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 great potential for technological applications. Previous theoretical and experimental studies show that sp³defects introduce local modifications to the electronic structure, creating new photoluminescent states with red-shifted energies. This effect is related to an exciton localization at the sp³ defects. Those functionalized SWCNTs show higher quantum efficiency and are promising candidates for single photon emitters.

In this work, we combine GW, Bethe-Salpeter Equation (BSE) and tight binding calculations to study SWCNT covalently bonded to hydrogen atoms. Our ab-initio results show an impurity state in the middle of the gap of semiconducting SWCNTs, in which the wavefunction is spatially localized around the defect. To study more realistic systems, we explored the effect of defect concentration by using tight binding calculations, and we obtained distributions of impurity levels. In our BSE results, we observe a rich variety of bright and dark excitons and, we observed that redshifted transitions are due to excitons composed by the impurity state.

Our work relates the exciton localization with red-shifted peaks and maps bright and dark excitons that have a key role in the exciton population and lifetimes.