Synthesis and Characterization of Niobium Substituted Hexagonal Tungsten Bronzes

Alkali metal tungsten bronzes, M_xWO₃, and its niobium substituted forms, M_xNb_yW_1‐yO₃, have been prepared with M = K and Rb and nominal compositions of x = 0.20, 0.25, 0.30 and 0.0 ≤ y ≤ 0.20 at temperatures between 600 and 900?C. The X‐ray powder patterns reveal that single phases of niobium substituted hexagonal tungsten bronze (HTB) can be prepared for x = 0.2, y ≤ 0.05 ; x = 0.25, y ≤ 0.125 and x = 0.3, y ≤ 0.15. Investigations of the optical reflectivity and the infrared absorption of Rb_0.3Nb_yW_1‐yO₃ indicate a decreasing concentration of free carrier with increasing niobium content.     

Pressure‐induced Changes of the Crystal Structure of Eu4P3

Pressure‐induced structural changes and electronic properties of rhombohedral Eu₄P₃ were characterised by means of X‐ray powder diffraction and X‐ray absorption spectroscopy at the Eu L_III threshold. The measurements at low pressures indicate oxidation states of the europium atoms which are compatible with a composition Eu₃²⁺Eu³⁺P₃. At a pressure of 8(1) GPa, Eu₄P₃ undergoes a structural phase transition. The cubic high pressure modification with (anti‐)Th₃P₄ type crystal structure is also identified as a compound with a non‐integer average oxidation state of the europium atoms.     

A Series of Lanthanide Metal–Organic Frameworks with Interesting Adjustable Photoluminescence Constructed by Helical Chains

Based on the isonicotinic acid (HIN=pyridine‐4‐carboxylic acid), seven lanthanide metal–organic frameworks (MOFs) with the formula [Ln(IN)₂L] (Ln=Eu ( 1 ), Tb ( 2 ), Er ( 3 ), Dy ( 4 ), Ho ( 5 ), Gd ( 6 ), La ( 7 ), L=OCH₂CH₂OH) have been synthesized by mixing Ln₂O₃ with HIN under solvothermal conditions, and characterized by single‐crystal X‐ray diffraction, powder X‐ray diffraction, infrared spectroscopy, and fluorescence spectroscopy. Crystal structural analysis shows that compounds 1–6 are isostructural, crystallize in a chiral space group P2₁2₁2₁, whereas compound 7 crystallizes in space group C2/c. Nevertheless, they all consist of new intertwined chains. Simultaneously, on the basis of the above‐mentioned compounds, we have realized a rational design strategy to form the doped Ln MOFs [(Eu_xTb_1?x)(IN)₂L] (x=0.35 ( 8 ), x=0.19 ( 9 ), x=0.06 ( 10 )) by utilizing Tb^III as the second “rare‐earth metal”. Interestingly, the photoluminescence of [(Eu_xTb_1?x)(IN)₂L] are not only adjustable by the ratios of Eu/Tb, but also temperature or excitation wavelength.     

Formation of Eu2O3 Nanorods through Solvothermal Routes by Surfactant Assistance

Eu₂O₃nanorods were synthesized and characterized. The crystallites of Eu₂O(CO₃)₂·H₂O nanorods and Eu₂O₃ nanorods were obtained by means of surfactant assistance, with aqueous butanol solution as the solvent and hexamethylene tetramine as the base. The characteristics of the nanorods were analyzed by transmission electron microscopy, high‐resolution transmission electron microscopy, scanning electron microscopy and X‐ray diffraction. The Eu₂O₃ nanorod is about 80–300 nm in diameter and 1–5 µm in length. The formation mechanism of the 1D products was also proposed.     

Structural and spectroscopic investigations on the quenching free luminescence of europium oxalate nanocrystals

The structural features leading to the intense quenching free luminescence exhibited by europium oxalate nanocrystals, poly[[hexaaquatri‐μ₂‐oxalato‐dieuropium] 4.34‐hydrate], {[Eu₂(C₂O₄)₃(H₂O)₆]·4.34H₂O}_n, is the focal point of this report. Europium oxalate nanocrystals were synthesized by a simple microwave‐assisted co‐precipitation method. Powder X‐ray diffraction analysis revealed the monoclinic structure of the nanocrystals and the phase purity. The morphology and particle size were examined by transmission electron microscopy (TEM) analysis. Luminescence measurements on a series of samples of La_2–xEu_x(C₂O₄)₃·10H₂O, with x varying in the range 0.1 to 2, established the quenching free nature exhibited by the europium oxalate nanocrystals. A single‐crystal structure analysis was carried out and the quenching free luminescence is explained on the basis of the crystal structure. A detailed photoluminescence characterization was carried out using excitation and emission studies, decay analysis, and CIE coordinate and colour purity evaluation. The various spectroscopic parameters were evaluated by Judd–Ofelt theoretical analysis and the results are discussed on the basis of the crystal structure analysis.     

