Red luminescence in MgO-GeO<Subscript>2</Subscript> gel glasses and glass ceramics doped with Mn ions prepared by sol-gel method

To obtain red luminants, MgO-GeO₂ gel glasses and glass ceramics doped with manganese ions were prepared by a sol-gel method and their properties were investigated by measuring X-ray diffraction (XRD), electron spin resonance (ESR), and luminescence and excitation spectra. Under UV irradiation at 254 nm, the gel glasses and glass ceramics showed red luminescence at 620–665 nm, the intensity of which became strong with increasing the heat-treatment temperature. A glass ceramic with the composition 1.0MnO-25MgO-75GeO₂ heat treated at 1000°C exhibited the strongest red luminescence at 661 nm. From the results of XRD and ESR, this luminescence is found to be due to the transition from the ⁴T_1g to the ⁶A_1g state of octahedrally coordinated Mn²⁺ ions located in MgGeO₃ polycrystals. The luminescence wavelength of the glass ceramics (∼665 nm) is long compared with Eu³⁺-containing phosphors (612 nm), therefore the glass ceramics can be expected for red luminants.     

Chemiluminescence in the reaction of LnI<Subscript>2</Subscript> (Ln = Dy,Nd) with water

Chemiluminescence (CL) upon the reaction of crystalline LnI₂ (Ln = Dy, Nd) with water was found. The CL emitters are the Ln³⁺* electron-excited ions (Dy³⁺*, λ_max = 470, 570 nm; Nd³⁺*, λ = 700–1200 nm) generated by the electron transfer from the Ln^II ions to the H₂O molecules. The identified reaction products are H₂, dissolved LnI₃, and insoluble LnI(OH)₂ (49–51% and 48–50% yield for DyI₂ and NdI₂, respectively). The treatment of NdI₂ with an H₂O solution in THF gives the NdI₂OH(thf)₂·3H₂O complex and hydrogen. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1890–1893, October, 2007.     

A Novel Uranyl Complex with Dimeric Lacunary Polyoxoanion: [(A-α-SiW<Subscript>9</Subscript>O<Subscript>33</Subscript>)<Subscript>2</Subscript>K{UO<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)}<Subscript>2</Subscript>]<Superscript>11−</Superscript>

A novel uranyl complex with dimeric lacunary polyoxoanion like open-mouthed clam, Na₅[(A-α-SiW₉O₃₃H₃)₂K{UO₂(H₂O)}₂], was prepared and characterized by elemental analysis, infrared and ultraviolet–visible spectroscopy and single crystal X-ray diffraction. In the anion, two A-α-SiW₉O₃₄¹⁰⁻ groups share two terminal oxygen atoms O_d′ derived from removal of three corner-shared W atoms from saturated α-Keggin anion, forming a dimeric anion with an open mouth in which potassium ion and uranyl ions are coordinated. Uranium atom adopts a pentagonal bipyramidal geometry. The coordinating anions are linked by sodium ions via coordination of terminal or bridging oxygen atoms, forming two-dimensional layer arrangement. Between the layers are the hydrogen bonds from which a supramolecular architecture is created. UV–VIS spectrum gives W–O and U–O charge transfer transitions at 230–265 and 432 nm, showing the change of geometry of the polyanion and weakening of the U–O bonds of the uranyl cation. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users.     

The synthesis and selected properties of Co<Subscript>2</Subscript>InV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been demonstrated that Co₂V₂O₇ and InVO₄ react with each other forming a new compound of the Co₂InV₃O₁₁ formula, when their molar ratio is equal to 1:1, or among CoCO₃, In₂O₃ and V₂O₅, mixed at a molar ratio of 4:1:3. This compound melts incongruently at the temperature of 960±5°C, depositing crystals of InVO₄. It crystallizes in the triclinic system and the unit cell parameters amount to: a=0.6524(6) nm, b=0.6885(5) nm, c=1.0290(4) nm, α=96.5°, β=104.1°, γ=100.9°, Z=2. The phase equilibria being established in the Co₂V₂O₇–InVO₄ system over the whole components concentration range up to the solidus line were described.     

Low temperature synthesis of nanosized ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript> photocatalysts by a citrate complex method

Nanosized ZnNb₂O₆ photocatalysts (band gaps ~4.0 eV) were successfully synthesized via a citrate complex method. Their particle sizes ranged from 50 to 150 nm. The result of Mott–Schottky measurement revealed that the flat-band potential of ZnNb₂O₆ was ca. −1.3 V versus Ag/AgCl at pH 6.6. The photocatalytic activities of the samples for the degradation of methyl orange were evaluated under UV-light (λ = 254 nm). It was found that the sample obtained at 850 °C showed the highest photocatalytic activity due to its opportune crystallinity and surface area. Furthermore, ·OH radicals were detected as the major oxidation agents responsible for the decomposition of methyl orange.     

