Graphene quantum dots with controllable surface oxidation, tunable fluorescence and up-conversion emission

In this article, graphene quantum dots (GQDs) with tunable surface chemistry (increasing oxidation degree) were prepared by an efficient two-step method. The GQDs have tunable fluorescence induced by the degree of surface oxidation, fine solubility, high stability and applicable up-conversion photoluminescence (PL). The PL mechanism was investigated based on the surface structure and PL behaviors. More importantly, the GQDs have acid–base response property and can be applied as pH sensors.