Tunable white light-emission of a CaW1?x Mo x O4:Tm3+, Tb3+, Eu3+ phosphor prepared by a Pechini sol–gel method

A white light-emitting CaW_1?x Mo _x O₄:Tm³⁺, Tb³⁺, Eu³⁺ phosphor was prepared by a Pechini sol?Cgel method. The incorporation of Mo⁶⁺ into the CaWO₄ host matrix can broaden its excitation range and promote tunability to its emission. When the CaW_1?x Mo _x O₄ system is triply-doped with Tm³⁺, Tb³⁺, and Eu³⁺ ions, energy transfer occurs from both WO₄ ^2? and MoO₄ ^2? groups to Tm³⁺ and Tb³⁺ ions. A significant red-shift in the excitation of Eu³⁺ allows the resulting emission to be tunable between cool, natural, and warm white light by varying the excitation wavelength. The undoped and triply-doped CaW_1?x Mo _x O₄ phosphors were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence excitation and emission spectra, and CIE chromaticity (x, y) coordinates.     

Self‐Assembly of Polyoxometalate‐Supported Ln‐H nydroxo/Oxo Clusters with 1D Extended Structure: [LnIII(H2O)7Cr(OH)6Mo6O18]n·4nH2O (Ln = Ce,Sm, Eu)

Three novel polyoxometalate compounds consisting of Anderson‐type anions and trivalent lanthanide cations, [Ln(H₂O)₇Cr(OH)₆Mo₆O₁₈]_n·4nH₂O (Ln = Ce 1 ; Sm 2 ; Eu 3 ), have been synthesized in aqueous solution and characterized by single crystal X‐ray diffraction, elemental analyses, IR spectra, and TG analyses. Single crystal X‐ray diffractions reveal that the structures of the 1:1 composite compound formed by the heteropolyanion [Cr(OH)₆Mo₆O₁₈]^3? as the building unit and the [Ln(H₂O)₇]³⁺ complex fragment as the linker, which exhibit a type of zig‐zag chain with alternating cations and anions through the Mo‐Ot′‐Ln‐Ot′‐Mo linkage in the crystal. The magnetic properties of 1 ? 3 have been studied by measuring their magnetic susceptibility over the temperature range of 2‐300 K. The UV‐vis spectra of 1 give the Mo‐O and Cr^III‐O charge transfer transitions at 203 and 543 nm, respectively. In addition, the fluorescent characteristic transition of the Eu³⁺ ions in compound 3 is reported.     

Cerium Complex with Four Types of Ligands: (NH4)6[Ce(H2W12O40)(C4H2O4)(NO3)(H2O)3]

A novel polymer (NH₄)₆[Ce(H₂W₁₂O₄₀)(C₄H₂O₄)(NO₃)(H₂O)₃] ( 1 ) has been constructed at room temperature and characterized by single crystal X‐ray structural analyses, elemental analyses, cyclic voltammetry, IR spectrum, and thermogravimetry. X‐ray structural analysis reveals that through the W–Ot′–Ce–Ob–W linkages a one‐dimension infinitely linear chain with alternating cations and anions is formed. 1 represents the first characterized compound that the Ce³⁺ ions are coordinated by four different types of ligands, and maleinate as ligands in constructing LnPOM architecture.     

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum‐Supported Cerium‐Zirconium Oxide Three‐Way Catalyst Particles by Hard X‐ray Spectro‐Ptychography

The cerium density and valence in micrometer‐size platinum‐supported cerium–zirconium oxide Pt/Ce₂Zr₂O_x (x=7–8) three‐way catalyst particles were successfully mapped by hard X‐ray spectro‐ptychography (ptychographic‐X‐ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic‐XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce₂Zr₂O_x particles. Ptychographic‐XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.     

Investigation of Luminescence Properties of Eu3+, Dy3+ and Gd3+ Doped MgAl2Si2O8 Red‐emitting Phosphors

Rare‐earth‐doped aluminosilicates of alkaline earth MgAl₂Si₂O₈: Eu³⁺, Dy³⁺ and MgAl₂Si₂O₈: Eu³⁺, Gd³⁺ were synthesized by the solid state reaction method at 1300 ^oC. The phosphors were characterized by X‐ray powder diffraction (XRD), photoluminescence (PL), thermoluminescence (TL) and scanning electron microscopy (SEM). X‐ray powder diffraction studies show that the phosphors were crystallized in the triclinic crystal system. The phosphors show characteristic broad band phosphorescence of Eu³⁺. This broad band phosphorescence has red emission bands in the range of 580–705 nm corresponding to ⁵D₀ → ⁷F_j (j:0,2,3,4) transitions of Eu³⁺.     

