1

Single-walled carbon nanotubes (SWCNTs) are promising candidates for a variety of electronic and optical applications. Optical transitions play a central role in the understanding of carbon nanotubes [1]. Both theoretical and experimental studies revealed that light absorption excites strongly correlated electron-hole pairs in semiconducting nanotubes, known as excitons, with binding energies of several hundred meV [2,3]. There is a strong debate on how much optical transitions are dominated by excitons in metallic SWCNTs as well. In general, binding energies are higher in nanotubes due to their one-dimensional character in comparison to bulk semiconductors. Theoretical calculations show that excitons exist even in metallic SWCNTs with binding energies predicted around 50 meV, depending on the nanotube chiral index (n,m) and the transition energy Eii [4,5]. Here we present results on the temperature dependence of the transition energies Eii of SWCNTs. Tunable Raman spectroscopy has been used to investigate the radial breathing mode (RBM). We performed measurements of the optical transition energy Eii at different temperatures for both metallic and semiconducting SWCNTs in the range of 300 K and 873 K