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For the first time, the Sr2La8 – xTmx(GeO4)6O2 (x = 0.1–1.0) solid solution with the apatite structure were synthesized by the solid-phase method, and their spectral–luminescence properties were studied. The prospects of using these compounds as phosphors in the visible and short-wave infrared ranges were demonstrated. The luminescence of Sr2La8 – xTmx(GeO4)6O2 germanates, which occurs under ultraviolet radiation, is characterized by the high purity of blue color; the chromaticity coordinates are close to commercially available phosphors. The Sr2La8 – xTmx(GeO4)6O2 compounds efficiently convert 808 nm laser radiation into a series of emission lines in the 1.3–2.2 μm spectral range, caused by sequential 3H4 → 3F4 and 3F4 → 3H6 transitions in Tm3+ ions. Germanate Sr2La7.6Tm0.4(GeO4)6O2 with a maximum emission intensity in the short-wave infrared region shows high thermal stability of luminescence in the 30–220°C range.

Cubic garnets activated by neodymium and holmium, Li6CaLa2Nb2O12:Nd3+,Ho3+, were obtained by solid-state method. The main regularities of changes in the luminescence properties of Li6C-aLa2Nb2O12:Nd3+,Ho3+ solid solutions in the visible, near-IR, and short-wave IR ranges under 808 nm laser diode radiation are determined. The energy transfer mechanism between active centers, involving the participation of Nd3+ ions as sensitizers for the luminescence of Ho3+ ions, is proposed. Low phonon energy, high luminescence intensity in the range of 2.0–3.0 μm, and weak up-conversion luminescence in the region of 450–780 nm make it possible to consider the cubic lithium–lanthanum niobates Li6CaLa2Nb2O12:Nd3+,Ho3+ as promising phosphors of the short-wave IR range.

Cyclogermanate Sr3La2(Ge3O9)2, isostructural to silicate Sr3Er2(Si3O9)2, activated by neodymium and holmium is obtained for the first time by the precursor method. Ion Nd3+ in the structure of Sr3La2(Ge3O9)2 is a sensitizer of the infrared luminescence of Ho3+. Excitation by radiation with a wavelength of 808 nm leads to a series of emission lines in the luminescence spectra of Sr3La2-xNd x (Ge3O9)2 : Ho3+ in the short-wave and middle-IR ranges (1.0–3.4 μm). The highest intensity of lines at 2.1 and 2.7 μm, associated with the 5I7 → 5I8 and 5I6 → 5I7 transitions in the Ho3+ ion, is found for compositions containing traces of holmium. Based on the analysis of the concentration dependences of the luminescence intensity, an optimal composition of the phosphor is determined, which ensures the maximum efficiency of conversion of laser radiation energy. The data obtained are interpreted in the assumption of cross-relaxation energy transfer from Nd3+ to Ho3+.

Solid solutions CaLa2-xEu x Ge3O10 (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa2Ge3O10, they crystallize in the monoclinic system, space group P21/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa2Ge3O10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established.

Solid solutions CaLa2–xNdxGe3O10:Ho3+, Er3+ have been synthesized, their optical characteristics have been studied, and the dependences of the Stokes luminescence in the 0.9–3.0 µm region on the concentration of neodymium ions under 808 nm laser diode excitation have been determined. Based on analysis of the obtained dependences, the optimal composition of the phosphor with the maximum efficiency of the energy conversion is established.

The crystal structure and luminescence properties of CaY2Ge3O10:Ln3+ (Ln = Eu, Tb) germanates synthesized via a conventional solid-state reaction and an ethylenediaminetetraacetic acid complexing process are studied. The CaY2 − xLnxGe3O10 (Ln = Eu, Tb; x = 0–1.0, 2.0; Δx = 0.1) solid solutions have a monoclinic structure (space group P21/c, Z = 4), in which dopant ions occupy three nonequivalent noncentrosymmetric sites with different Ca2+/Ln3+ ratios. The effect of the synthesis methods, dopant concentrations, and excitation wavelengths on the luminescence properties of the compounds obtained is determined.

