Structural and Raman Vibrational Studies of CeO

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<0.20 a solid solution Ce1−xBixO2−x/2 with fluorine structure is formed. For x ranging between 0.25 and 0.7, a tetragonal β′ phase coexisting with the FCC solid solution is observed. For x ranging between 0.8 and 0.9, a new tetragonal β phase appears. The β′ phase is postulated to be a superstructure of the β phase. Finally, close to x=1, the classical monoclinic α Bi2O3 structure is observed. Raman spectroscopy confirms the existence of the phase changes as x varies between 0 and 1

Light depolarization effects in tip enhanced Raman spectroscopy of silicon (001) and gallium arsenide (001)

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

Compositional dependence of the crystal symmetry of Eu3+-doped (SrxBa1-x)(2)CaWyMo1-yO6 phosphors

International audienceTwo series of A-site and B-site Eu3+ doped (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials were prepared via a modified Pechini sol-gel route; (SrxBa1-x)(1.96)Eu(0.02)K(0.02)CaW(y)Mo(1-)yO(6) and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Frn (3) over barm for x=0, via tetragonal 14/m for x=0.25, to monoclinic P2(1)/n for x >= 0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties. (C) 2015 Elsevier Inc. All rights reserved