▎ 摘　　要

Graphene oxide (GO) has attracted considerable attention due to its interesting structure and properties. The photoluminescence (PL) of GO is much stronger than that of graphene owing to the opening of an energy band gap. However, the origin of the PL bands in the ultraviolet and visible ranges remains controversial. In this paper, we report the dependence of the PL spectrum of GO on the pH value and concentration of GO aqueous solutions. It was discovered that PL in the visible range becomes prominent when the pH value is low and/or the GO concentration is high. As revealed by the time-resolved photoluminescence, the lifetime of the PL in the visible range is longer than that in the UV range. These results evidence the formation of excimers and prove that the PL band at the long wavelength is caused by the GO excimers.