Electroluminescence from graphene quantum dots prepared by amidative cutting of tattered graphite.

Size-controlled graphene quantum dots (GQDs) are prepared via amidative cutting of tattered graphite. The power of this method is that the size of the GQDs could be varied from 2 to over 10 nm by simply regulating the amine concentration. The energy gaps in such GQDs are narrowed down with increasing their size, showing colorful photoluminescence from blue to brown. We also reveal the roles of defect sites in photoluminescence, developing long-wavelength emission and reducing exciton lifetime. To assess the viability of the present method, organic light-emitting diodes employing our GQDs as a dopant are first demonstrated with the thorough studies in their energy levels. This is to our best knowledge the first meaningful report on the electroluminescence of GQDs, successfully rendering white light with the external quantum efficiency of ca. 0.1%.