Single -walled carbon nanotube photophysics: Structural and environmental studies

The near-infrared band-gap emission properties of single-walled carbon nanotubes (SWCNTs) are examined in context of their physical structure and surrounding environment. A combination of optical measurements is used to characterize variations in nanotube structural distributions among different production batches. Length-dependent photophysical effects are explored in a study of more than 400 individual (10,2) nanotubes. The maximum emission intensity is found to depend linearly on length. This linear dependence is consistent with a constant E22 absorption cross-section per carbon atom and a length-independent intrinsic fluorescence quantum yield. The average intensity also is linear with length and is reduced in half from quenching defects. Emission linewidths and peak positions are measured and related to the inhomogeneity and local dielectric properties of the surrounding medium. Additional spectral shifts occur when SWCNTs are deformed with axial strain. These shifts are measured and correlated to a simple theoretical model. Important deviations that are lost in the averaging in bulk samples are revealed in spectra of individual nanotubes as they are deformed. Spectra measured from different points along the length of one nanotube confirm that these deviations result from varying load transfer and loss of matrix adhesion at localized sections of the SWCNT. Finally, the use of the NIR emission of SWCNTs to enhance biological imaging in vivo and assess a quantitative biodistribution ex vivo is demonstrated.