External Electric Field Induced Second-Order Nonlinear Optical Effects in Hexagonal Graphene Quantum Dots

Abstract

The second-order nonlinear optical (NLO) effects are usually forbidden in materials with inversion symmetry, which restricts the application of graphene in NLO technologies such as phase-only modulation, second-harmonic generation, and sum/difference frequency generation. Here, we break the centrosymmetry by applying external uniform electrostatic fields across hexagonal graphene quantum dots (GQDs) and induce a second-order NLO response in the centrosymmetric GQDs. Ab initio quantum chemistry methods were performed to investigate the external electric field effects on the electronic structure and the electronic first hyperpolarizability of the hexagonal GQDs. Under the action of an external electric field, centrosymmetries of the geometric structure and electron density distribution of the hexagonal GQD are both broken, thereby resulting in nonzero electronic first hyperpolarizability. The external electric field induced electronic first hyperpolarizability shows remarkable anisotropy for different directional fields. Particularly, under the electric field of a certain direction, the field dependence of electronic first hyperpolarizability shows a nonmonotonic trend. The electron density redistribution induced by a strong electric field can significantly reduce the frontier orbital energy gap of the quantum dot, thereby evidently enhancing the electronic first hyperpolarizability. This study provides an important theoretical guidance for the experimental realization of an electrically tunable second-order NLO response in GQDs.

Electronic Structure Modulation of Nanographenes for Second Order Nonlinear Optical Molecular Materials

“…[9b,75] Moreover, applying external uniform electrostatic fields on NGs induces charge redistribution and changes the frontier MO energy, thus evidently affects the first hyperpolarizability. [76] Beside these strategies, fabrication of functionalized NGs through topologic defects or (and) heteroatoms doping has attracted increased attention because these modulations provide direct access to novel materials with intriguing optoelectronic properties while with minimal geometric deformation. [24] In the following sections, the abovementioned modulation strategies (i. e. topologic defects, heteroatoms doping, topologic defects combined with heteroatoms doping) to improve the NLO properties of NGs-based nanomaterials will be reviewed.…”

AlCl3-promoted growth of alkylated carbon dots with an enhanced nonlinear optical response

“…[1][2][3][4] Carbon nanomaterials, including fullerenes, carbon nanotubes (CNTs) and graphene/graphene oxide (GO), have the potential to obtain large nonlinearities and are being actively investigated on the realization of good NLO properties. [5][6][7][8] Being a class of photoluminescent (PL) carbon nanomaterials, carbon dots (CDs) have also shown promising potential to be used as NLO materials. 9,10 As CDs normally have small sizes (typically below 10 nm), nonlinear scattering, which is generally applied to explain the NLO response of the dispersions of CNTs and graphene/GO, can hardly work.…”

Nonlinear polarization effect of functionalized graphene quantum dots

“…Graphene quantum dots (GQD) represent one to several graphene layers with a size of less than 10 nm. GQD is classified as a relatively new molecule that attracts extraordinary interest because of its have unique in optical [1][2][3][4][5][6], electrical [7][8][9], chemical [10][11][12][13][14][15], and structural properties [16][17][18]. The optical nonlinearity of organic materials has been investigated and become a subject of extensive research to understand their intrinsic properties and their possible usage for photonic applications [8,19,20] and their potential use in photonic applications [21].…”

“…Computationally, hexagonal graphene quantum dot (GQD) which is induced by an external electric field will generate a nonlinear optical effect (NLO). As a result, The different anisotropy properties are shown when GQD is induced by an external electric field in different direction fields so that the first hyperpolarization value depends on the direction of the electric field [7]. Theoretically, it shows that the NLO response of the hexagonal GQD molecule can be electrically tuned.…”