Stokes and Anti-Stokes Luminescent Rare-Earth-Doped Tantalum Oxide Nanoparticles.

Doping of nano- and microparticles of oxides with rare earth elements (REEs) is used to fine-tune their structural, optical, and electrochemical properties. On the way to establish the structure-property relationship, we dope tantalum oxide (Ta2O5) particles with REEs to study their effect on the oxide structure and luminescence. Ta2O5 is highly perspective in medicine, catalysis, and optics, but its crystal structure is insufficiently studied. Two synthesis approaches (sol-gel and solvothermal) were used to obtain powders with different textures. Experimental and theoretical studies of amorphous and crystallized tantalum oxide NPs by means of X-ray powder diffraction, Rietveld analysis, EXAFS/XANES spectroscopy, and density functional theory calculations were performed. All samples (doped and undoped) crystallized in orthorhombic phase with no admixtures. It was demonstrated that Ta2O5 is a promising wide-spectrum luminescent material: by combining REEs, both Stokes and anti-Stokes luminescence in the visible region were obtained. By means of optical absorption spectroscopy, it was shown that the prepared samples could be classified as wide band gap semiconductors.

Annealing-Induced Structural Behavior of Mn Dopant Ions in Calcium Orthovanadate Ca3(VO4)2 Single Crystals.

The crystal and local structures of Czochralski-grown calcium orthovanadate (Ca3(VO4)2) single crystals doped with over-stoichiometric 0.05 wt % Mn2O3 (CVO:0.05Mn) and annealed under different conditions are studied by single-crystal conventional and synchrotron X-ray diffraction, X-ray absorption spectroscopy, and electron paramagnetic resonance for the first time. Bottom (annealing in air) and top (annealing in air and in vacuum) parts of the CVO:0.05Mn crystal differ in the manganese content (higher in the bottom part), formal charge (Mn4+ and Mn(3+δ)+, respectively), and color (orange bottom part; light orange and yellow top parts annealed in air and vacuum, respectively). Manganese ions are located in one (Ca3, distorted two-capped trigonal prism) of five crystallographic Ca sites and have octahedral coordination, which is consistent with crystal-chemical properties of transition-metal ions. The presence of vacancies in one of three V sites is revealed. Formal charge 5+ for vanadium ions is confirmed by X-ray photoelectron spectroscopy. Different colors of CVO:Mn crystals and different formal charges of manganese are explained depending on the growth and post-growth treatment conditions.

Revealing the peculiar local behavior of manganese and cobalt in diffusion-doped calcium orthovanadate Ca3(VO4)2.

Laser Ca3(VO4)2 single crystals (СVO; space group R3c, Z = 21) with crystallochemical formula Ca118Ca218Ca318Ca46(Ca5 + Са5А)3(V118V218V36)O168 grown by the Czochralski method were doped with Мn2O3 (CVO:Мn2O3) and Сo3O4 (CVO:Co3O4) by high-temperature diffusion annealing. Statistical and local structures were comprehensively studied by single-crystal and powder synchrotron X-ray diffraction and conventional single-crystal X-ray diffraction as well as by X-ray absorption spectroscopy for the first time. The presence of Mn(2+δ)+ ions with a mixed formal charge and Co2+ ions in the Ca2 (monocapped trigonal prism), Ca3 (two-capped trigonal prism), and Ca4 (octahedron) sites was revealed by diffraction methods. The tetrahedral coordination and the coordination intermediate between tetrahedral and octahedral were established for Mn(2+δ)+ and Co2+ ions, respectively. A fundamentally different structural behavior of dopant ions (concentration, formal charge, and coordination environment) in the CVO crystals doped with manganese in the form of Mn2O3 during the crystal growth or by high-temperature diffusion annealing was observed. The relationship between characteristic bands in the absorption, fluorescence, and excitation spectra of CVO:Мn2O3 and CVO:Co3O4 samples and transition metals with specific formal charges is discussed.

Mechanism of Zr Incorporation in the Course of Hydrothermal Synthesis of Zeolite BEA.

The mechanism of Zr-BEA hydrothermal synthesis in fluoride media has been investigated through the detailed characterization of samples obtained at different synthesis times by XRD, XRF, TGA, multinuclear solid-state NMR, FTIR, SEM, TEM with EDS, XAS, and nitrogen sorption. The synthetic procedure involved hydrothermal crystallization of the gel with the following composition: 1SiO2:0.54TEAOH:0.54HF:0.005ZrO2:5.6H2O. The formation of open and closed Lewis acid sites was monitored by FTIR spectroscopy of adsorbed CO, while coordination of Zr was studied by XAS. The results show that the formation of Zr-BEA proceeds by two steps. In the first step, pure silica BEA is crystallized via a solid-solid hydrogel rearrangement mechanism. Zirconium species are occluded in Si-BEA crystals in the form of Zr-rich silicate particles. These particles do not provide for any appreciable Lewis acidity. In the second step, Zr incorporation into T positions of the zeolite structure takes place, leading to the formation of closed Zr sites, which are partially converted into open sites at longer synthesis times. It is demonstrated that the content of open and closed sites can be tuned by variation of the synthesis time.

Heterometallic Palladium(II)-Indium(III) and -Gallium(III) Acetate-Bridged Complexes: Synthesis, Structure, and Catalytic Performance in Homogeneous Alkyne and Alkene Hydrogenation.

The reaction of Pd3(OOCMe)6 with indium(III) and gallium(III) acetates was studied to prepare new PdII-based heterometallic carboxylate complexes with group 13 metals. The heterometallic palladium(II)-indium(III) acetate-bridged complexes Pd(OOCMe)4In(OOCMe) (1) and Pd(OOCMe)4In(OOCMe)·MeCOOH (1a) were synthesized and structurally characterized with X-ray crystallography and extended X-ray absorption fine structure in the solid state and solution. A similar Pd-Ga heterometallic complex formed by the reaction of Pd3(OOCMe)6 with gallium(III) acetate in a dilute acetic acid solution, as evidenced by atmospheric pressure chemical ionization mass and UV-vis spectrometry, was unstable at higher concentrations and in the solid state. Complex 1 catalyzes the liquid-phase-selective phenylacetylene and styrene hydrogenation (1 atm of H2 at 20 °C) in acetic acid, ethyl acetate, and N, N-dimethylformamide solutions, while no Pd metal was formed until alkyne and alkene hydrogenation ceased.