Search

Working document; A solid solution Ce(2-x)Sm x(WO4)3 with x≤0.3 was synthesized via a coprecipitation route followed by thermal treatment at 1000 °C. The polycrystalline compounds were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence experiments. Using Rietveld procedure, the decrease of cell parameters showed that a solid solution was obtained. A comparative analysis of diffraction profiles allowed determining structural distortions increasing with composition x. Photoluminescence (PL) experiments were performed under UV and X-ray excitations. The variations with composition x of PL emission intensities, corresponding to complex charge transfers and quenching effects, were interpreted in terms of transitions proper to Ce3+ and Sm3+ cations, accompanied by additional transitions probably due to oxygen vacancies and other point defects generated by substitution and synthesis conditions. The CIE chromaticity diagrams showed variable colors located in the orange-red range.

International audience; Synthesis characterization and hydrogenation behaviour of as quenched Ti 41.5+X Zr 41.5-X Ni 17 (x=0, 3.5, 11.5 and 13.5) nano quasicrystalline ribbons-Lunar Luminescence-Luminescent properties of alumina ceramics doped with chromium oxide-This content was downloaded from IP address 147.94.103.164 on 12/10 Abstract. In this work, a study of the role of chemical substitution in the properties of the solid solution Sr 1-x Pb x WO 4 (x = 0, 0.5 and 1) is presented. Polycrystalline samples were synthesized by solid state reaction at 1100°C. Using Rietveld method, the structural parameters of all samples were refined. All structures are of scheelite type Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. The Infrared and Raman spectroscopies were performed to characterize the evolution of vibrational modes with composition x. Finally, a systematic study of luminescence under X-ray and UV excitations was performed. The energies and intensities of luminescence depended on composition x and on the nature of excitations. 1. Introduction The first paragraph after a heading is not indented The scheelite tungstate crystals AWO 4 are characterized by tetragonal structures [1,2] (space group I4 1 /a), with tetrahedral oxyanions WO 4 2-and M 2+ cations forming MO 8 groups [3]. They were extensively investigated for their potential applications as laser host materials [4,5], scintillators [6,7], oxide ion conductors [8], materials for microwave applications [9] and magnetic materials [10]. The luminescent properties under different excitations of single-crystals as well as polycrystalline SrWO 4 and PbWO 4 compounds have been widely studied by several authors [11-15]. Generally, luminescence spectra of scheelite tungstate were decomposed into two main blue and green bands, and to a weaker orange-red emission: the emissions were observed with energies close to 3.0-2.8, 2.7-2.4 and 2.3-2.0 eV [16-20]. In this work we study the luminescent properties of lead and strontium tungstates Sr 1-x Pb x WO 4 for the three compositions x= 0 ; 0.5 and 1 under X-ray and UV excitations. We already published the synthesis, characterization and luminescence under X-ray excitation of Sr 1-x Pb x WO 4 and Ca 1-x Cd x WO 4 solid solutions [21-23]. Presently, we compare the luminescence responses under X-ray and UV excitations of these substituted samples.

We report on the effects of light depolarization induced by sharp metallic tips in Tip-Enhanced Raman Spectroscopy (TERS). Experiments on Si(001) and GaAs(001) crystals show that the excitation field depolarization induces a selective enhancement of specific Raman modes, depending on their Raman tensor symmetry. A complete polarization analysis of the light backscattered from the tip confirms the TERS findings. The spatial confinement of the depolarization field is studied and its dependence on the excitation wavelength and power are explored.

Tip-Enhanced Raman Spectroscopy (TERS) is a very promising ana- lytical technique for high sensitivity, high spatial resolution analysis of the physical and chemical properties of nanoscale materials including nanocrystals, biomolecules, carbon-based nanostructures and nanometer-size devices. Polarized TERS, in addi- tion, offers novel opportunities for high contrast spectroscopy and imaging of semiconductor crystals and crystalline nanostructures. This chapter reviews the cur- rent state-of-the-art in polarization-sensitive TERS focusing the attention on the experimental implementations of the technique, on the light scattering properties of the metallic probes, on the Raman signal enhancement mechanisms and, finally, on the applications of this technique.

We report on tip enhanced Raman spectroscopy of GaAs(100) crystals taking advantage of the fields polarization to maximize the near-field contrast. Excitation parallel to either the [100] or the [110] crystallographic axis provide minimum far-field background provided that cross-or parallel-component of the Raman field are detected. Experiments highlight a tip-induced selective enhancement of the one-phonon longitudinal optical mode with respect to the transverse optical mode. We interpret this effect in terms of depolarization of the excitation field and beam deflection which breaks the polarization-based selection rules of the Raman scattering.

A series of ceramics samples belonging to the CeO2-Bi2O3 phase system have been prepared via a coprecipitation route. The crystallized phases were obtained by heating the solid precursors at 600∘C for 6 hours, then quenching the samples. X-ray diffraction analyses show that for x