The vanadium(V) complexes K[VO2(SeO4)(H2O)] and K[VO2(SeO4)(H2O)2] · H2O were synthesized using original procedures; their physicochemical properties were studied, and the crystal structure was determined on the basis of X-ray diffraction and neutron diffraction data. The structure of K[VO2(SeO4)(H2O)2] · H2O is composed of VO6 octahedra connected to form infinite chains by bridging SeO4 tetrahedra. Each VO6 tetrahedron has short terminal V-O bonds forming the bent dioxovanadium group VO2+ The unit cell parameters of K[VO2(SeO4)(H2O)2] · H2O are a = 6.4045(1) A, b = 9.9721(2) A, c = 6.6104(1) A, β = 107.183(1)°, V = 403.34 A3, Z = 2, monoclinic system, space group P21. The complex K[VO2(SeO4)(H2O)] forms a two-dimensional layered structure composed of highly distorted VO6 octahedra having two short terminal V-O bonds and SeO4 groups coordinated simultaneously by three vanadium atoms. This compound crystallizes in the monoclinic system (space group P21/c): a = 7.3783(1) A, b = 10.5550(2) A, c = 10.3460(2) A, β = 131.625(1)°, V = 602.894(5) A3, Z= 4. The vibrational spectra of the studied compounds are fully consistent with their structural features.

Synthesis was performed and physicochemical properties were studied for the M4V2O3(SO4)4 complexes, where M = K, Rb, or Cs. Their crystal structures were determined using the set of data from X-ray diffraction and neutron diffraction studies. All compounds crystallize in a triclinic lattice (space group \( P\bar 1 \) , Z = 2) with the parameters: a = 7.7688(2), 7.8487(1), 8.1234(1) A; b = 10.4918(3), 10.8750(2), 11.1065(1) A; c = 11.9783(4), 12.1336(2), and 11.8039(1) A; α = 76.600(2)°, 77.910(1)°, 79.589(1)°; β = 75.133(2)°, 75.718(1)°, 87.939(1)°; γ = 71.285(2)°, 72.189(1)°, 75.567(1)°; V = 881.78(5), 945.42(3), 1014.34(2) A3 for K, Rb, Cs, respectively. The structure of M4V2O3(SO4)4 was found to be formed by discrete complex anions V2O3(SO4)44− incorporating two oxygen-bridged vanadium atoms in a distorted octahedral oxygen environment. The sulfate groups are coordinated by the vanadium atoms in the chelating mode with a large scatter of S-O interatomic distances and OSO angles. Every VO6 octahedron has a short terminal vanadium-oxygen bond with a length of about 1.6A. The V2O3(SO4)44− complex anions in potassium and rubidium compounds differ from that in Cs4V2O3(SO4)4 in the type of symmetry and mutual spatial orientation. The vibrational spectra were presented and interpreted in line with the structural analysis data.

By the hydration of MVO(SeO(4))(2) with saturated water vapors at room temperature a series of isostructural complex compounds of vanadium(V) of the composition M[VO(2)(SeO(4))(H(2)O)(2)]center dot ...

Potassium oxosulfatovanadate(V) K3VO2(SO4)2 has been obtained by solid-phase synthesis from K2SO4, K2S2O7, and V2O5 (2: 1: 1), and its formation conditions, crystal structure, and physiochemical properties have been studied. The conversions of K3VO2(SO4)2 in contact with potassium vanadates and other potassium oxosulfatovanadates(V) are considered in terms of phase relations in the K2O-V2O5-SO3 system, which models the active component of vanadium catalysts for sulfur dioxide oxidation into sulfur trioxide. The X-ray diffraction pattern of K3VO2(SO4)2 is indexed in the monoclinic system (space group P21) with unit cell parameters of a = 10.0408(1) A, b = 7.2312(1) A, c = 7.3821(1) A, β = 104.457(1)°, Z = 2, and V = 519.02 A3. The crystal structure of K3VO2(SO4)2 is built from [VO2(SO4)2]3− complex anions, in which the vanadium atom is in an octahedral oxygen environment formed by two terminal oxygen atoms (V-O(6) = 1.605(7) A, V-O(10) = 1.619(7) A and four oxygen atoms of the two chelating sulfate anions. The vibrational spectra of K3VO2(SO4)2 are analyzed using these structural data.

