Double Molybdates Research Articles

Люминесценция ионов Pr-=SUP=-3+-=/SUP=- и Nd-=SUP=-3+-=/SUP=- в двойных молибдатах

AbstractThe optical spectra of samples of double zirconium molybdates activated by rare-earth Pr^3+ and Nd^3+ ions are studied. The presence of bands corresponding to the 4 f –4 f transitions of Pr^3+ and Nd^3+ trivalent ions in the absorption, excitation, and luminescence spectra is shown. A strong dependence of the luminescence intensity of Pr^3+ ions on temperature is revealed.

Determination of the g-factors measured by EPR based on theoretical crystal field and superposition model analyses for lanthanide-based magnetically concentrated crystals – case study: double tungstates and molybdates

ABSTRACTThe methods developed for theoretical determination of g-factors measured by electron paramagnetic resonance (EPR) for single transition ions are extended to lanthanide-based magnetically concentrated crystals. The crystal field (CF) and superposition model (SPM) analyses are employed for optoelectronic materials: double tungstates and molybdates. Using the crystallographic data for Nd3+ ions in RbNd(WO4)2 and Yb3+ ions in KYb(MoO4)2 as input for SPM modelling, the CF parameters (CFPs) are predicted for the respective ions. The matrix for g tensor is calculated by the complete diagonalisation method. By matching three principal g values (gxx, gyy, gzz) to those measured by EPR, three adjustable SPM intrinsic parameters:, and are obtained. The reliability of the related CFPs is verified by comparative analysis of available data. The results demonstrate that the methods suitable for single lanthanide ions in crystal can be successfully applied to magnetically concentrated systems. The predicted g tensor anisotropy enables consideration of EPR linewidths arising from dipolar broadening in ALn(MO4)2 (A = alkali ions, Ln = lanthanide ions, M = W or Mo) systems based on the moment method, which requires accurate g-factors. The model parameters determined here may be utilised for SPM/CFP calculations for Nd3+ and Yb3+ ions in single-molecule magnets and single-ion magnets.

Optical spectroscopy of molybdates with composition Ln2Zr3(MoO4)9 (Ln: Eu, Tb)

This study examined the luminescent properties of systems of double molybdates doped with Eu and Tb — this includes emission, excitation and absorption spectra. The compounds exhibited bright luminescence in the visible region due to the [Xe]4fn → [Xe]4fn transitions of rare-earth ions. The luminescence is excited both in the [Xe]4fn → [Xe]4fn bands of the rare-earth ions and in the wide band in the ultraviolet region related to the transitions within the Mo-O complex. Because of the energy transfer, the luminescence of Tb3+ and Eu3+ in doubly doped molybdates has had common excitation energies.

Simulation of Simple and Complex Gadolinium Molybdates by the Interatomic Potential Method

Crystals of ferroelectric‒ferroelastic gadolinium molybdate Gd2(MoO4)3, calcium molybdate CaMoO4, and double sodium‒gadolinium molybdates of stoichiometric (Na1/2Gd1/2MoO4) and cationdeficient (Na2/7Gd4/7MoO4) compositions, which are used to design solid-state lasers, phosphors, and white LEDs, have been simulated by the interatomic potential method. Their structural, mechanical, and thermodynamic properties are calculated using a unified system of interatomic potentials and effective ion charges, which demonstrated transferability and made it possible not only to describe the existing experimental data but also to predict some important physical and thermodynamic properties of molybdate crystals. The influence of the deviation from stoichiometry and partial ordering of cations on sites in nonstoichiometric crystals on the properties and local structure of sodium‒gadolinium molybdates is discussed.

