Band-Gap Shift Transition in the Photoluminescence of Single-Walled Carbon Nanotubes

Photoluminescence (PL) from single-walled carbon nanotubes suspended in free space is shown to persist to high temperatures, at least to 425 °C. A new transition is identified, shifting the optical band gap. This transition is abrupt, is hysteretic, depends simply on the PL emission energy, and is affected by the gas atmosphere. A model is proposed to explain the transition, connecting changes in the PL to the environment.

Figure 1

(a) Photoluminescence for SWNT ensembles at various temperatures in nitrogen. (b) Temperature-programmed photoluminescence ($+5°\mathrm{C}/\min$ ramp).

Figure 2

Temperature-programmed photoluminescence in helium. (a) Cooling at $4°\mathrm{C}/\min$. (b) Heating at $4°\mathrm{C}/\min$. (c) Combined hysteresis curve (see text).

Figure 3

Hysteresis plots for different atmospheres ($4°\mathrm{C}/\min$). (a) Helium ambient. (b) Air ambient.

Figure 4

Photoluminescence dynamics after the introduction of various gases. The hot plate was fixed at 37 °C. Horizontal lines mark the introduction of a new gas.

Figure 5

Photoluminescence spectra as a function of vacuum conditions. The labels show the cryoshroud temperature, with low temperature signifying low pressure.