Temperature-dependent photoluminescence from single-walled carbon nanotubes

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of pillar-suspended single-walled carbon nanotubes has been measured for temperatures between 300 and 5 K. The atmospheric environment strongly affects the low-temperature luminescence. The PL intensity is quenched at temperatures below similar to40 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 -3x10(-5) K-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 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.