ESR and luminescence of ZnWO<Subscript>4</Subscript> crystals activated by gadolinium ions

The crystals of zinc tungstate (ZTO) are a radiation-hardened matrix and are widely used as scintillators for high energy radiation. Therefore, it is interesting to study the possibility of introducing gadolinium ions into this structure to obtain the lasing properties. In order to activate ZTO crystals by gadolinium ions, 0.5 mol.% of Gd₂O₃ is added to the load. High-quality large crystals of ZTO are produced. The spectra of optical transmission, luminescence excitation, and luminescence are measured at room temperature. It is shown that the introduction of gadolinium ions does not result in a shift of the main luminescence band of the ZTO crystals. The analysis of the ESR spectra and their modeling enables the calculation of spin-Hamiltonian parameters. It is shown that the observed spectrum depends on the state of Gd³⁺ ions with S = 7/2 and is well described by the spin-Hamiltonian parameters g _x = 1.9835, g _y = 1.9685, g _z = 1.9688 and D = 644.88 Gs, E = 161.49 Gs. Directions of the principal values of the D tensor are determined; they reflect a strong distortion of the nearest-neighbor oxygen environment.     

New metal-rich mixed chalcogenides with an intergrowth structure: Ni<Subscript>5.68</Subscript>SiSe<Subscript>2</Subscript>, Ni<Subscript>5.46</Subscript>GeSe<Subscript>2</Subscript>, and Ni<Subscript>5.42</Subscript>GeTe<Subscript>2</Subscript>

New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni_5.68SiSe₂, Ni_5.46GeSe₂, and Ni_5.42GeTe₂, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M_7−δEX₂-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the intergrowth structure type under consideration are discussed. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Preparation and electrochemical performance of nano-structured Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for supercapacitor

Nano-structured spinel Li₂Mn₄O₉ powder was prepared via a combustion method with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O), and oxalic acid (C₂H₂O₄·2H₂O) as raw materials, followed by calcination of the precursor at 300 °C. The sample was characterized by X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy techniques. Electrochemical performance of the nano-Li₂Mn₄O₉ material was studied using cyclic voltammetry, ac impedance, and galvanostatic charge/discharge methods in 2 mol L⁻¹ LiNO₃ aqueous electrolyte. The results indicated that the nano-Li₂Mn₄O₉ material exhibited excellent electrochemical performance in terms of specific capacity, cycle life, and charge/discharge stability, as evidenced by the charge/discharge results. For example, specific capacitance of the single Li₂Mn₄O₉ electrode reached 407 F g⁻¹ at the scan rates of 5 mV s⁻¹. The capacitor, which is composed of activated carbon negative electrode and Li₂Mn₄O₉ positive electrode, also exhibits an excellent cycling performance in potential range of 0–1.6 V and keeps over 98% of the maximum capacitance even after 4,000 cycles.     

Synthesis and crystal structure of complex of Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript> with N-(3-methyl-pyridin-2-yl)-formimidoyl-(3-methyl-pyridin-2-yl) hydrazone

The reaction of 3,6-di-(3-methyl-pyridin-2-yI)-s-tetrazine (DMPTZ, II) with Ce^III salt [Ce(NO₃)₃ · 6H₂O] generates a new ligand, N-(3-methyl-pyridin-2-yl)-formimidoyl-(3-methyl-pyridin-2-yl) hydrazone (L), and forms a new complex: a mononuclear complex [Ce(L)(NO₃)₂ (H₂O)₃] · NO₃ (III). Crystal data for III: space group P-1, with a = 0.7133(4) nm, b = 1.1139(2) nm, c = 1.4572(3) nm, α= 102.13(2)°, β= 99.81(3)°, γ= 91.10(3)°, Z = 2, V = 1113.6(7) nm³, μ = 2.123 mm⁻¹ and F(000) = 630. L acts as a tri-dentate chelating ligand in III. There are 10 coordination sites around Ce³⁺ of III, which are respectively occupied by seven oxygen atoms (four from two nitrate anions and three from three H₂O molecules) and three nitrogen atoms (all from L). The cerium atom and three chelating nitrogen atoms are coplanar. The mechanism of the metal assisted decomposition is discussed briefly.     

