All GO materials exhibited similar characteristic UV-Vis absorbance (Figure ) and fluorescence emission (Figure ) spectra, as revealed by the respective calibration curves that were obtained (Figures ). The absorbance measurements indicated a highly linear correlation between the concentration of GO and the absorbance at 230 nm, which is assigned to π → π* transitions in sp 2 clusters . A shoulder peak at 300 nm could also be identified, and is associated with n → π* transitions of free electron pairs in the oxygen atoms in C=O bonds, present in carbonyl and carboxyl groups . On the other hand, the fluorescence emission from GO was broad and reproducible for all three types, ranging from 400 to 800 nm with an emission peak around 600 nm. The similar calibration curves obtained for all 3 dispersions indicated that the production steps did not affect significantly the optical properties of GO.