Efficient Green Emission from Edge States in Graphene Perforated by Nitrogen Plasma Treatment

Plasma functionalization of graphene is one of the facile ways to tune its doping level without the need for wet chemicals making graphene photoluminescent. Microscopic corrugations in the two-dimensional structure of bilayer CVD graphene having a quasi-free-suspended top layer, such as graphene ripples, nanodomes, and bubbles, may significantly enhance local reactivity leading to etching effects on exposure to plasma. Here, we discovered that bilayer CVD graphene treated with nitrogen plasma exhibits efficient UV-green-red emission, where the excitation at 250 nm leads to photoluminescence with the peaks at 390, 470, and 620 nm, respectively. By using Raman scattering and spectroscopic ellipsometry, we investigated doping effects induced by oxygen or nitrogen plasma on the optical properties of single- and bilayer CVD graphene. The surface morphology of the samples was studied by atomic force microscopy. It is revealed that the top sheet of bilayer graphene becomes perforated after the treatment by nitrogen plasma. Our comprehensive study indicates that the dominant green emission is associated with the edge defect structure of perforated graphene filled with nitrogen. The discovered efficient emission appearing in nitrogen plasma treated perforated graphene may have a significant potential for the development of advanced optoelectronic materials.