Hexametavanadates M<Stack><Subscript>4</Subscript><Superscript>+</Superscript></Stack>M<Superscript>2+</Superscript>(VO<Subscript>3</Subscript>)<Subscript>6</Subscript>: Thermal stability and luminescent characteristics

Rhombohedral hexametavanadates K₄Sr(VO₃)₆, K₄Ba(VO₃)₆, Rb₄ Ba(VO₃)₆, and Cs₄Ba(VO₃)₆ melt incongruently in the temperature range of 491 to 600°C. Cooling of peritectic melts yields mixtures of compounds typical of M₂⁺O-M²⁺O-V₂O₅ systems, far from equilibrium and depending on the cooling kinetics. The vanadate Cs₄Ba(VO₃)₆ undergoes reversible polymorphic transformation at 360°C. All compounds show broad-band luminescence with a maximum of the luminescence spectrum at 490–590 nm with three types of excitation. The vanadates K₄Sr(VO₃)₆ and Rb₄Ba(VO₃)₆ show the highest luminescence intensity at room temperature. The latter is also most efficient at liquid nitrogen temperatures. The luminescence spectra depend on the excitation of vanadates. Three hypotheses were put forward to interpret this finding. The nature of luminescence is attributed to the relaxation of electronic excitation in [VO₄]³⁻ structural tetrahedra present in the vanadates. The performance characteristics of luminophores were determined. These luminophores may be promising as X-ray luminescent screens, radioluminescence indicators, and light-emitting diode devices.     

Synthesis,structure, and electric properties of oxygen-deficient perovskites Ba<Subscript>3</Subscript>In<Subscript>2</Subscript>ZrO<Subscript>8</Subscript> and Ba<Subscript>4</Subscript>In<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>11</Subscript>

Perovskite phases Ba₃In₂ZrO₈ and Ba₄In₂Zr₂O₁₁ with the nominal concentration of structural oxygen vacancies 1/9 and 1/12, respectively, were synthesized by solid-phase and solution methods. X-ray diffraction showed cubic symmetry of both phases with the unit cell parameter a = 0.4193(2) and 0.4204(3) nm, respectively. The absence of superstructural lines resulted in the conclusion on statistical arrangement of oxygen vacancies. Thermogravimetry and mass spectrometry proved that both phases can reversibly absorb water from gas phase (pH₂O = 2 × 10⁻² atm) with observed correlation between the concentration of oxygen vacancies and amount of absorbed water. The total water amount was up to 0.9 mol per formula unit or, if recalculated for perovskite unit ABO₃, 0.3 and 0.23 mol H₂O, respectively. The temperature curves of coductivity in the atmosphere with various partial water vapor pressures (pH₂O = 3 × 10⁻⁵ and 2 × 10⁻² atm) showed significantly higher conductivity and lower activation energy (0.52 eV) in humid atmosphere due to proton transfer. The proton conductivity is up to 5 × 10⁻⁴ Ohm⁻¹ cm⁻¹ at 300°C for Ba₃In₂ZrO₈ specimen. IR spectrometry showed that protons in the structure exist primarily in OH-groups.     

Growth and properties of MnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Homogeneous MnIn₂S₄ single crystals ∼14 mm in diameter and ∼40 mm long were grown by directional solidification of melt. For these MnIn₂S₄ single crystals, the composition was determined by electron probe microanalysis, structure by X-ray diffraction, and melting temperature by differential thermal analysis. Transmission spectra were studied in these single crystals, in the region of the intrinsic absorption edge within 10–300 K. The transmission spectra were used to determine the bandgap width, and it was plotted as a function of temperature. The thermal expansion of MnIn₂S₄ single crystals was studied dilatometrically in the range 80–700 K, and the thermal expansion coefficient was determined.     

Preparation,Thermal Behaviour,and Crystal Structure of MgAl<Subscript>2</Subscript>F<Subscript>8</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>

Summary.  Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂. Received October 29, 2001. Accepted (revised) December 6, 2001     

New uranyl complex with imidazolidine-2-one [UO<Subscript>2</Subscript>(Imon)<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)](ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Structure and some properties

A complex of uranyl perchlorate with imidazolidine-2-one as the molecular ligand, [UO₂(Imon)₄(H₂O)](ClO₄)₂ (I), was synthesized and structurally characterized by X-ray diffraction analysis. The coordination number of the uranium atom is 7. The nearest environment of the uranyl ion includes four O atoms of the imidazolidine-2-one molecules and one O atom of the water molecule. The perchlorate anions are outer-sphere ligands. The crystals are monoclinic: space group P2₁/c; a = 16.294(3) Å, b = 16.135(3) Å, c = 9.987(2) Å, = 97.69 (3)°, V = 2603.0 (9) ų, (calcd) = 2.117 g/cm³, Z = 4. The IR and luminescence spectra of the complex were recorded.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 919–924.Original Russian Text Copyright © 2004 by Andreev, Antipin, Budantseva, Tuchina, Serezhkina, Fedoseev, Yusov.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Interconversion of stannylium ions in the C<Subscript>4</Subscript>H<Subscript>11</Subscript>Sn<Superscript>+</Superscript> system

