Role of Intrinsic Atomic Features and Bonding Motifs from the Surface to the Deep Core on Multistate Emissive Properties of N,B-Codoped Carbon Dots

Controlling the fundamental photophysical properties of the heteroatom-doped luminescent carbon dots (CDs) has become a challenge due to the lack of fundamental understanding of the correlation between structural and optical properties. Here, we have synthesized green emissive nitrogen (N) doped and intense blue emissive nitrogen, boron (N,B) codoped carbon dots by a typical one-step microwave irradiation technique. To unveil the correlation between their intricate structural features and tunable emissive properties, we have carried out steady-state and time-resolved optical spectroscopy experiments, as well as X-ray photoelectron spectroscopy (XPS) and synchrotron near K-edge X-ray absorption fine structure (NEXAFS) measurements. We have observed the formation of a specific green emissive molecular domain on the surface of N-doped carbon dots which is almost absent in the NB-codoped sample. Although the core domains of both systems remain aromatic, their intrinsic atomic compositions and electronic structure were found to be different. Consequently, the simultaneous coexistence of B with N influences the electron delocalization and energy-level alignments, which eventually alter the overall photophysics of the codoped CDs.