Chirality-dependent concentration boundaries of single-wall carbon nanotubes for photoluminescence characterization and applications

Increasing the concentration of single-wall carbon nanotubes (SWCNTs) is an effective method for enhancing their luminescence intensity. However, an increase in the concentration of SWCNTs would inevitably increase their reabsorption effect, degrading their luminescence efficiency. Herein, we systematically investigated variations in the photoluminescence (PL) intensity of (6,5) single-chirality SWCNTs while increasing their concentration. The results show that the PL intensity first increased to a maximum and then decreased with increasing concentration. Numerical analysis indicates that the concentration boundary corresponding to the maximum PL intensity was strongly dependent on the ratio of the optical absorbances of the SWCNTs at their excitation and emission wavelengths. According to this, statistical analysis by experimentally measuring the optical absorption spectra of 18 kinds of single-chirality SWCNTs shows that the concentration boundaries of SWCNTs were dependent upon their Types and diameters. The concentration boundary of Type I SWCNTs was higher than that of Type II SWCNTs, and the concentration boundaries of both Types increased with increasing diameter. These results provide important guidance for spectral characterization and applications in bioimaging and photoelectronic devices.