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Exciton dans un fil quantique organique

Abstract : We have studied the excitonic luminescence of a single isolated poly-diacetylene chain, the red phase of poly-3BCMU, in its monomer matrix, by micro-photoluminescence. From the micro-photoluminescence émission lineshapes, we have first shown that, in the reciprocical lattice, the center of mass of the red exciton has to be described by a band which density of states is the one of a perfect one dimensional system. Then, we have shown that the interaction between the red exciton and the longitudinal acoustic phonons of the monomer crystal surrounding the chain ensures the thermodynamic equilibrium between the exciton and the lattice, and also governs the homogenous émission linewidth. Furthermore, starting with a quasi-1D Wannier exciton and considering the dielectric mismatch between the chain and its outside medium, we have shown that the confinement can explain the large binding energy of the red exciton. Consequently, poly-3BCMU red chains are not only a model system for the study of conjugated polymers, but also a model system in order to study the electronic properties quasi-1D Wannier excitons. We have also studied the exciton-photon interaction. Under resonant excitation, the red chain excitonic absorption is shown to saturate at high excitation power, in a regime for which the photocreated excitons are non interacting bosons. Comparing this experimental observation with the results of the calculation of the interaction between photons and excitons dressed by relaxation, we have conclude that the number of photocreated excitons tend to saturate with the excitation power when their lifetime is comparable to the period of the Rabi oscillation. Finally, we have presented the spatial emitting profile of a single isolated poly-3BCMU red chain. We have shown that the red exciton recombines over all the chain, i.e., over a characteristic length of 10 µm. Our studies show that the spatial emitting profile of a single red chain depend neither on the excitation power, nor on the position of the excitation along the chain. According to the presented images of the red chain luminescence, it seems likely that the red exciton wavefunction is delocalized over all the chain.
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Contributor : Francois Dubin <>
Submitted on : Wednesday, October 6, 2004 - 10:34:10 AM
Last modification on : Wednesday, December 9, 2020 - 3:09:18 PM
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  • HAL Id : tel-00007038, version 1

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Francois Dubin. Exciton dans un fil quantique organique. Matière Condensée [cond-mat]. Université Pierre et Marie Curie - Paris VI, 2004. Français. ⟨tel-00007038⟩

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