Temperature-dependent photoluminescence from single-walled carbon nanotubes

Abstract

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of pillar-suspended single-walled carbon nanotubes has been measured for temperatures between 300 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The atmospheric environment strongly affects the low-temperature luminescence. The PL intensity is quenched at temperatures below $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for nanotubes in high vacuum, while nanotubes in helium ambient remain luminescent. The PL peak emission energy is only very weakly dependent on temperature, with a species-dependent blueshift upon cooling corresponding to a relative shift in bandgap of $\ensuremath{-}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ or less. The integrated peak intensities change by only a factor of 2, with linewidths showing a moderate temperature dependence. In PLE, the second absorption peak energy $({E}_{22})$ is also only weakly temperature dependent, with no significant shift and a limited reduction in linewidth upon cooling to $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In addition to the previously assigned nanotube PL peaks seen at room temperature, at least two distinct new classes of PL peaks are observed at cryogenic temperatures.