ABSTRACT
The bright exciton emission of carbon nanotubes is appealing for optoelectronic devices and fundamental studies of light-matter interaction in one-dimensional nanostructures. However, to date, the photophysics of excitons in carbon nanotubes is largely affected by extrinsic effects. Here we perform time-resolved photoluminescence measurements over 14 orders of magnitude for ultra-clean carbon nanotubes bridging an air gap over pillar posts. Our measurements demonstrate a new regime of intrinsic exciton photophysics with prolonged spontaneous emission times up to T1=18 ns, about two orders of magnitude better than prior measurements and in agreement with values hypothesized by theorists about a decade ago. Furthermore, we establish for the first time exciton decoherence times of individual nanotubes in the time domain and find fourfold prolonged values up to T2=2.1 ps compared with ensemble measurements. These first observations motivate new discussions about the magnitude of the intrinsic dephasing mechanism while the prolonged exciton dynamics is promising for applications.
ABSTRACT
Single-walled carbon nanotubes (SWCNTs) are considered for novel optoelectronic and quantum photonic devices, such as single photon sources, but methods must be developed to enhance the light extraction and spectral purity, while simultaneously preventing multiphoton emission as well as spectral diffusion and blinking in dielectric environments of a cavity. Here we demonstrate that utilization of nonpolar polystyrene as a cavity dielectric completely removes spectral diffusion and blinking in individual SWCNTs on the millisecond to multisecond time scale, despite the presence of surfactants. With these cavity-embedded SWCNT samples, providing a 50-fold enhanced exciton emission into the far field, we have been able to carry out photophysical studies for the first time with nanosecond timing resolution. We uncovered that fast spectral diffusion processes (1-3 ns) remain that make significant contributions to the spectral purity, thereby limiting the use of SWCNTs in quantum optical applications requiring indistinguishable photons. Measured quantum light signatures reveal pronounced photon antibunching (g(2)(0) = 0.15) accompanied by side-peak bunching signatures indicative of residual blinking on the submicrosecond time scale. The demonstrated enhanced single photon emission from cavity-embedded SWCNTs is promising for applications in quantum key distribution, while the demonstrated passivation effect of polystyrene with respect to the stability of the optical emission opens a novel pathway toward optoelectronic devices with enhanced performance.
ABSTRACT
Blinking and spectral diffusion are hallmarks of nanoscale light emitters and a challenge for creating stable fluorescent biomarkers or efficient nonclassical light sources. Here, we demonstrate suppression of blinking and spectral diffusion of individual single-wall carbon nanotubes by manipulation of their dielectric environment, resulting in 5-fold enhanced light emission. In addition, it was found that the characteristic slopes of the blinking power laws are largely independent of the dielectric environment in the limit of a large number of switching events. In contrast, the on/off ratio determined from statistical occurrence analysis is found to be improved by 3 orders of magnitude toward the on state, making the on/off ratio an important measure for charge transfer from/into the local dielectric environment of a quantum emitter. Furthermore, our approach is compatible with integration into cavities, in contrast to previous demonstrations of spectral diffusion suppression achieved in free-standing single-wall carbon nanotubes. This opens up possibilities to couple the exciton emission of nonblinking carbon nanotubes to cavity modes to further benefit by the Purcell effect and to enhance the light extraction efficiency, in order to ultimately demonstrate efficient photonic devices.