СИСТЕМА ПОДВІЙНИХ ВОЛЬФРАМАТІВ І МОЛІБДАТІВ MR(EO4)2, M – NH4, Ag, Cu, Ti, R – ТРИВАЛЕНТНИЙ МЕТАЛ, E – Mo, W

More than 120 double tungstates and molybdates of general formula MR(EO4), where M – NH4, Ag, Cu, Tl; R – trivalent metals, E – W, Mo; R – Bi (excepting compounds contained NH4), La – Lu, Y, Sc (excepting compounds contained Cu (I)), In (excepting compounds contained NH4 and Tungsten) were isolated by co-precipitating from aqua solutions, or by solid-phase synthesis. All above mentioned compounds were studied by chemical analysis, thermogravimetry, X-ray and IR spectroscopy. Different numbers structural types were discovered into rows double tungstates and molybdates of composition MR(EO4)2: NH4R(WO4)2 – 3; NH4R(MoO4)2 – 3; AgR(WO4)2 – 4; AgR(MoO4)2 – 5; CuR(WO4)2 – 3; CuR(MoO4)2 – 5; TlR(WO4)2 – 8; TlR(WO4)2 – 11. Most wide among of its are sheyelit CaWO4, types: of KY(MoO4)2, α-KNd(WO4)2, α-KY(WO4)2, of its structural-distorting modifications and structures similar for glazerit. The calculation of meaning ΔHo298 MR(EO4)2, M – alkali metals, NH4, Cu, Ag; E – Mo, W, R – M (II) by method of Kaganyuk D.S. was executed. Dependence ΔHo298 for 300 compounds from radii ratio of mono- and trieevalent metals wаs presented in form of diagrams, it was provided possibility to unite all compounds in only system, where wide areas broadening of structural types were determinated. This diagrams is showing boundaries of structural types, is foreseeing building of unknown like that compounds and is forecasting isomorphic substitution in double tangstats and molybdates of composition MR(EO4)2. It is necessary in processes of preparation of materials for lasers, colouring luminophores, catalyzers, semiconductors, segneto- and piezoelectrics and other materials. It was designed the refined diagrams described regions of structural types of synthesized compounds existing. The formation regularities of different types of polymorphic modifications for crystal structures of the isolated compounds depending on the radii ratio of mono- and trivalent metals have been established. It was compiled a database for materials based on the studied compounds.

Single Crystals of KRE(MoO4)2, (RE‐ Ce, Pr) Obtained from Fluorides: Scheelite‐Related Structure and Luminescence

AbstractSingle crystals of double molybdates KRE(MoO4)2 (RE = Ce and Pr) have been prepared from high‐temperature melts by a facile and effective fluoride‐assisted method, and investigated by XRD, FTIR and photoluminescence (PL) spectroscopy. The results showed that the molar ratio of K/Mo in the molten solution play an important role in controlling content of the crystalline products. The crystallization fields of KCe(MoO4)2 has been found avoiding oxides admixtures. Both tetragonal scheelite‐related crystal structures have been established by means of single crystal X‐Ray diffraction. Structural motif of KPr(MoO4)2 has been established for the first time, while KCe(MoO4)2 has been reinvestigated and its crystal structure data have been refined. The excitation and emission spectra of KPr(MoO4)2 have been discussed in a light of energy transfer from a molybdate host.

Nonstoichiometry in the systems Na2MoO4–MMoO4 (M = Co, Cd), crystal structures of Na3.36Co1.32(MoO4)3, Na3.13Mn1.43(MoO4)3 and Na3.72Cd1.14(MoO4)3, crystal chemistry, compositions and ionic conductivity of alluaudite-type double molybdates and tungstates

