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

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.