a very narrow blue emission band in the short wavelength region and a broad cyan emission band in the long wavelength range, which are attributed to carbon core state and surface state from phosphorus atom doping, respectively. Interestingly, the former shows excitation-dependent behavior, but the latter is excitation-independent. Thus, as the excitation wavelength increases, the blue emission band is gradually closing to the cyan one and coalesce into a broad peak at the excitation wavelength of 420 nm. The variations of both emission intuitively illustrate the role transition between a core state and the doped surface state at different excitation wavelengths, which offer a real sample for the study of transition between emissive states. Our findings provide novel and fundamental insights on the fluorescence mechanism of CDs with dual-emission.