1D Polyoxometalate‐based Inorganic‐Organic Hybrid Derived from ß‐Octamolybdate — Synthesis and Crystal Structure of [CoII(2, 2′‐bipy)2]2[Mo8O26]

A polyoxometalate‐based inorganic–organic hybrid compound [Co^II(2, 2′‐bpy)₂]₂[Mo₈O₂₆] ( 1 ) was synthesized by hydrothermal methods and structurally characterized by IR spectrum, TG analysis and X‐ray diffraction. The compound crystallizes in the monoclinic system, space group P2₁/n, a = 10.0681(2), b = 16.4467(2), c = 15.7838(3) Å, β = 100.046(1)°, V = 2573.52(8) ų, Z = 2. The structure of 1 is built up from β‐[Mo₈O₂₆]^4? subunits covalently linked via [Co^II(2, 2′‐bpy)₂]²⁺ fragments into a infinite 1D {[Co^II(2, 2′‐bpy)₂]₂[Mo₈O₂₆]}_∞ polymer.     

Synthesis,crystal structure and magnetic properties of a new tri‐nuclear iron (II,III) complex,a precursor for the preparation of superparamagnetic Fe3O4 nanoparticles applicable in the removal of Cd2+

This study reports the structural and spectroscopic characterization of a novel metal organic compound formulated as [Fe (bpy)₃] [Fe (dipic)₂]₂.7H₂O ( 1 ) (dipic = pyridine‐2,6‐dicarboxylate and bpy = 2,2^′‐bipyridine). 1 was investigated by elemental analysis, FT‐IR spectroscopy, powder X‐ray diffraction and single crystal X‐ray diffraction (SC‐XRD), which revealed a triclinic structure of expected composition. Thermal degradation of 1 was also investigated. Complex 1 was used as a precursor to prepare superparamagnetic nanoparticles of Fe₃O₄ by thermal analysis. The obtained Fe₃O₄ was characterized by Fourier transformed infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Fe₃O₄ nanoparticles were used as a nano‐adsorbent to remove Cd²⁺ from water at room temperature. The results showed that this nano‐adsorbent is effective in removing Cd²⁺ from contaminated water sources, and that the maximal effectivity of adsorption occurs at pH = 6. Magnetic measurements of complex 1 and Fe₃O₄ nanoparticles at room temperature revealed paramagnetic and superparamagnetic behavior, respectively.     

High‐pressure synthesis and crystal structure of the strontium tungstate Sr3W2O9

The strontium tungstate compound Sr₃W₂O₉ was prepared by a high‐pressure synthesis technique. The crystal structure was determined by single‐crystal X‐ray diffraction and transmission electron microscopy. The structure was found to be a hettotype structure of the high‐pressure phase of Ba₃W₂O₉, which has corner‐sharing octahedra with a trigonal symmetry. Sr₃W₂O₉ has a monoclinic unit cell of C2/c symmetry. One characteristic of the structure is the breaking of the threefold rotation symmetry existing in the high‐pressure phase of Ba₃W₂O₉. The substitution of Sr at the Ba site results in a significant shortening of the interlayer distances of the [AO₃] layers (A = Ba, Sr) and causes a distortion in the crystal structure. In Sr₃W₂O₉, there is an off‐centre displacement of W⁶⁺ ions in the WO₆ octahedra. Such a displacement is also observed in the high‐pressure phase of Ba₃W₂O₉.     

An α‐{P2W18O62}6–‐Based Supramolecular Hybrid Inorganic‐Organic Compound with Visible Light‐Driven Photocatalytic Properties

The α‐[P₂W₁₈O₆₂]^6–‐based coordination polymer [Cu₂(phen)₃(H₂O)₃(P₂W₁₈O₆₂)][Cu(phen)₂(H₂O)] · 5H₂O ( 1 ) (phen = phenanthroline), was hydrothermally synthesized and characterized by single‐crystal and powder X‐ray diffraction, IR and UV/Vis diffuse reflection spectroscopy, and elemental analysis. Structural studies reveal that compound 1 exhibits a three‐dimensional (3D) supramolecular structure based on π–π and hydrogen bonding interactions. In addition, visible light driven photocatalytic experiments of compound 1 were also studied.     

