First principles investigation of electronic and optoelectronic properties of N and O codoped carbon quantum dots

Carbon Quantum Dots (CQDs) have emerged as a prominent class of carbon-based nanomaterials for optoelectronic applications. In this work, the electronic structure of N, O co-doped CQDs with a carboxylic acid functional group was extensively studied via First-Principles density functional theory computations performed at the B97-3c/def2-mTZVP level. Geometry optimization showed that the structure was effectively relaxed, with convergence attained after 44 iterations. The frontier molecular orbitals analysis indicated a reduced electronic gap of 1.47 eV, which suggests narrow-gap semiconductor characteristics arising from the cooperative N, O co-doping effects. Electrostatic potential mapping as well as the Mulliken charge population analysis revealed significant polarization and rearrangement of the charges, allowing for effective intramolecular charge transfer and exciton dissociation. Vibrational spectroscopy and nuclear magnetic resonance data confirmed the doping effects of the heteroatoms and associated changes in the local environment. These findings reveal improved charge separation and a reduced electronic gap, confirming enhanced surface chemistry. As such, the N, O co-doped CQDs are ideal for applications in light-emitting diodes, photo detectors, photocatalysis, and sensing. These insights provide valuable structure–property relationships and design guidelines for engineering next-generation carbon-based quantum dots for high-performance optoelectronics.