3d Transition metal and nitrogen co-doped graphene: first-principles study of electronic structure and optical properties

Abstract

Engineering the optical properties of graphene through strategic doping is crucial for advancing optoelectronic applications. In this study, we systematically investigate the electronic structure and optical properties of nitrogen and 3d transition metal (Ti–Cu) co-doped graphene (TMNG) using density functional theory. Our calculations reveal that magnetic transition metals (Mn, Fe, Co, Ni) induce significantly enhanced light absorption in the near-infrared region, with Co–N co-doping exhibiting the strongest optical response and a magnetic band gap of 0.369 eV. Non-magnetic elements (Ti, V, Cr, Cu) show monotonically increasing regulatory effects with atomic number. By modulating nitrogen concentration in the Co–N system (CoN_xG, x = 1–4), we achieve tunable absorption from near-infrared to visible regions, with absorption intensity increasing by up to 40% at higher N concentrations. Phonon dispersion analysis confirms structural stability, while charge density and density of states calculations elucidate the underlying mechanisms of TM-d and C/N-p orbital hybridization. This work establishes design principles for graphene-based photodetectors with tailored spectral responses, highlighting the pivotal role of 3d transition metals in regulating photoresponse.