Strong and stable photoluminescence from the semiconducting inner tubes within double walled carbon nanotubes

We examined the optical features of single wall carbon nanotubes (SWNTs) and the inner tubes within double walled carbon nanotubes (DWNTs) having the same (n,m) chirality. The brighter and more stable photoluminescence signals as well as the larger absorbance were observed for the semiconducting inner tubes within DWNTs and not for SWNTs. The outer layers of DWNTs maintain the high structural integrity of the inner tubes during both oxidative purification and strong sonication steps and are responsible in increasing the dielectric screening (due to weaker Coulomb interaction); thus leading to a redshift of the E11S and E22S excitonic transitions.