(503c) Intrinsic and Extrinsic Factors Which Affects the Optical Properties of Individual Single-Walled Carbon Nanotubes

Multiple studies have shown that the optical properties of single-walled carbon nanotubes (SWNTs) are excitonic in nature.(1-3) However, a complete understanding of how these excitonic states shape the optical properties of SWNTs is lacking. Comparing the results of different published studies is difficult; the luminescence properties of SWNTs are affected by various extrinsic factors originating from synthesis and processing methods which affect the structure, sidewall quality, and environment of SWNTs. Fundamental and applied reports are hindered by poor control over the synthesis and post-processing methods. This is highlighted by the range of reported fluorescence quantum yields and luminescence lifetimes measured from ensembles or single SWNTs ? they range between 10-4 to 7 % (4-8) and from 5 to 200 ps,(5,8-10) respectively, depending on the report.

Here we use single molecule imaging and time resolved spectroscopy, photoluminescence maps, UV-vis absorbance, and Raman spectroscopy at multiple excitation wavelengths to identify different extrinsic factors which deeply influence the optical properties of SWNT.11,12 Single molecular studies of individual (6,5) SWNTs showed that SWNT luminescence depends strongly on extrinsic and intrinsic factors such as sample preparation, sample environment, sidewall defects, and tube synthesis methods (HiPco or CoMoCat).(11) More precisely, we showed that surfactant selection and sample medium are crucial factors to obtaining SWNTs with optimum optical properties.

Ensemble measurements showed compelling spectroscopic evidence of substantial differences in chirality and diameter distribution which alter the luminescence properties within different HiPco batches.(12) These variations also affect SWNT solubility both in surfactant suspensions and superacids.

These findings underline the necessity for more standard production and post-processing procedures such that correlations between different reports in the literature can be drawn, and we begin to understand the complex excitonic structure of SWNTs.

References

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5. Wang, F.; et.al. Nano Lett. 2007, 7, (12), 3698-3703.

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10. Hirori, H.; et.al. PRL 2006, 97, (25), 257401.

11. Duque, J. G.; et.al. Nano Lett.; Submitted.

12. Duque, J. G.; et.al. In Preparation.