Surface relaxation determine the band bending and special optical properties of carbon nanodots

Abstract

Carbon nanodots (CDots) are frequently adopted to modify composite photocatalysts, due to their unique optical properties and adjustable band structure. Here, an ab initio approach based on extend Hückel theory is used to study in detail the dependent relationship between the optical properties of carbon nanodots and surface relaxation. In order to imitate the surface structure of carbon nanodots, a number of two-layer tiny carbon domains are used. The energy level distribution shows a clear band gap, demonstrating the features of semiconductor. The band structure is somewhat bent as a result of surface relaxation's dramatic effect on the highest occupied molecular orbital (HOMO). The ultraviolet and visible absorption spectra of carbon nanodots are successfully predicted in theory, by considering the oscillator strength in every possibility transition, and the transition from the valence band maximum (VBM) to conduction band minimum (CBM) is the main peak location. The surface relaxation results in red shift of the spectral lines, which is the potential reason why carbon nanodots promote visible light absorption.