Influence of exciton dimensionality on spectral diffusion of single-walled carbon nanotubes

We study temporal evolution of photoluminescence (PL) spectra from individual single-walled carbon nanotubes (SWCNTs) at cryogenic and room temperatures. Sublinear and superlinear correlations between fluctuating PL spectral positions and line widths are observed at cryogenic and room temperatures, respectively. We develop a simple model to explain these two different spectral diffusion behaviors in the framework of quantum-confined Stark effect (QCSE) caused by surface charges trapped in the vicinity of SWCNTs. We show that the wave function properties of excitons, namely, localization at cryogenic temperature and delocalization at room temperature, play a critical role in defining sub- and superlinear correlations. Room temperature PL spectral positions and line widths of SWCNTs coupled to gold dimer nanoantennas on the other hand exhibit sublinear correlations, indicating that excitonic emission mainly originates from nanometer range regions and excitons appear to be localized. Our numerical simulations show that such apparent localization of excitons results from plasmonic confinement of excitation and an enhancement of decay rates in the gap of the dimer nanoantennas.