Triplet Exciton Production and Lifetimes in Single-Wall Carbon Nanotubes

Despite a broad body of spectroscopic work on the photophysics of singlet excitons in SWNTs, triplet states and triplet–triplet interactions have mostly remained elusive. Here we report on the first spin sensitive study of triplet excitons in (6,5) SWNTs giving triplet lifetimes and the quantum yield of triplet exciton production using optically detected magnetic resonance (ODMR) [1]. SWNT samples were fabricated from aqueous suspensions and PFO-BPy dispersed CoMoCAT SWNTs. Triplet lifetimes of (30±10) µs were obtained from the modulation frequency dependence of ODMR signals at small excitation intensities. The yield of triplet exciton production of (5±2)% is determined using the intensity dependence of triplet-triplet annihilation, a process that competes with triplet decay as well as with non-radiative singlet decay. The results imply that steady state triplet concentrations in SWNTs are about 5 orders of magnitude higher than those of singlet excitons.

[1] D. Stich, F. Späth, H. Kraus, A. Sperlich, V. Dyakonov and T. Hertel, Nature Photonics, in press (DOI: 10.1038/NPHOTON.2013.316)