As results of a powder XRD study of sintered samples of the systems Na2MoO4–MMoO4 (M = Co, Cd) quenched in air from 873K, the literature data on the phase formation and homogeneity ranges of nonstoichiometric double molybdates in these systems were corrected. The compounds are monoclinic alluaudite-type Na4-2xCo1+x(MoO4)3 (0.05 ≤ x ≤ 0.30) and Na4-2xCd1+x(MoO4)3 (0.10 ≤ x ≤ 0.40), orthorhombic lyonsite-type Na2-2yCo2+y(MoO4)3 (0.05 ≤ y ≤ 0.25), and triclinic Na2-2zCo2+z(MoO4)3 (0.10 ≤ z ≤ 0.40) of the Na2Mg5(MoO4)6 type. The temperature of the orthorhombic-to-triclinic phase transition was found to be 943 ± 10 K. Crystal structures of the alluaudite-type double molybdates (space group C2/c, Z = 4) with cobalt, manganese, and cadmium were determined. According to the atomic position occupations, the compositions for the crystals were found as Na3.36Co1.32(MoO4)3 (a = 12.6381(3), b = 13.4888(4), c = 7.1244(2) Å, β = 112.127(1)°,R = 0.0207), Na3.13Mn1.43(MoO4)3 (a = 12.7387(3), b = 13.6716(4), c = 7.1904(2) Å, β = 112.404(1)°, R = 0.0166), and Na3.72Cd1.14(MoO4)3 (a = 12.804(3), b = 13.913(3), c = 7.326(2) Å, β = 112.63(1)°,R = 0.0158). The crystal chemistry and compositions of the alluaudite-type molybdates and tungstates were considered and mainly one-dimensional character of the sodium-ion transport was shown for them. The measured values of the ionic conductivity of sintered samples of Na3.6M1.2(MoO4)3 (M = Mg, Ni, Zn, Cd) and Na3.6Mg1.2(WO4)3 exceeds 10−3Scm−1 at 673K.

Double molybdates of rare earth elements and zirconium

The results of the study of Ln2(MoO4)3—Zr(MoO4)2 molybdate systems, which made it possible to obtain new double molybdates, are summarized. The specific features of phase formation in double salt systems were determined and the formation of phases with the compositions given by three formulas Ln2Zr3(MoO4)9 (Ln = La—Tb), Ln2Zr2(MoO4)7 (Ln = Sm—Y), and Ln2Zr(MoO4)5 (Ln = Tb—Lu) was established. Phase diagrams of the systems were constructed and the interrelation between the composition and the structure of the obtained phases was determined; in addition, crystallographic, thermal, and dielectric characteristics of the obtained compounds were studied.

Thermodynamic properties of lanthanum molybdates

The enthalpy of solution of LаОНMoO4 and Cs2MoO4 in aqueous HCl at 298 К has been determined by solution calorimetry, and the standard enthalpy of formation of lanthanum hydroxomolybdate has been calculated. The enthalpies of solution of NaLa(MoO4)2 and Na5Lа(MoO4)4 in molybdate melt at 973 K have been determined by high-temperature melt solution microcalorimetry, and the high-temperature enthalpies of the double molybdates in the 298–1000 K range have been measured by the mixing method. The standard enthalpies of formation of the double molybdates have been calculated using data available from the literature. The low-temperature heat capacity of NaLa(MoO4)2 in the 60–300 K range has been measured on an adiabatic vacuum calorimeter. The basic thermodynamic properties of NaLa(MoO4)2, Na5Lа(MoO4)4, and LаОНMoO4 have been calculated.

White light emission materials of self‐assembled rare earth molybdates NaRe(MoO4)2 micro‐particles: the controllable synthesis, growth mechanism and luminescent properties

The tetragonally double alkaline rare earth molybdates NaRe(MoO4)2 (Re = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er) micro-particles in aqueous solution of Re(NO3)3 and Na2MoO4 were prepared hydrothermally by a facile and effective EDTA-assisted method, and investigated by XRD, SEM, FE-SEM, photoluminescence (PL) excitation and emission spectra. The results showed that the radii of Re ions, pH and the molar ratio of Re(NO3)3/Na2MoO4 in the synthesis solution play an important role in controlling sizes, morphologies and luminescent properties of the final products. And the possible formation mechanism for the bipyramid-like structure and role of EDTA were discussed in detail. The microstructure and PL property of NaYxLa1-x(MoO4)2:10%Eu3+ was investigated, and it showed that NaY0.5La0.5(MoO4)2 exhibited regular sphere-like morphology and emitted the stronger red emission with better color purity than other products. When Tm3+, Dy3+ and Eu3+ with appropriate concentrations were used as dopants to modify this bipyramid NaY(MoO4)2 material, the white light emission material of NaY(MoO4)2:1%Tm3+-11%Dy3+-0.6%Eu3+ was successfully synthesized and its CIE chromaticity coordinates is (0.33, 0.33), which is the standard white light point. These novel white-light-emitting NaY(MoO4)2:1%Tm3+-11%Dy3+-0.6%Eu3+ with single phase would be a promising material in the WLED field.

