Scaling of excitons in carbon nanotubes
  Light emission from carbon nanotubes is expected to be dominated by excitonic recombination. Here we calculate the properties of excitons in nanotubes embedded in a dielectric, for a wide range of tube radii and dielectric environments. We find that simple scaling relationships give a good description of the binding energy, exciton size, and oscillator strength. 
Vasili Perebeinos, J. Tersoff, and Phaedon Avouris