Interest in the optical characteristics of carbon based nanostructures has exploded in the last decade, with advances in graphene earning the 2010 Nobel Prize. Not only is carbon extremely abundant but when in crystalline form it is among the strongest and most stable structures known to man. Quantum confinement in carbon nanostructures is sensitive to structural and environmental variations allowing for tuning of the photon emission wavelength over a wide spectrum. When combined with the potential to be used as single photon emitter, carbon nanostructures are good candidates for use in quantum cryptography and quantum computers. The fabrication of carbon based optoelectronics also has the potential to greatly lower environmental impact when compared with current technologies using gallium arsenide or metal-organic chemical vapour deposition growth.
Graphene, an atomically thick sheet of carbon, forms the basis of several important nanostructures. It can be “cut” into graphene nanoribbons (GNRs) and “rolled” into carbon nanotubes (CNTs). This introduces quasi one dimensional quantum confinement which opens a band gap enabling light emission in the form of photoluminescence (PL). The optical properties are dominated by excitonic quasi-particles whose dynamics are highly sensitive to environmental perturbations.
Our lab has recently uncovered a PL saturation effect in air-suspended CNTs caused by long range exciton-exciton interaction and annihilation. Since the exciton interaction length is so long, even at relatively low intensity ultrafast excitation creates exciton populations large enough that this effect becomes relevant and exciton-exciton annihilation (EEA) becomes abundant. The rapid collapse of an excitonic population into a single exciton shows great promise for a single photon source. With adequate study of carbon nanotubes a wavelength tunable single photon source from carbon could be close to realization.