Strong exciton-phonon interaction assisting simultaneous enhancement of photoluminescence and Raman scattering from suspended carbon nanotubes

We have observed intensity enhancement in exciton photoluminescence and $G$-band Raman scattering of suspended pristine semiconducting carbon nanotubes (CNTs) under resonant excitation while preventing surrounding dielectric Coulomb screening and emission quenching effects. Photoluminescence excitation (PLE) microspectroscopy for the isolated CNTs shows that the PL and Raman scattering are simultaneously enhanced when the excitation photon energy is equal to the sum of the energies of the lowest-energy bright exciton and a longitudinal optical (LO) phonon. This simultaneous enhancement is attributed to a large density of states of the lowest-energy bright exciton strongly interacting with the LO phonon at the \ensuremath{\Gamma} point. The resonant excitation is a key to understanding the excitation and emission processes of CNTs and to designing optimal photonic nanostructures applicable to efficient CNT-based light-emitting devices.