Common Origin of Green Luminescence in Carbon Nanodots and Graphene Quantum Dots

TLDR

Green‑fluorescent carbon nanomaterials such as C‑dots and GQDs are widely studied, yet the origin of their photoluminescence remains debated. The study aims to identify a common origin of green luminescence in C‑dots and GQDs. Ultrafast spectroscopy was employed to probe the emission centers in these nanomaterials. They found that green luminescence originates from edge states comprising carbon atoms and C=O functional groups, and that competition among these bright edge states and traps governs the optical behavior.

Abstract

Carbon nanodots (C-dots) synthesized by electrochemical ablation and small molecule carbonization, as well as graphene quantum dots (GQDs) fabricated by solvothermally cutting graphene oxide, are three kinds of typical green fluorescence carbon nanomaterials. Insight into the photoluminescence origin in these fluorescent carbon nanomaterials is one of the important matters of current debates. Here, a common origin of green luminescence in these C-dots and GQDs is unraveled by ultrafast spectroscopy. According to the change of surface functional groups during surface chemical reduction experiments, which are also accompanied by obvious emission-type transform, these common green luminescence emission centers that emerge in these C-dots and GQDs synthesized by bottom-up and top-down methods are unambiguously assigned to special edge states consisting of several carbon atoms on the edge of carbon backbone and functional groups with C═O (carbonyl and carboxyl groups). Our findings further suggest that the competition among various emission centers (bright edge states) and traps dominates the optical properties of these fluorescent carbon nanomaterials.