Theoretical insights into tunable optical and electronic properties of graphene quantum dots through phosphorization

Abstract

Doping heteroatoms or covalent bonding with specific groups is an effective route to modify optical and electronic properties of graphene quantum dots (GQDs). In this work, effects of five phosphorous (P) bonding configurations (i.e., C2P, C2PO, C2PO2, C3P, and C3PO) on optical and electronic properties of GQDs are investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Optical absorption spectra, HOMO–LUMO gaps, and excited states of GQDs doped with different P bonding configurations at various locations are calculated to reveal electron transition processes. Due to the availability of vacant third orbitals, Ρ can have various stereochemistry and bonding. It is demonstrated that P bonding configurations with different geometrical configurations have various influences on the spectra of doped GQDs, and the existence of PO double bond in C2PO2 and C3PO configurations can induce multiple absorption peaks in P-doped GQDs. The calculated HOMO–LUMO gap has a larger gap reduction when P exhibits the sp3 hybridization. According to excited state analysis, P-doping with tetrahedral-like configurations has more evident effect on electronic structure of P-doped GQDs, while pyramidal-like configurations have noticeable charge transfer ability in the absorption process.