Scientists have studied the infrared fluorescence of carbon nanotubes (rolled-up sheets of graphene). The frequency of infrared emission depended on the molecules bonded to the tube walls. By applying electrical potentials, they found that changes in the electron energy levels of carbon, induced by the attached molecules, were consistent with the frequency shifts. This allows the design of carbon nanotubes for bio-imaging, with tunable fluorescence by chemical modification.
The electronic origins of fluorescence in carbon nanotubes