Easy extraction of water-soluble graphene quantum dots for light emitting diodes

Graphene quantum dots (GQDs) have attracted a large amount of attention due to their unique optoelectronic properties, which arise from the quantum confinement effect or edge effect or surface functionalization. Popular routes for designing GQDs are based on the reactions in aqueous phases, which are detrimental for integration of GQDs into optoelectronic devices. Hence, a critical challenge remains in utilizing the water-soluble GQDs for fabricating optoelectronic devices. Here we demonstrate for the first time a single step facile route to extract water-soluble GQDs into solid powder under reduced pressure for the fabrication of light emitting diodes (LEDs). The process avoids the need for post synthesis ex situ functionalization or the use of additional polymers to make GQDs hydrophobic retaining the intrinsic luminescent behavior of GQDs. The measured current-voltage characteristics of GQD-LED devices showed a significantly low turn-on voltage of similar to 2.5 V. Bias dependent electroluminescence leading to color tunability from blue to deep cyan is demonstrated.