  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.

Materials Science;Applied Physics