Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of SurfaceStates

Photoluminescence in Functionalized/Doped Graphene Quantum Dots: Role of Surface StatesIt has been shown that functionalization/doping of Graphene Quantum Dots (GQDs) can lead to further tuning of their already existing band gap. We have successfully functionalized GQDs (synthesized by hydrothermal process) with oxygen, hydrogen, fluorine, and doped with nitrogen using capacitively coupled plasma of respective gas as evidenced by Raman and X-ray photo emission spectroscopy (XPS). Room temperature photoluminescence (PL) of each functionalized GQD shows distinctive features and can be explained as due to charge transfers between the functional groups/dopants and GQDs as well as presence of mid gap states as a result of functionalization and doping. An energy diagram model is proposed to elucidate the PL modulation resulting from functionalization and doping.