Linear and Nonlinear Optical Properties of Graphene Quantum Dots: A Computational Study

Abstract

Because of the advantages of tunability via size, shape, doping, and relatively low level of loss and high extent of spatial confinement, graphene quantum dots (GQDs) are emerging as an effective way to control light by molecular, engineering. The collective excitation in GQDs shows high energy plasmon frequency along with frequencies in the terahertz (THz) region, making these systems powerful materials, for photonic technologies. Here, we report a systematic study of the linear and nonlinear optical properties of large varieties of GQDs (similar to 400 systems) in size and topology utilizing the strengths of both semiempirical and first-principle methods. Our detailed study shows how the spectral Shift and trends in the optical nonlinearity of GQDs depend on their structure, size, and shape. Among the circular, triangular, stripe, and random shaped GQDs, we find that GQDs with inequivalent sublattice atoms always possess lower HOMO-LUMO gap, broadband absorption, and high nonlinear optical coefficients. Also, we find that a majority of the GQDs with interesting linear and nonlinear optical properties have zigzag edges, although the revere is not always true. We strongly believe that our findings can act as guidelines to design GQDs in optical parametric oscillators, higher harmonic generators, and optical modulators.