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31.
CeO2-γ-Al2O3 mixed oxides have been prepared by using both co-precipitation and impregnation methods followed by calcination at 650°C and investigated by 27Al MAS NMR, powder X-ray diffraction and temperature programmed reduction techniques to understand the nature of chemical interaction existing between CeO2 and γ-Al2O3. The 27Al NMR spectra of CeO2-containing samples showed an additional peak placed at 40 ppm along with the two peaks at 68 and 6 ppm which originate from the tetrahedrally and octahedrally coordinated Al3+ ions present in γ-Al2O3. As the concentration of CeO2 in the mixed oxide increased, the intensity of the 40 ppm peak increased and this was the prominent peak for CeO2-rich mixed oxide samples. The origin of this 40 ppm peak is discussed and it is inferred that this peak is due to Al3+ ions, which are present in CeO2 lattice, forming a solid solution. 相似文献
32.
Jayshree Ramkumar V. Sudarsan S. Chandramouleeswaran V.K. Shrikhande G.P. Kothiyal P.V. Ravindran S.K. Kulshreshtha T. Mukherjee 《Journal of Non》2008,354(15-16):1591-1597
Two series of boroaluminosilicate glasses having varying mole ratios of B2O3/Na2O (series 1) and B2O3/SiO2 (series II) were prepared by conventional melt-quench method. Based on 29Si and 11B MAS NMR studies, it has been established that for series I glasses up to 15 mol% B2O3 content, Na2O preferentially interacts with B2O3 structural units resulting in the conversion of BO3 to BO4 structural units. Above 15 mol% B2O3 for series I glasses and for all the investigated compositions of the series II glasses, silicon structural units are unaffected whereas boron exist in both trigonal and tetrahedral configurations. Variation of microhardness values of these glasses as a function of composition has been explained based on the change in the relative concentration of BO4 and BO3 structural units. These glasses in the powder form can act as efficient room temperature ion exchangers for metal ions like Cu2+. It is seen that the ion exchange does not affect the boron and silicon structural units as revealed by IR studies. 相似文献
33.
S. Dhiren Meetei S. Dorendrajit Singh N. Shanta Singh V. Sudarsan R.S. Ningthoujam M. Tyagi S.C. Gadkari R. Tewari R.K. Vatsa 《Journal of luminescence》2012,132(2):537-544
White emitting nanocrystalline ZrO2:Eu3+ phosphors were synthesized by a simple precipitation route without using a capping agent. X-ray diffraction (XRD) study of ZrO2 and ZrO2:Eu3+samples revealed the presence of monoclinic and tetragonal phases. The monoclinic phase increases with increase in the annealing temperature while the tetragonal phase increases with increase in the concentration of Eu3+. This can be attributed to the presence of oxygen vacancy evolved when Zr4+ is replaced by Eu3+. Photoluminescence (PL) emission peaks of Eu3+ are observed at 591, 596, 606 and 613 nm on monitoring excitation wavelengths at 250, 286, 394 and 470 nm. The peaks at 591 and 606 nm were found to correlate with the tetragonal phase and those at 596 and 613 nm with the monoclinic phase. Intensities of these peaks are found to change as the crystal structure changes. The lifetime value corresponding to 591 nm peak increases with Eu3+ concentration at a particular heating temperature indicating increase of tetragonal phase with respect to monoclinic phase. The CIE co-ordinates of the doped samples were found to be close to that of white color (0.33, 0.33). The changes in the crystal structure of the doped samples due to doping and annealing did not affect the white color emission. 相似文献