Optical study on single-layer photoluminescent graphene oxide nanosheets through a simple and green hydrothermal method

Single-layer and colloidal graphene oxide (GO) nanosheets were produced by a facile and low-cost hydrothermal route using only water as the solvent. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images indicated that the obtained GO nanosheets are single-layer with an average diameter of similar to 1 nm. The GO nanostructures display relatively good quantum yield (about 3% at the excitation wavelength of 360 nm) and nearly excitation-independent PL spectrum. Four types of oxygen-containing functional groups (COOH, C-O, C-O-C, and C=O) that affect the fluorescence of GO nanosheets were confirmed by the FTIR spectroscopy. Considering the material response to the electromagnetic wave in the infrared region, we calculated optical constants of the obtained GO nanosheets using Kramers-Kronig relations. The constants include the refractive index, n(omega), and the extinction coefficient, k(omega), which are the real and imaginary parts of the complex function of the refractive index. The most important results are that the C=O vibrational energy is maximum and occurs at higher frequencies, and the maximum refractive index is related to the C-O bond.