Abstract Submitted to the    NANOTUBE'06 Conference:

Nature of Optical Transitions in Carbon Nanotubes and Population Analysis

Ado Jorio

Universidade Federal de Minas Gerais

adojorio@fisica.ufmg.br

XVI. Optical Properties and Optoelectronics

The nature of the optical transitions in carbon nanotubes will be discussed, addressing the excitonic versus band-to-band photophysics, and the phonon related states. The most intense (so called $E_{ii}$) transitions are measured up to the fourth optical level in semiconducting tubes ($E_{44}^S$). Surprisingly we find that, while the first and second optical levels are excitonic, the third and fourth levels are band-to-band transitions. The exciton binding energies and their dependence on tube diameter are directly extracted from the $E_{ii}$ data. Other weak absorption/emission peaks will be addressed too, focusing on the exciton-phonon side bands. The $E_{ii}$ and $\omega_{RBM}$ are now established for all single-wall carbon nanotubes in the diameter range between 0.6 and 2.3nm, and energy range between 0.7 and 3.0eV. The intensities of the $E_{ii}$ transitions are studied for ({\it n,m}) population characterization using optics. Characterization of HiPco, CoMocat and Alcohol samples are discussed, and they suggest the preferential production of large chiral angle tubes when going to diameters below 0.9nm.

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