Vibrational spectra of double molybdates and tungstates of the type Na5Ln(XO4)4

doi:10.1016/0022-3697(93)90005-C

Journal of Physics and Chemistry of Solids

Volume 54, Issue 9, September 1993, Pages 1005-1008

https://doi.org/10.1016/0022-3697(93)90005-C Get rights and content

Abstract

The i.r. and Raman-laser spectra of double molybdates and tungstates of stoichiometry Na₅Ln(XO₄)₄ (Ln = trivalent lanthanide cation; X = Mo or W) were recorded and analyzed by means of a factor group analysis. The results are briefly discussed.

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The complex impedance of β-Na₄Cu(MoO₄)₃ was investigated in the 573–833 K temperature range and 40 Hz–5 MHz frequency range. The Nyquist plots have been successfully analysed by an equivalent of series combination of grains and grain boundaries elements. This analysis revealed presence of two relaxation phenomena and revealed that grain boundaries cause a partial blockage of the carriers charge. We have also measured Raman and IR spectra. Based on C_2h factor group symmetry and the correlation method, the number and type of intramolecular vibrations have been predicted. We have also proposed assignment of the observed vibrational modes. Band gap energies were also determined by different methods using UV–vis–NIR diffuse reflectance spectrum. The obtained values shows that this material is a semiconductor with indirect band gap. Absorption spectrum showed presence of two strong bands. The band around 1.38 eV has been assigned to the forbidden d–d transitions of Cu²⁺ ion adopting the [4 + 2] Jahn-Teller distortion whereas that extending from 2.15 to 4.13 eV has been attributed to ligand to metal charge transfer transition.
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The bending modes of molybdate ions were observed between 260 and 400 cm−1 (387 and 322 cm−1) region. The lattice modes of K+, Gd3+, Eu3+ and Bi3+ were observed below 260 cm−1 (157 cm−1) [11]. Increasing the content of Mo (i.e.) (MoO4)2− in the double tungstate matrix gradually changes the structure, low intense new peaks starts to appear at 947 cm−1.
Nanocrystalline KGd_1−(x+y)Eu_xBi_y(W_1−zMo_zO₄)₂ was successfully synthesised via polymeric metal complex sol–gel synthesis method and the effect of Bi³⁺ and Mo incorporation in Eu³⁺:KGd(WO₄)₂ (KEGW) for red luminescence was discussed. TEM analysis confirms the nano dimension of KGW powder calcined at 650 °C. Raman spectral results demonstrate that all Eu³⁺ doped and Bi³⁺ co-doped samples did not show structural changes and Mo doped samples show structural changes from monoclinic to anorthic structure at high doping concentrations. Excitation and emission results demonstrate that 50% Eu³⁺:KGW shows high intensity red emission without substantial quenching. Further increment in the intensity was observed with Bi³⁺ co-doping in the Eu³⁺:KGW matrix. Mo incorporation in the Bi³⁺, Eu³⁺:KGW matrix shows broad CT band with high intensity and narrow red emission.
Small non-polar complexes exhibiting significant piezoelectric properties: Solvothermal synthesis and crystal structures of MO <inf>5</inf>V(tren) ·H <inf>2</inf>O (M=Mo and W; Tren=tris(2-aminoethyl)amine)
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The two isostructural complexes MO₅V(tren)·H₂O (M=Mo (1) and W (2)) were synthesized under solvothermal conditions at pH≈12 crystallizing in the non-centrosymmetric space group P2₁2₁2₁. The structures are constructed by a distorted tetrahedral [MO₄]²⁻ anion bound via one shared oxygen atom to a severely distorted [V^IVN₄O]²⁺ complex completing the octahedral coordination around the V centre. The two O atoms in the VN₄O₂ octahedron are in cis position. The two compounds represent rare examples where the [MO₄]²⁻ anion is acting as a ligand. Both compounds exhibit a piezoelectric effect which is more pronounced for M=Mo. The samples are further characterized with IR and UV/Vis spectroscopy and thermal analysis.
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Two complex molybdenum oxides, Na₅Ln(MoO₄)₄ (Ln = Gd, Er), have been prepared under high temperature solid-state reactions. The synthesized compounds have been investigated by means of the single-crystal X-ray diffraction and spectral measurements. All of the investigated structures crystallize in space group I4₁/a with Z = 4; a = 11.4720(3) Å, R₁ (residual factor for all date) = 0.0548 for Na₅Gd(MoO₄)₄; a = 11.3745(3) Å, R₁ (residual factor for all date) = 0.0514 for Na₅Er(MoO₄)₄. Additionally, the calculations of band structure, density of states, dielectric constants, and refractive indices were performed with the density functional theory method for Na₅Gd(MoO₄)₄. The results show that the solid-state compound of Na₅Gd(MoO₄)₄ is an insulator with direct band-gap of 3.695 eV, and the calculated refractive indices is 2.063 at the static case.
Potential red phosphor for UV-white LED device
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Potassium-europium double tungstate and molybdate, KEu(WO₄)₂₋_x(MoO₄)_x, has been synthesized by solid state reactions. As the molybdate content increased, the intensity of the ⁵D₀→⁷F₂ emission of Eu³⁺, activated by irradiation at 396 nm, increased and reached a maximum at a mole ratio of molybdenum to tungsten of 3. These changes were accompanied by changes in the shape of the spectra, which is associated with the crystal field splitting of the ⁵D₀→⁷F₂ transition. As the molybdenum content increased, the emission intensity at 615 nm increased and that at 620 nm decreased. This indicates the formation of a new crystal structure, rather than solid solution formation. In this study, the effects of flux, concentration of molybdate, and resulting crystal structure on the PL properties was discussed.

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^‡: Author to whom correspondence should be addressed.

^∥: On leave of absence from CSIC, Madrid, Spain.

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Vibrational spectra of double molybdates and tungstates of the type Na5Ln(XO4)4

Abstract

Struct. Bonding

J. Solid State Chem.

Spectrochim. Acta

Spectrochim. Acta

J. Phys. Chem. Solids

Russ. J. Inorg. Chem.

Sov. Phys. Crystallogr.

Sov. Phys. Crystallogr.

J. Chem. Phys.

J. Luminesc.

Inorganic Infrared and Roman Spectra

Vibrational spectra of double molybdates and tungstates of the type Na₅Ln(XO₄)₄