Researchers observed a bright and narrow band emission of red light from individual graphene nanoribbons, only 7-atom-wide, at a high intensity comparable to bright light-emitting devices made from carbon nanotubes. Optical emission was up to 10 million photons per second, about 100 times more intense than the emission measured for previous single-molecular optoelectronic devices.
The energy shift of the main peak changes as a function of the voltage, which provides a way to tune the color of the light.
The researchers will investigate the impact of defects and GNR aspect ratio (width) on emission. They want to integrate graphene nanoribbons devices into larger circuitry to create bright, robust, and controllable graphene-based light-emitting devices.
Thanks to their highly tunable band gaps, graphene nanoribbons (GNRs) with atomically precise edges are emerging as mechanically and chemically robust candidates for nanoscale light emitting devices of modulable emission color. While their optical properties have been addressed theoretically in depth, only few experimental studies exist, limited to ensemble measurements and without any attempt to integrate them in an electronic-like circuit. Here we report on the electroluminescence of individual GNRs suspended between the tip of a scanning tunneling microscope (STM) and a Au(111) substrate, constituting thus a realistic optoelectronic circuit. Emission spectra of such GNR junctions reveal a bright and narrow band emission of red light, whose energy can be tuned with the bias voltage applied to the junction, but always lying below the gap of infinite GNRs. Comparison with ab initio calculations indicates that the emission involves electronic states localized at the GNR termini. Our results shed light on unpredicted optical transitions in GNRs and provide a promising route for the realization of bright, robust, and controllable graphene-based light-emitting devices.