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Taoufyq A.,Aix - Marseille University | Taoufyq A.,University Ibn Zohr | Taoufyq A.,French Atomic Energy Commission | Mauroy V.,Aix - Marseille University | And 9 more authors.
Materials Research Bulletin | Year: 2015

We have investigated the chemical substitution effects on the luminescence properties under X-ray excitation of the solid solutions Ca(1-x)Cd(x)WO4 with 0 ≤ x ≤ 1. Two types of wide spectral bands, associated with scheelite-type or wolframite-type solid solutions, have been observed at room temperature. We decomposed each spectral band into several spectral components characterized by energies and intensities varying with composition x. One Gaussian component was characterized by an energy decreasing regularly with the composition x, while the other Gaussian component was only related to the tetrahedral or octahedral configurations of tungstate groups WO42- or WO66-. The luminescence intensities exhibited minimum values in the composition range x < 0.5 corresponding to scheelite-type structures, then, they regularly increased for cadmium compositions x > 0.5 corresponding to wolframite-type structures. © 2015 Elsevier Ltd. All rights reserved. Source


Taoufyq A.,Aix - Marseille University | Taoufyq A.,University Ibn Zohr | Patout L.,Aix - Marseille University | Guinneton F.,Aix - Marseille University | And 6 more authors.
Journal of Microscopy | Year: 2016

To better understand the role of crystal structures and local disorder in the photonic properties of the system (1 - x)CaWO4 - xCdWO4 with 0 < x < 1, two specific phases with compositions x = 0.5 (scheelite phase) and 0.8 (wolframite phase) have been studied by scanning and transmission electron microscopies. High-resolution electron microscopy images and image simulations, associated with X-ray diffraction data, allowed confirming the lattices and space groups I41/a and P2/c of the two scheelite and wolframite phases, at the local scale. The electron microscopy data show the existence of a high degree of crystallization associated with statistical distribution of Ca or Cd atoms on a Ca1-xCdx site in each lattice. © 2015 Royal Microscopical Society. Source


Taoufyq A.,Aix - Marseille University | Taoufyq A.,University Ibn Zohr | Taoufyq A.,CEA Cadarache Center | Taoufyq A.,Societe CESIGMA | And 9 more authors.
Journal of Solid State Chemistry | Year: 2014

In the present work, we investigate the structural, microstructural, vibrational and luminescence properties of the system (1-x)CaWO 4-xCdWO4 with x ranging between 0 and 1. Polycrystalline samples were elaborated using a coprecipitation technique followed by thermal treatment at 1000 °C. The samples were then characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy and luminescence analyses. X-ray diffraction profile analyses using Rietveld method showed that two kinds of solid solutions Ca1-xCdxWO4 having scheelite and wolframite structures, with respectively tetragonal and monoclinic crystal cells, were observed, with a biphasic system for compositions x=0.6 and 0.7. The scanning electron microscopy experiments showed a complex evolution of morphologies and crystallite sizes as x increased. The vibration modes of Raman spectra were characteristic of composition-dependent disordered solid solutions with decreasing wavenumbers as x increased. Luminescence experiments were performed under UV-laser light irradiation. The energies of emission bands increased linearly with cadmium composition x. The integrated intensity of luminescence reached a maximum value for the substituted wolframite phase with composition x=0.8. © 2014 Elsevier Inc. Source

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