Temperature behavior of the photoluminescence decay of semiconducting carbon nanotubes: The effective lifetime

The temperature dependence of the photoluminescence decay of excitons in single-walled carbon nanotubes was measured for two nanotube species, (7,6) and (7,5), representative of the two nanotube $(n-m)\mathrm{mod}3$ families. A monotonic increase of the photoluminescence lifetime with decreasing temperature is observed. The external strain induced by lowering the temperature below the freezing point of the solution leads to an overall lowering of the photoluminescence lifetime. This effect indicates that the measured lifetime is defined by the intrinsic electronic properties of carbon nanotubes and could be understood as an exchange interaction between bright and dark excitonic states. We find the lifetime to vary between 223 and $319\mathrm{ps}$ between 290 and $5\mathrm{K}$, obtained by a multiexponential fit, well in agreement with previous experiments.

Figure 1

(Color) The photoluminescence decay of the carbon nanotubes species (7,6) (a) and (7,5) (b) in SDS solution mixture with glycerol for several temperatures between 5 and $290\mathrm{K}$. The red curve is the instrumental response obtained by collecting scattered light. In order to achieve better signal-to-noise ratio, the $15.2\mathrm{MHz}$ repetition rate laser system was used.

Figure 2

(Color online) The photoluminescence decay of the carbon nanotube species (7,6) (a) and (7,5) (b) in SDS solution mixture with glycerol at 5 and $290\mathrm{K}$. In order to detect a possible longer decaying component, the lower $250\mathrm{kHz}$ repetition rate laser system was used.

Figure 3

(Color online) The photoluminescence decay of the carbon nanotubes species (7,6) (a) and (7,5) (b) in SDS solution mixture with glycerol at 5 and $290\mathrm{K}$. The lines show the best fit using a double-exponential decay [Eq. (1)] convoluted with the measured instrumental response shown in Fig. 1.

Figure 4

(Color online) Photoluminescence decay time versus temperature for the two representative nanotube species (7,6) and (7,5), obtained by the monoexponential fit. The solid arrows are guides for the eyes, while the vertical dashed arrows mark the temperature region where the external strain induced by the ice matrix occurs.