Diffusion limited photoluminescence quantum yields in 1-D semiconductors: Single-wall carbon nanotubes

摘要

Photoluminescence quantum yields and nonradiative decay of the excitonic S1 state in length fractionated (6,5) single-wall carbon nanotubes (SWNTs) are studied by continuous wave and time-resolved fluorescence spectroscopy. The experimental data are modeled by diffusion limited contact quenching of excitons at stationary quenching sites including tube ends. A combined analysis of the time-resolved photoluminescence decay and the length dependence of photoluminescence quantum yields (PL QYs) from SWNTs in sodium cholate suspensions allows to determine the exciton diffusion coefficient D = 10.7 ± 0.4 cm2s-1 and lifetime ΦPL for long tubes of 20 ± 1 ps. PL quantum yields φPL are found to scale with the inverse diffusion coefficient and the square of the mean quenching site distance, here ld = 120 ± 25 nm. The results suggest that low PL QYs of SWNTs are due to the combination of high-diffusive exciton mobility with the presence of only a few quenching sites.