Enhanced Photoluminescence in Nitrogen–Boron-Codoped Carbon Dots: A First-Principles Study on Synergistic Charge Transfer Mechanisms

Abstract

The low photoluminescence (PL) quantum yield of carbon dots (CDs) has constrained their practical implementation in commercial applications. The inherent limitations of conventional single-element doping prevent it from overcoming this key performance bottleneck and achieving a synergistic enhancement. In this study, the fluorescence properties of nitrogen–boron (N,B)-codoped CDs were systematically investigated using first-principles calculations. N dopants tend to coexist with surface BC3-configured boron atoms, and the pyridinic N–B-codoped configuration is effective in enhancing the thermodynamic stability of CDs. Cooperative interactions between the low-electronegativity B and varied N heteroatoms facilitate synergistic intramolecular charge transfer across the carbon domain. Enhanced charge delocalization reshapes the excited-state transition from a multiorbital mixture to one dominated by the HOMO–LUMO channel. Hence, all N-BC3-codoped configurations exhibit enhanced fluorescence intensity, with pyrrolic N–B codoping being particularly effective. This mechanism underlies the universally observed emission redshift and significant fluorescence enhancement in N-BC3 configurations, while also explaining why analogous enhancements are rarely seen in the more common N-BC2O and N-BCO2 configurations. These findings offer valuable insights for the rational design of dual-doped CDs for advanced optoelectronic and biomedical applications.