Electron paramagnetic resonance and photoluminescence of NaBi(MoO4)2 crystals doped with gadolinium ions

The results of electron paramagnetic resonance (EPR) and photoluminescence studies of large NaBi(MoO4)2 crystals grown by the low-gradient Czochralski method and doped with gadolinium ions (0.1 wt %) have been presented. It has been found from the analysis of the angular dependence of EPR spectra that the gadolinium ions enter into the crystal structure in the state Gd3+ and occupy the bismuth position. The parameters of the EPR spectra of the gadolinium ions have been calculated and the analogy has been drawn based on these data between the specific features of the incorporation of gadolinium ions into the structures of double tungstates and molybdates. The observed shift of the maximum of the photoluminescence band of the NaBi(MoO4)2 crystals doped with Gd3+ ions with respect to the spectrum of the undoped crystal suggests the influence of gadolinium ions on the formation of the bottom of the conduction band caused by the states of the (MoO4)2−.

White light emission materials of self‐assembled rare earth molybdates NaRe(MoO4)2 micro‐particles: the controllable synthesis, growth mechanism and luminescent properties

The tetragonally double alkaline rare earth molybdates NaRe(MoO4)2 (Re = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er) micro‐particles in aqueous solution of Re(NO3)3 and Na2MoO4 were prepared hydrothermally by a facile and effective EDTA‐assisted method, and investigated by XRD, SEM, FE‐SEM, photoluminescence (PL) excitation and emission spectra. The results showed that the radii of Re ions, pH and the molar ratio of Re(NO3)3/Na2MoO4 in the synthesis solution play an important role in controlling sizes, morphologies and luminescent properties of the final products. And the possible formation mechanism for the bipyramid‐like structure and role of EDTA were discussed in detail. The microstructure and PL property of NaYxLa1‐x(MoO4)2:10%Eu3+ was investigated, and it showed that NaY0.5La0.5(MoO4)2 exhibited regular sphere‐like morphology and emitted the stronger red emission with better color purity than other products. When Tm3+, Dy3+ and Eu3+ with appropriate concentrations were used as dopants to modify this bipyramid NaY(MoO4)2 material, the white light emission material of NaY(MoO4)2:1%Tm3+‐11%Dy3+‐0.6%Eu3+ was successfully synthesized and its CIE chromaticity coordinates is (0.33, 0.33), which is the standard white light point. These novel white‐light‐emitting NaY(MoO4)2:1%Tm3+‐11%Dy3+‐0.6%Eu3+ with single phase would be a promising material in the WLED field.

Brilliant IR Reflecting Yellow Colorants in Rare Earth Double Molybdate Substituted BiVO4 Solid Solutions for Energy Saving Applications

Brilliant IR reflecting yellow colorants are developed in rare earth double molybdate substituted BiVO4 solid solutions. Li0.10RE0.10Bi0.8Mo0.2V0.8O4 (RE = La, Pr, Sm, Gd, Tb, Dy, Y, Yb and Lu) pigments are prepared by a conventional solid-state reaction route and their optical, structural and morphological properties are analyzed. X-ray diffraction analysis confirms the tetragonal scheelite phase formation in the series. These pigments have a strong optical absorption in the UV-blue light wavelength region. CIE LAB color analysis shows that different hues of yellow shades are obtained in these solid solutions. The color characteristics are comparable to commercial BiVO4 pigment. Incorporation of double rare earth molybdates of La, Gd, Tb, Y and Lu into BiVO4 results in nontoxic IR reflecting cool pigments. The applicability of the developed pigment was tested on a concrete cement surface as well as on a metal panel. These pigments are composed of less toxic elements that make them favorable for energy sa...