Vanadium(V) complexes of general composition M3VO2(SO4)2 (M = Rb, Cs) were synthesized by a solid-state route. The individuality of the synthesized compounds was proved by X-ray and neutron diffraction, vibrational spectroscopy, and microscopic analysis. The X-ray diffraction patterns of M3VO2(SO4)2 were indexed to fit the monoclinic system (space group P2/c, Z = 4) with the following unit cell parameters: a = 11.6487(2) A, b = 8.4469(2) A, c = 12.1110(2) A, β = 109.483(1)°, V = 1123.43 A3 (Rb); a = 12.0546(3) A b = 8.7706(2) A, c = 12.6496(3) A, β = 109.843(2)°, V = 1257.99 A3 (Cs). In the crystal structure of M3VO2(SO4)2, [VO2(SO4)2]3− complex anions can be discerned in which the vanadium atom is surrounded by five oxygen atoms: two oxygen atoms form short terminal V–O bonds, and three oxygen atoms are from the two sulfato groups, one of which acts as a monodentate ligand and the other acts as a bidentate chelating ligand.

Compounds described as V2O3(XO4)2, where X = S or Se, were prepared from vanadium(V) oxide mixtures with concentrated sulfuric and selenic acids. The physicochemical properties of the products were studied; for V2O3(SeO4)2, the crystal structure was determined by powder X-ray diffraction and neutron diffraction, and its key differences from the structure of V2O3(SO4)2 were identified. V2O3(SeO4)2 crystallizes in the monoclinic system with the unit cell parameters a = 15.3831(2)A, b = 5.54096(5)A, c = 9.71644(7)A, β = 111.886(1)°, V = 768.51A3, space group C2/c (no. 15).

The formation conditions and physicochemical properties of binary decavanadates M4Na2V10O28 · 10H2O (M=K, Rb, NH4), synthesized by crystallization from saturated solutions of the NaVO3-MH2AsO4-H2O systems, were studied by chemical analysis, X-ray powder diffraction, microscopy, thermogravimetry, and IR spectroscopy. To optimize the synthesis conditions of M4Na2V10O28 · 10H2O, the ( 1-x)NaVO3 · 2H2O · xMH2AsO4-H2O (0.2 ≤ x ≤ 0.8) isomolar series method was applied to studying the interaction in the NaVO3-MH2AsO4-H2O systems (M = K, Rb, Cs) at the 0.4 mol/L total molar concentration of NaVO3 and MH2AsO4 in solutions. The studied M4Na2V10O28 · 10H2O compounds were shown to be isostructural with triclinic crystals (Z= 1, space group P\( \bar 1 \)), and their unit cell parameters were estimated.

This paper reports on the results of structural and optical investigations of a new class of layered compounds Ln2Ga(GeO3)4 (Ln = Gd, Ho, Er, Yb, Y), which are promising for the use in photonics as converters of laser radiation.

The crystal structure of dioxovanadium(V) sulfate trihydrates A[VO2(SO4)(H2O)2] · H2O, where A is K, Rb, Tl, or NH4, has been determined based on a combination of neutron and X-ray diffraction data. The compounds are isostructural and have a monoclinic lattice (space group P21, Z = 2) with unit cell parameters a = 6.24535(8), 6.26016(7), 6.25817(5), and 6.2500(1) A; b = 9.8417(1), 9.99736(8), 9.96217(9), and 9.9742(1) A; c = 6.52113(8), 6.69303(5), 6.70379(6), and 6.70334(9) A; β = 106.99(1)°, 107.83(1)°, and 107.83(1)°, 107.99(1)°, respectively. The SO4 tetrahedra and VO4(H2O)2 octahedra share an oxygen vertex to form infinite isolated chains. Atoms A have CN = 10. IR and Raman spectroscopy data are reported.

The crystal structure of alkali-metal dioxovanadium(V) sulfates AVO2SO4, where A is K or Rb, has been determined based on a combination of neutron and X-ray diffraction data. The compounds are isostructural and have an orthorhombic lattice (space group P212121, Z = 4) with unit cell parameters a = 11.1004(2) and 10.8193(1) A; b = 8.2626(2) and 8.9042(1) A; c = 5.4772(1) and 5.5722(1) A, respectively. The structures are of the chain type. Zigzag chains are formed by vertex-sharing VO6 octahedra. Sulfate groups SO4 link neighboring chains and form a spatial framework with cavities accommodating alkali-metal atoms with CN = 9 (K) and 8 (Rb). IR and Raman spectroscopy data are reported.

