11 research outputs found
Exciton and interband optical transitions in hBN single crystal
Near band gap photoluminescence (PL) of hBN single crystal has been studied
at cryogenic temperatures with synchrotron radiation excitation. The PL signal
is dominated by the D-series previously assigned to excitons trapped on
structural defects. A much weaker S-series of self-trapped excitons at 5.778 eV
and 5.804 eV has been observed using time-window PL technique. The S-series
excitation spectrum shows a strong peak at 6.02 eV, assigned to free exciton
absorption. Complementary photoconductivity and PL measurements set the band
gap transition energy to 6.4 eV and the Frenkel exciton binding energy larger
than 380 meV
Nanoparticulate ZrO2/SO42- Catalyst for Biofuel Production
This study reports on the preparation of zirconia coatings based on monodispersed zirconium-oxo-alkoxy (ZOA) nanoparticles for conversion of free fatty acid (FFA) into biofuel. Monodispersed ZOA nanoparticles of 3.6 nm size were prepared by sol-gel method in a rapid micro-mixing reactor with turbulent fluids flow at 20°C. The ZOA nanopowders obtained after precipitation and nanocoatings deposited on glass beads, after subsequent sulfatation, drying and calcinations, show high catalytic activity towards esterification process. The biofuel yield in esterification of palmitic acid in methanol reached 67% (after t=3.5 hours) on nanopowders while it increases to 98% on nonocoatings
Photoluminescence of hexagonal boron nitride: effect of surface oxidation under UV-laser irradiation
International audienceWe report on the UV laser induced fluorescence of hexagonal boron nitride (h-BN) following nanosecond laser irradiation of the surface under vacuum and in different environments of nitrogen gas and ambient air. The observed fluorescence bands are tentatively ascribed to impurity and mono (VN), or multiple (m-VN with m = 2 or 3) nitrogen vacancies. A structured fluorescence band between 300 nm and 350 nm is assigned to impurity-band transition and its complex lineshape is attributed to phonon replicas. An additional band at 340 nm, assigned to VN vacancies on surface, is observed under vacuum and quenched by adsorbed molecular oxygen. UV-irradiation of h-BN under vacuum results in a broad asymmetric fluorescence at ~400 nm assigned to m-VN vacancies; further irradiation breaks more B-N bonds enriching the surface with elemental boron. However, no boron deposit appears under irradiation of samples in ambient atmosphere. This effect is explained by oxygen healing of radiation-induced surface defects. Formation of the oxide layer prevents B-N dissociation and preserves the bulk sample stoichiometry
temperature dependance of the titanium oxide sols precipitation kinetics in the sol-gel process
International audienc
Microstructure and optical properties of alumina sintered from various phases
International audienc
Antibacterial activity of ZnO and CuO nanoparticles against gram positive and gram negative strains
International audienc
Morphology and luminescence of MgAl2O4 ceramics obtained via spark plasma sintering
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