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.