Photoluminescence properties and energy transfer of KY1−xLnx (MoO4)2 (Ln=Sm3+, Eu3+) red phosphors

Eu3+ and Sm3+ activated double molybdates, KY1−xLnx(MoO4)2 (Ln=Sm3+, Eu3+), were synthesized by a convenient solid-state method. The photoluminescence properties, energy transfer and concentration quenching were investigated in the excitation and emission spectra. The results exhibit that with Sm3+ and Eu3+ ions co-doped into the host, the excitations around 394nm and 465nm become broader and their intensities are prominently enhanced compared to that of the single Eu3+ doped sample. The effective energy transfer from Sm3+ to Eu3+ is found to exist for Sm3+ and Eu3+ co-doped KY(MoO4)2 phosphors. Besides, with increasing Eu3+ doping concentration, the chromaticity coordinates of KY1−xLnx(MoO4)2 (Ln=Sm3+, Eu3+) approach to the NTSC standard values in a systematic way. The KY(MoO4)2:Sm3+, Eu3+ phosphors may be potentially used as red phosphors for white light-emitting diodes.

Homogeneity regions of double molybdates in the Na2MoO4-MgMoO4 system and structures of triclinic Na1.51Mg2.245(MoO4)3 and Na1.66Mn2.17(MoO4)3

In the samples of the Na2MoO4-MgMoO4 system quenched in the air at above 600°C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na4−2xMg1+x(MoO4)3 (0.05 ≤ x ≤ 0.35) and triclinic Na2−2yMg2+y(MoO4)3 (0.10 ≤ y ≤ 0.40) isostructural to previously studied Na2Mg5(MoO4)6. Sodium-magnesium molybdate of the Li3Fe(MoO4)3 structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na2Mg5(MoO4)6 structure type (space group \(P\bar 1\), Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)0.5(Na0.255□0.745)(Na0.755Mg0.245)Mg2(MoO4)3 or Na1.51Mg2.245(MoO4)3 (a = 6.9577(1) A, b = 8.6330(2) A, c = 10.2571(2) A, α = 106.933(1)°, β = 104.864(1)°, γ = 103.453(1)°, R = 0.0188); for the compound with manganese (Na)0.5(Na0.33□0.67)(Na0.83Mn0.17)Mn2(MoO4)3 or Na1.64Mn2.17(MoO4)3 (a = 7.0778(2) A, b = 8.8115(2) A, c = 10.4256(2) A, α = 106.521(1)°, β = 105.639(3)°, Γ = 103.233(1)°, R = 0.0175). The Na2Mg5(MoO4)6 structure is redetermined and it is shown that actually it corresponds to the composition Na1.40Mg2.30(MoO4)3.

Growth of Oxide Laser Crystals by Czochralski Method

The growth of series of actual laser crystals belonging to di erent structural types by the Czochralski method is presented. The primary attention is given to single crystalline compounds and their solid solutions with garnet structure (scandium-containing rare-earth garnets with general formula {LnSc}3[ScMe]2Me3O12, Me = Al, Ga) as well as with olivine (forsterite Mg2SiO4) and scheelite structure (double tungstates and molybdates with formula NaLn(TO4)2, where T = Mo or W). The broad bands of luminescence and absorption produced by activator ions in these laser hosts that appear either as a result of structural disorder (garnets, scheelites) or due to the doping by transition metal ions (chromium in forsterite) join together these representatives of di erent structural classes and determine their application in photonics. The paper considers the problems of growing of large crystals with uniform distribution of components and dopants, determination of congruently melting composition, especially in compounds with complex isomorphism. The mutual in uence of components and dopants, redistribution of ions along crystallographically non-equivalent sites in the structure, alteration of valency of transition metal ions accompanied with the change of their segregation coe cients under variation of redox conditions is discussed.

