Small pieces of graphene, called graphene quantum dots (GQDs), have attracted a great deal of interest from the perspective of both fundamental studies and their potential optical applications. Photoluminescence or fluorescence with a very broad emission profile covering the whole of the visible spectrum—from blue to red—is one of the intriguing properties of GQDs, and it is very useful for application in light-emitting devices and in bio-imaging.

Drastic shifts are observed by K. Matsuda and co-workers in the photoluminescence emission spectra from the UV region to the near-infrared region for different GQDs, which are separated by high-performance liquid chromatography. The mechanism behind this broad photoluminescence and its shift, dependent on the GQD properties, is also discussed.

These findings will accelerate the development of novel optical applications for GQDs in bio-labelling and light-emitting devices, as well as the progress of a basic understanding of the optical properties of carbon nanomaterials, including graphene nanostructures.