New red-shifted emitting states in carbon nanotubes, introduced by stable covalently-bound dopants,^1,2 are gaining attention for their potential to boost photoluminescence quantum yields,^1,2 add new functionality,³ and serve as single photon emitters.⁴  Critical to these possibilities is the demonstration of exciton localization or trapping at individual dopant sites.⁵  As a consequence of trapping, exciton dynamics are significantly altered, with photoluminescence (PL) lifetimes being extended significantly.⁴  We will present a detailed study of the emission dynamics associated with dopant states introduced by aryl diazonium functionalization of semiconducting carbon nanotubes.  Dopant-state PL lifetimes are found to increase by around a factor of 10 in comparison to E₁₁ exciton lifetimes.  Dependence of lifetimes on nanotube chirality, specific dopant, and dielectric environment will be presented and shown to exhibit a strong dependence on emission energy.  Evidence for existence of an associated dark trap state will also be given.  The results indicate multiple mechanisms for radiative and nonradiative decay.  Of particular interest relevant to PL stability is the relation of PL decay to potential exciton detrapping.  Possible contributing factors to detrapping, including detrapping energy, will be discussed.

References

1.  Ghosh, S. et al., Science, 330, 1656 (2010).

2.  Piao, Y. et al., Nature Chem., 5, 840 (2013).

3.  Kwon, H. et al., J. Phys. Chem. C, 119, 3733.

4.  Ma, X. et al., Nature Nanotech., 10, 671 (2015).

5.  Hartmann, N.F. et al., Nanoscale, 7, 20521 (2015).