Triplet–triplet exciton dynamics in single-walled carbon nanotubes

Abstract

Semiconducting single-walled carbon nanotubes (SWNTs) are considered as building blocks for novel optoelectronic and photonic devices. Energy transport, dissipation and nonlinear optical properties of such devices depend critically on the dynamics of singlet and triplet excitons. However, little is known about triplet excitons in SWNTs despite their important role in photovoltaic, photoelectric and other applications. We present pump–probe and spin-sensitive photoluminescence studies of semiconducting SWNTs that allow the determination of the quantum yield of triplet formation (5 ± 2%), the triplet lifetime (30 ± 10 µs) and the triplet exciton size (0.65 nm). Triplet–triplet annihilation is also found to induce delayed fluorescence. The power-law decay of pump–probe and time-resolved photoluminescence signals is characteristic of diffusion-limited annihilation in one-dimensional systems and allows an estimation of the triplet diffusion constant of 0.1 cm2 s−1. This work suggests that exciton annihilation in SWNTs is reduced by one-dimensional confinement of diffusive exciton motion. Little is known about triplet excitons in semiconducting single-walled nanotubes, despite their importance in various applications. The pump–probe and spin-sensitive photoluminescence of such nanotubes is studied, and the quantum yield of triplet formation, triplet lifetime and triplet exciton size are found to be 5 ± 2%, 30 ± 10 µs and 0.65 nm, respectively.