Unexpected Luminescence Properties of Sr0.25Ba0.75Si2O2N2:Eu2+—A Narrow Blue Emitting Oxonitridosilicate with Cation Ordering

Owing to a parity allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition, powders of the nominal composition Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ (2 mol % Eu²⁺) show surprising intense blue emission (λ_em=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr_1?xBa_xSi₂O₂N₂:Eu²⁺, the described compound is a promising phosphor material for pc‐LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X‐ray diffraction methods was used to determine the crystal structure of Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺. HRTEM images reveal the intergrowth of nanodomains with SrSi₂O₂N₂ and BaSi₂O₂N₂‐type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi₂O₂N₂‐type domains was refined on single‐crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON₃‐tetrahedra in pure BaSi₂O₂N₂, in Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.     

High‐Pressure Synthesis and Physical Properties of the Europium‐Substituted Barium Clathrate Ba8−xEuxGe43□3 (x ≤ 0.6)

The new clathrate Ba_8–xEuxGe₄₃□₃ (x = 0.6) was synthesized at a pressure of 1 GPa and temperatures of up to 1220 K by means of a multi‐anvil device (Walker module) and a hydraulic 1000 ton press. X‐ray powder diffraction data indicate that the crystal structure of Ba_8–xEuxGe₄₃□₃ (x = 0.6, space group , a = 21.2588(3) Å) corresponds to that of Ba₈Ge₄₃□₃. Measurements of the magnetic susceptibility of Ba_8–xEuxGe₄₃□₃ reveal Curie‐paramagnetic behaviour and prove that the electronic state of europium corresponds to 4f⁷, i.e., Eu²⁺. Electrical resistivity shows a metal‐like temperature dependence and ρ(300) ≈ 2mΩ cm for x = 0.6. Heat capacity measurements reveal an upturn of c_p/T(T) below 7 K that is attributed to magnetic interaction of the europium ions.     

Organic-inorganic Hybrid Materials Based on Molybdophosphate and Organic Polyammonium

A new organic-inorganic hybrid compound （dienHs）2（P2Mo5O23） （1） [dien=NH（CH2CH2NH2）2] has been hydrothermally synthesized and characterized by elemental analyses, IR spectrum, thermogravimetric analysis, and the single crystal X-ray diffraction technique. Compound 1 crystallizes in the triclinic system with space group P1 and a=0.9790（2） nm, b=0.9922（2） nm, c= 1.4644（3） nm, α=95.510（10）°, β=98.860（10）°, γ=95.700（10）°, V=1.3895（5） nm^3, Z=2, R=0.0465. The results show that the compound consists of dienH3^3＋＋ and P2Mo5O23^6-, and the heteropoly anion P2Mo5O23^6- is connected to a 1-D chain structure with the protonated dien by hydrogen bonds.     

Study of Sb‐doped SnO2 Gray Ceramic Pigment with Cassiterite Structure

In this study, Sb_xSn_1?xO₂ (0 ≤ x ≤ 0.5) compositions were synthesized by the ceramic method from Sb₂O₃‐SnO₂ and Sb₂O₅‐SnO₂ mixtures and characterized by Differential thermal analysis (DTA) and thermogravimetric analysis (TG), X‐ray diffraction, UV‐V‐NIR spectroscopy and CIE L*a*b* (Commission Internationale de l'Eclairage L*a*b*) parameters measurements. Solid solutions with cassiterite structure were obtained at 1300 °C. These solid solutions are stable into glazes. From Sb₂O₃, light gray coloured materials were obtained. From Sb₂O₅, bluish gray coloured materials were obtained at 1300 °C/6h when x ≥ 0.3. Sb_xSn_1?xO₂ with 0.3 ≤ x < 0.5, T = 1300 °C and Sb₂O₅ might be established as compositional range, fired temperature and antimony precursor to obtain gray ceramic pigments in this system.     

One—dimensional Anion—chain Containing [Mo2O6（pic）2]^2—Unit Connected by Unclassical Hydrogen Bond

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Structural Variations in the Solid‐Solution Series LnxCa2−xAl[Al1+xSi1−xO7] with 0 ≤ x ≤ 1 and Ln = La,Eu, Er

Gehlenite, Ca₂Al[AlSiO₇], has melilite‐type structure with space group . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al³⁺, whereas the other one contains Al³⁺ and Si⁴⁺. Normally, the Al³⁺ molar fraction in the second tetrahedrally coordinated position does not exceed x_Al = 0.5, i.e. the so‐called Loewenstein‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La_xCa_2?xAl[Al_1+xSi_1?xO₇], Eu_xCa_2?xAl[Al_1+xSi_1?xO₇] and Er_xCa_2?xAl[Al_1+xSi_1?xO₇] are discussed. All members of the solid solution except the end‐members violate Loewenstein's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group , without changes in the Wyckoff‐positions of the ions compared to gehlenite.