B3LYP method with the LANL2DZ basis for tin and aug-cc-pVDZ basis for carbon and hydrogen were used to obtain the equilibrium geometry of the main (with a positive charge on the tin) isomers in the C₄H₁₁Sn⁺ system and the transition states at their interconversion. As in the case of silicon and germanium, the cations of lighter elements of the 14th group, the most stable isomer is shown to be the tertiary ion, however, the energy of its complexes with ethane and propane is higher only by several kJ mol⁻¹. Nevertheless, the formation of these complexes from the tertiary ion requires overcoming a rather high barrier (293 and 272 kJ mol⁻¹, respectively). The barrier for isomerization of the secondary ion in the ethane complex is somewhat lower (222 kJ mol⁻¹), but still is significantly greater than the energy gained at the appearance of the nucleogenic ion. The most probable transformation pathways of the nucleogenic stannylium ions are the formation of complexes with ethylene, which requires overcoming barriers of 130 and 117 kJ mol⁻¹ for the tertiary and secondary ions, respectively.     

Preparation and Characterization of GdTaO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Sol-Gel Luminescence Thin Films

High quality GdTaO₄:Eu³⁺ luminescence films have been successfully prepared through a modified sol-gel process. The films were prepared using inorganic materials as raw materials, and the thermal decomposition and UV assisted technique were introduced to improve the quality of the film and reduce the period for forming the thick film. Results of structural studies by atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the surface was smooth and the structure was monoclinic with the average grain size of about 55 nm. The emission and excitation spectra of the film were investigated. Related to the transition ⁵ D₀ →⁷ F₁ and ⁵ D₀→⁷ F₂ of Eu³⁺ ions, the main luminescence peaks were observed at 591 and 611 nm respectively, and the luminescence peak at 345 nm was detected simultaneously related to the TaO₄³⁻ emission. Transmission spectrum and decay curve of the luminescence are also presented in this paper.     

Structure and real composition of undoped and Cr- and Ni-doped Sr<Subscript>0.61</Subscript>Ba<Subscript>0.39</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> single crystals

Strontium barium niobate crystals with congruent melting composition Sr_0.61Ba_0.39Nb₂O₆ (SBN-61), both nominally pure and doped with Cr³⁺ и Ni³⁺ ions, have been investigated by neutron diffraction. Different strontium and barium contents as well as their different distribution over the Sr1, of Sr2 and Ba2 crystallographic sites of SBN-61 structure, caused by introduction of dopants, have been revealed. Coordination polyhedra of cations have been established based on the analysis of cation–anion internuclear distances together with the calculation of bond-valence sums for cations, which are equal to their formal charge. It was found that the Nb1 and Nb2 atoms are located in distorted octahedra with quadfurcated (the Nb1O₆ polyhedron) or bifurcated (the Nb2O₆ polyhedron) vertices, and the Sr1 atoms are located in a cuboctahedron with bifurcated vertices in the base plane. Different polyhedra have been revealed for the Sr2 and Ba2 atoms: Sr2 atoms are coordinated by 15 oxygen atoms to form a highly distorted five-capped pentagonal prism, whereas Ba2 atoms are located in a highly distorted three-capped trigonal prism with a coordination number 9. Comparison of interatomic and internuclear distances, determined by X-ray and neutron diffraction analyses, respectively, allowed to reveal a highly pronounced shift of electron density in Nb1 and Sr2 polyhedra, responsible for the covalent bond and properties of crystals. Location of Cr³⁺ и Ni³⁺ dopant ions in the SBN-61 structure as well as their formal charges has been discussed.     

Generation of fullerenyl radicals and chemiluminescence in the (C<Subscript>60</Subscript>—R<Subscript>3</Subscript>Al)—O<Subscript>2</Subscript> system

Fullerenyl radicals (FR) RC₆₀ ^· and chemiluminescence (CL) are generated in the presence of O₂ in C₆₀—R₃Al (R = Et, Buⁱ) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R^· radical, which is an intermediate of R₃Al autooxidation, to C₆₀. Mass spectroscopy and HPLC were used to identify Et_nC₆₀H_m (n, m = 1–6), Et_pC₆₀ (p = 2–6), and dimer EtC₆₀C₆₀Et as stable products of FR transformations. As found by ESR, the EtC₆₀ ^· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C₆₀— R₃Al)—O₂ system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O₂, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C₆₀—R₃Al)—O₂ system is much brighter (I _max = 1.86·10⁸ photon s⁻¹ mL⁻¹) than the known background CL (I _max = 6.0·10⁶ photon s⁻¹ mL⁻¹) for the autooxidation of R₃Al and is localized in a longer-wavelength spectral region (λ_max = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter ³CH₃CHO* to the products of FR transformation: R_nC₆₀H_m, R_pC₆₀, and EtC₆₀C₆₀Et. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007.