Theoretical investigation of electronic and optical properties of nitrogen doped triangular shaped graphene quantum dots

The electronic and optical properties of graphene quantum dots can be significantly tailored by doping it with heteroatoms, thus extending its potential applications. In this work, we have employed time-dependent density functional theory to systematically explore the effect of introduction of nitrogen atoms in varying concentration at pyridinic and graphitic configuration in armchair and zigzag-edged triangular shaped graphene quantum dots (TQDs) of different sizes. Our results indicate that the electronic band-gap in these N-doped systems can be effectively tuned by varying the configuration as well as concentration of dopants and nature of edge-termination. The variation of electronic band-gap is critically determined by the localized/delocalized nature of molecular orbitals and presence of additional energy levels due to dopant nitrogen atoms. However, the significance of these extra energy levels in modulating the optical properties (appearance of characteristic N-dopant absorption peaks) becomes conspicuous only for specific configuration and concentration of nitrogen atoms. In addition, our studies have attributed the strong dependence of blue/red-shift of absorption spectra and variation in the peak profile to position as well as concentration of dopant atoms and edge-termination pattern. Further, it is observed that the effect of increasing size of TQDs on the strength of most intense absorption peak of pyridinic N-doped TQDs is remarkably different from graphitic N-doped systems. This selective manipulation of optical properties in TQDs due to different N-doping pattern can open up new frontiers for rational design of novel optoelectronic devices.