Complex oxides A 3 M 2 O 8 (A = Sr, Ba; M = P, As, V) with the palmierite structure (space group R -3 m (no. 166), Z = 3) [1‐6] are considered as promising ceramics, ionic conductors, and membrane materials. In the structures of these compounds, the A cations occupy 3 a and 6 c positions with coordination numbers (CN) of 6 and 10, respectively. The M cations occupy 6 c positions (CN = 4) and the O atoms are in 6 c and 18 h positions. The A 3 M 2 O 8 oxides are quite stable with respect to heterovalent replacement in the cationic (A, M) and anionic sublattices; for example, Ba 3 (W,Nb) 2 O 8 , Ba 3 Mo 2 O 6 N 2 , and Ba 3 W 2 O 6 N 2 were obtained [7, 8]. The double orthovanadates A 2 Ln 2/3 (VO 4 ) 2 with the palmierite structure were found in the A 3 (VO 4 ) 2 –LnVO 4 binary systems, where A = Ca, Sr, Ba; Ln = La, Nd [9, 10]. In this group of compounds, 6 c positions are statistically occupied by two sorts of cations, 0.3333 Ln 3+ and 0.5 A, while 3 a positions contain only one sort of cation (A). These compounds can be considered as the limiting compositions of solid solutions formed upon replacement of A atoms in the orthovanadates A 3 (VO 4 ) 2 , where A = Ca, Sr, Ba. Thus, if the valences are balanced, one can expect the formation of stable compounds upon any heterovalent substitution in the sublattices, which may be either complete or defective. However, no data on the A 3 M 2 O 8 oxides with heterovalent substitutions in the 3 a position have been reported. In this work, we report the results of synthesis and study of the structural and electronic properties of a new orthovanadate Sr 2 Bi 2/3 (VO 4 ) 2 in which Sr → Ba heterovalent substitution in the 3 a position is implemented for the first time. The compound was prepared by solid-phase synthesis from special purity grade bismuth and vanadium(V) oxides and strontium carbonate. The reactants were mixed and subjected to stepwise annealing in the temperature range 550–1100°e with a temperature rise by 100°e every 12‐15 h. The samples were pressed into

The phase equilibria in the ternary system La2O3-Nb2O5-Nb have been studied at subsolidus temperatures in vacuum (6.65 × 10−3 Pa), and the temperature stability limits of LaNb7O12 have been determined in vacuum and during heating in air.

The crystal structure of the low-temperature form of K3PO4 has been determined for the first time using neutron diffraction (Rietveld method) and Raman spectroscopy: orthorhombic cell (sp. gr. Pnma, Z = 4), lattice parameters a = 1.12377(2) nm, b = 0.81046(1) nm, c = 0.59227(1) nm. The structure is made up of isolated [PO4] tetrahedra, with the potassium ions in between.

The new compounds CeNb7O12 and PrNb7O12, isostructural with LaNb7O12, have been synthesized and characterized by x-ray diffraction. The structures of the LnNb7O12 (Ln = La, Ce, Pr) compounds have space group P21/c (Z = 4), with lattice parameters a = 10.764(2), 10.743(2), 10.738(4) A; b = 9.192(2), 9.146(2), 9.137(3) A; c = 10.313(2), 10.304(2), 10.303(3) A; and β = 104.25(2)°, 104.31(2)°, and 104.21(3)°, respectively. The reduction in the lattice parameters of LnNb7O12 in going from La to Pr correlates with the ionic radii of Ln: r(La3+) > r(Ce3+) > r(Pr3+). In the Nd(Sm)-Nb-O systems, phases of stoichiometry LnNb7O12 have not been obtained.

The phase compositions of theLaVO4-SrMoO4(1) and Sr2GeO4-SrMoO4 (2) binary systems, which bound the Sr2GeO4-LaVO4-SrMoO4 (3) ternary system, and the LaSr2(VO4)(GeO4)-Sr2GeO4+SrMoO4 section (4) of system 3 are studied at subsolidus temperatures. Systems 1 and 2 consist of a mixture of the initial compounds, and the La1 − xSr2 + x(GeO4)(V1 − xMoxO4) (where 0 ≤ x ≤ 0.4) region of substitutional solid solutions with a palmierite structure is formed in system 3. The unit cell parameters of the solid solutions are determined. The distribution of the lanthanum and strontium cations over two positions of the cationic sublattice is described.

Phase equilibria in the Ba3(VO4)2-K2Ba(MoO4)2 and Pb3(VO4)2-K2Pb(MoO4)2 systems have been investigated. In the first system, a continuous series of substitutional solid solutions with the palmierite structure is formed, and in the second one, the polymorphic transition in lead orthovanadate at 100°C restricts the extent of the palmierite-type solid solution to 10–100 mol % K2Pb(MoO4)2.