Despite the attractive one-dimensional (1D) characteristics of carbon nanotubes 1 , their typically low luminescence quantum yield (QY), restricted because of their 1D nature 2-9 , has limited the performance of nanotube-based light-emitting devices 10,11. Here we report the striking brightening of excitons (bound electron-hole pairs) 12,13 in carbon nanotubes through an artificial modification of their effective dimensionality from 1D to 0D. Exciton dynamics in carbon nanotubes with luminescent, local 0D-like states generated by oxygen doping 14 were studied as model systems. We found that the luminescence QY of the excitons confined in the 0D-like states can be more than at least one order larger (~18%) than that of the intrinsic 1D excitons (typically ~1%), not only because of the reduced non-radiative decay pathways but also owing to an enhanced radiative

We report distinctive nonlinear behavior of photoluminescence (PL) intensities from localized exciton states embedded in single-walled carbon nanotubes (SWNTs) at room temperature. We found that PL from the local states exhibits strong nonlinear behavior with increasing continuous-wave excitation power density, whereas free exciton PL shows only weak sublinear behavior. The strong nonlinear behavior was observed regardless of the origin of the local states and found to be nearly independent of the local state density. These results indicate that the strong PL nonlinearity arises from a universal mechanism to SWNTs with sparse local states. The significant nonlinear PL is attributed to rapid ground-state depletion of the local states caused by an efficient accumulation of photogenerated free excitons into the sparse local states through one-dimensional diffusional migration of excitons along the nanotube axis; this mechanism is verified by Monte Carlo simulations of exciton diffusion dynamics.

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We studied the excitation density dependence of photoluminescence (PL) spectra of excitons and trions (charged excitons) in hole-doped single-walled carbon nanotubes.We found that the PL intensity of trions exhibited a strong nonlinear saturation behavior as the excitation density increased, whereas that of excitons exhibited a weak sublinear behavior. The strong PL saturation of trions is attributed to depletion of doped holes that are captured by excitons in the formation processes. Moreover, the effective radiative lifetime of a trion was evaluated to be approximately 20 ns.