Controllable synthesis and down-conversion properties of flower-like NaY(MoO4)2 microcrystals via polyvinylpyrrolidone-mediated

Double alkaline rare-earth molybdates NaY(MoO 4 ) 2 with multilayered flower-like architectures have been successfully synthesized via hydrothermal method in polyvinylpyrrolidone (PVP)-modified processes. The crystal structure and morphology of the obtained products were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that reaction time and the amount of PVP have crucial influences on the morphology of the resulting novel microstructures. Under 450 nm excitation, Ho 3+ /Yb 3+ co-doped NaY(MoO 4 ) 2 samples exhibit 539 nm green emission and 960–1200 nm broadband near-infrared emission, corresponding to the characteristic lines of Ho 3+ and Yb 3+ , respectively. Moreover, increasing Yb 3+ doping enhances the energy transfer efficiency from Ho 3+ to Yb 3+ . Low and high-magnification SEM images demonstrate the perfect flower-like NaY(MoO 4 ) 2 prepared in the presence of PVP; Detailed TEM and HRTEM images further manifest the single-crystalline feature. • NaY(MoO 4 ) 2 flower-like microstructures were synthesized by hydrothermal method using polyvinylpyrrolidone. • Polyvinylpyrrolidone induces the growth of the NaY(MoO 4 ) 2 to form multilayered architectures. • Flowerlike NaY(MoO 4 ) 2 : Ho 3+ , Yb 3+ phosphors were investigated as a downconversion layer candidate.

Phase formation in Li2MoO4-K2MoO4-MMoO4 (M = Ca, Pb, Ba) systems and the crystal structure of α-KLiMoO4

Solid-phase interactions in Li2MoO4-K2MoO4-MMoO4 (M = Ca, Pb, Ba) systems were studied, and the subsolidus regions of these systems were triangulated. The lead and barium systems were studied in a more detailed way to discover that, along KLiMoO4-K2M(MoO4)2 (M = Pb, Ba), KLiMoO4-PbMoO4, and Li2MoO4-K2Ba(MoO4)2 quasi-binary sections, there are homogeneity regions reaching 6–11 mol % based on K2M(MoO4)2 and lead molybdate. Triple molybdates are formed in none of the systems, which is verified by experiments on spontaneous crystallization from solution in melt. Crystallization experiments yielded crystals of potassium dimolybdate and simple and double molybdates from the boundary systems. The crystal structure was solved for a hexagonal KLiMoO4 phase: (Na,K){ZnPO4}, a = 18.8838(7) A, c = 8.9911(6)A, Z = 24, space group P63, R = 0.065. The structure comprises a three-dimensional tridymite framework built by an alternation of corner-sharing LiO4- and MoO4 tetrahedra wherein voids are occupied by potassium cations.

Effect of ferroelastic domain pattern changes on the EPR spectra in TDM

This article presents polarized light microscopy studies of the ferroelastic domain structure and the analysis of electron paramagnetic resonance spectra of Cr3+ admixture ions in trigonal double molybdates. The correlation has been found between abnormal EPR lineshape and domain structure in ferroelastic phases of these crystals.

Ferroelastic Phase Transitions in Mixed KSc(MoO4)2 Based Trigonal Double Molybdates

Electron paramagnetic resonance method of Cr3+ ions was used in order to investigate disorder and structural phase transitions in mixed double trigonal molybdates K1–xRbxSc(MoO4)2 with x = 0.03, 0.1 and 0.2. The computer reconstruction of the EPR spectra allows to get information about the substitutional disorder induced by Rb+ ions in the neighbourhood of the Cr3+ probe. Through temperature EPR and polarized-ligth microscopy studies ferroelastic phase transitions in the mixed crystals have been found.