 Temperature
is found to have a significant effect on the PL intensity of carbon nanotubes.
Emission is controlled by the 1-D nature of the excitons which causes the
intensity to increase as 1/(T)1/2 until at very low temperures the
excitons begin to fall into the so-called 'dark exciton' state, where emission
is forbidden. The peak of the intensity occurs when the temperature
corresponds to the energy splitting between the bright and dark exciton states.
This splitting is found to depend strongly on the chiral indices of the
different nanotubes as is shown in the figure. The application magnetic fields
causes a mixing between the dark and light excitonic states and this causes the
PL intensity to increase..
Fig : Temperature dependence of the PL intesity for a series
of different nanotubes, measured from PLE maps, as shown in the inset.
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