Effect of defects covalent bonding in the optical absorption and electronic structure of carbon nanotubes*

Single-wall carbon nanotubes (SWCNTs) are 1D materials that show unique properties and great potential for technological applications. As a light emitter, SWCNTs show photoluminescence quantum yields in the range of 1% - 10%, which reduce their applicability. Previous theoretical and experimental studies show that sp³defects (chemical groups or atoms attached by covalent bonds) introduce local modifications to the electronic structure, creating new photoluminescent states with red-shifted energies, in the range of 100 - 300meV. This effect is caused by exciton localization at the sp³ defects.

In this work, we calculate the quasiparticle band structure, absorption spectra and excitonic properties of SWCNTs bonded to hydrogen atoms by using ab initio calculations. We first observe a split of degenerated conduction and valence bands and the appearance of a new flat impurity band. Finally, we evaluate the absorption spectra and exciton wavefunctions and its compositions. We observed a red-shift of the E₁₁ peak, associated to pristine SWCNTS, and the appearance of new red-shifted peaks associated to the impurity band.