Gamma ray shifted and enhanced photoluminescence of graphene quantum dots

We demonstrate how the emission of graphene quantum dots with a surface consisting of hydroxyl and quinone groups is tuned from green to blue by gamma-ray irradiation ranging from 0 to 500 kGy and in the presence of radical scavengers. The photoluminescence quantum yield increases from 13 to 52% under optimal irradiation conditions. Gamma-ray irradiation triggered radicals either oxidize or reduce the surface groups of graphene quantum dots altering their chemical structure, reducing surface traps and enhancing the emission. The resulting chemical composition of surface groups derived from XPS analysis influences emission pathways and trap formation. Furthermore, the irradiated nanoparticles show a better performance and cell viability in bioimaging applications as compared to the pristine graphene quantum dots.