Excitation transfer and luminescence in porphyrin-carbon nanotube complexes

Functionalization of carbon nanotubes with hydrosoluble porphyrins (TPPS) is achieved by "$\pi$-stacking". The porphyrin/nanotube interaction is studied by means of optical absorption, photoluminescence and photoluminescence excitation spectroscopies. The main absorption line of the porphyrins adsorbed on nanotubes exhibits a 120 meV red shift, which we ascribe to a flattening of the molecule in order to optimize $\pi-\pi$ interactions. The porphyrin-nanotube complex shows a strong quenching of the TPPS emission while the photoluminescence intensity of the nanotubes is enhanced when the excitation laser is in resonance with the porphyrin absorption band. This reveals an efficient excitation transfer from the TPPS to the carbon nanotube

Influence de l'apport de differentes fumures sur la production des dipteres en zone non bocagere dans une parcelle conduite en monoculture de mais

*INRA, Centre de Rennes Diffusion du document : INRA, Centre de RennesNational audienc

Correlation between optical properties and barrier composition in InxGa1−xP/GaAs quantum wells

9 páginas, 11 figuras.In this work high structural and optical quality InxGa1−xP/GaAs quantum wells in a wide range of thicknesses have been successfully grown on GaAs substrates by low temperature atomic layer molecular beam epitaxy. We demonstrate that compositional fluctuations in the barrier alloy are responsible for the inhomogeneous broadening and spatial localization effects observed in the excitonic recombination, the influence of quantum well width fluctuations being negligible in comparison. An important change of the optical transition energies in these quantum wells is observed when tuning a 10% In–Ga ratio in the alloy around the lattice match composition (x=0.48). This change is related to the barrier band gap variation and the intrinsic characteristics of the InGaP/GaAs heterostructure: different exciton binding energy from tensile to compressive strain in the barrier, and a possible dependence of the conduction band offset on the In composition.The first author (J.M.-P.) wishes to acknowledge the French– Spanish cooperation Project No. HF1995-0028. This work was supported by the Spanish ‘‘CICYT’’ under Project No. TIC96-1020.Peer reviewe

A Proposal for a New Type of Prefabricated Stone Wall

International audienceThis article deals with the proposal of a stone prefabricated structure. Today, prefabrication promises convenience when applied to the construction industry, in terms of project costs abatement, ecology and final results quality. Notwithstanding, it implies some technological expedients that cannot be overlooked and that should be solved with an accurate engineering effort. Furthermore, freestone manifests qualities related to sustainable development, durability and aesthetic that lead us to want to extend this material use in contemporary architecture. Our proposal combines these issues. We present a design description of a sandwich structure in dimension stone and an analysis of its mechanical behavior that could confirm it responds positively to all the typical loading conditions of a prefabricated structure. In conclusion, we also report a record of a first constructive experimentation performed on this type of structure as a further confirmation of its efficacy

Optical study of a ZnSe/Zn0.73Mn0.27Se heterostructure

Photoluminescence, excitation spectroscopy and magneto-photoluminescence experiments are performed up to 5.5T at low temperature (1.7K) in a ZnSe/Zn0.73Mn0.27Se double quantum well. The experimental results are compared with calculations of the excitonic transitions, available for a type-I and a type-II band structure. These calculations include the strain effects, the giant Zeeman effect in the (Zn,Mn)Se layers under a magnetic field, the diamagnetic shift of the exciton. We determine the strain state of the heterostructure and find a quite unusual configuration of the band structure : the fundamental optical transitions of the two wells are type-I light hole transitions, while the excited optical transitions are type-II heavy hole transitions