Elastic exciton-exciton scattering in photoexcited carbon nanotubes

International audienceWe report on original nonlinear spectral hole-burning experiments in single wall carbon nanotubes that bring evidence of pure dephasing induced by exciton-exciton scattering. We show that the collision-induced broadening in carbon nanotubes is controlled by exciton-exciton scattering as for Wannier excitons in inorganic semiconductors, while the population relaxation is driven by exciton-exciton annihilation as for Frenkel excitons in organic materials. We demonstrate that this singular behavior originates from the intrinsic one-dimensionality of excitons in carbon nanotubes, which display unique hybrid features of organic and inorganic systems

Quantum efficiency of energy transfer in noncovalent carbon nanotube/porphyrin compounds

International audienceWe report on the quantum yield of excitation energy transfer in non-covalently bound nan- otube/porphyrin compounds. Evidence for energy transfer is gained from photoluminescence exci- tation experiments. We perform a quantitative evaluation of the transfer quantum yield in the case of (6,5) nanotubes through three independent methods : quantitative PLE measurements, evalu- ation of the luminescence quenching of the donor (porphyrin) and ultrafast transient absorption measurements. The latter shows a tremendous increase of the porphyrin recovery rate upon incor- poration in the compound. All these measurements consistently lead to an exceptional quantum yield efficiency

A sensing mechanism for the detection of carbon nanotubes using selective photoluminescent probes based on ionic complexes with organic dyes

The multifunctional properties of carbon nanotubes (CNTs) make them a powerful platform for unprecedented innovations in a variety of practical applications. As a result of the surging growth of nanotechnology, nanotubes present a potential problem as an environmental pollutant, and as such, an efficient method for their rapid detection must be established. Here, we propose a novel type of ionic sensor complex for detecting CNTs – an organic dye that responds sensitively and selectively to CNTs with a photoluminescent signal. The complexes are formed through Coulomb attractions between dye molecules with uncompensated charges and CNTs covered with an ionic surfactant in water. We demonstrate that the photoluminescent excitation of the dye can be transferred to the nanotubes, resulting in selective and strong amplification (up to a factor of 6) of the light emission from the excitonic levels of CNTs in the near-infrared spectral range, as experimentally observed via excitation-emission photoluminescence (PL) mapping. The chirality of the nanotubes and the type of ionic surfactant used to disperse the nanotubes both strongly affect the amplification; thus, the complexation provides sensing selectivity towards specific CNTs. Additionally, neither similar uncharged dyes nor CNTs covered with neutral surfactant form such complexes. As model organic molecules, we use a family of polymethine dyes with an easily tailorable molecular structure and, consequently, tunable absorbance and PL characteristics. This provides us with a versatile tool for the controllable photonic and electronic engineering of an efficient probe for CNT detection

Terahertz nondestructivecharacterization of optically thin wüstite layers on steel

International audienc

Exciton collision broadening in single-wall carbon nanotubes

The one-dimensionality of carriers in single-wall carbon nanotubes results in strong Coulomb interactions. Besides the non-perturbative binding of an electron-hole pair into an exciton, several time-resolved experiments have shown evidence for efficient exciton-exciton interactions. These studies have revealed that the exciton recombination is driven by an exciton-exciton annihilation mechanism. In fact such an Auger process is known to play a key role in the population relaxation of Frenkel excitons in organic materials, and especially J-aggregates and conjugated polymers. Here we show that the similarity with organic molecules breaks down for the dephasing induced by exciton-exciton interactions. We have studied the exciton dephasing by means of the non-linear optical technique of spectral-hole burning. We show that the collision broadening is surprisingly not limited by exciton-exciton Auger annihilation. We demonstrate that the coherence relaxation is determined by quasi-elastic exciton-exciton scattering within the fundamental excitonic band. This process is typical of Wannier excitons in inorganic semiconductors, while exciton annihilation is usually observed for Frenkel excitons in organic compounds. Our results reveal the unique non-linear properties of carbon nanotubes in between inorganic and organic materials