The development of new types of quantum dots (QDs) has
received increasing attention recently, as QDs can enable the fabrication
of new structures or devices with extraordinary functions
and properties to replace commonlyused semiconductor nanocrystals,
which are expensive and contain cytotoxic heavy metal
constituents. Among QDs, zero-dimensional graphene quantum
dots (GQDs) have been studied on both experimental and theoretical
fronts and show marvelous optical properties that are directly
associated with quantum confinement and edge effects [1,2]. Like
carbon based luminescence nanomaterials [3–6], the GQDs present
some fascinating characteristics that may not be observed in traditional
semiconductor quantum dots, such as low toxicity, excellent
solubility, high and stable luminescence, robust chemical inertness,
good biocompatibility and a tunable band gap. Therefore, the GQDs
have potential for light-emitting, photovoltaic, bioimaging, and a
new generation of detection applications [7,8]. Consequently, the
development of various chemical methods for controllable synthesis
of GQDs has received tremendous attention [9]. There are
two major strategies for synthesizing GQDs, i.e., top–down and