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The optical properties of Yb3+ and Tm3+ co-doped Y2BaZnO5, synthesized by solid-state reaction, are investigated in detail. Three main emission bands centered around 479 nm (blue), 654 nm (red), and 796 nm (near-infrared) are observed under near-infrared laser excitation via an upconversion process. Detailed studies of the upconversion properties as a function of dopant concentrations are described and upconversion efficiencies quantified precisely. Maximum efficiencies of ∼ 1.53% in the 730-870 nm near-infrared emission range and of ∼ 0.09% in the 420-530 nm blue range are obtained. The results of power dependence studies and concentration dependent lifetime measurements are presented. This in-depth spectroscopic study allows us, for the first time, to identify the dominant processes involved in the upconversion mechanism of Yb3+, Tm3+ co-doped Y2BaZnO5 oxides. [ABSTRACT FROM AUTHOR]

Time-of-flight neutron powder diffraction and specific heat measurements were used to study the nature of thermal expansion in rhenium trioxide, an electrically conducting oxide with cubic symmetry. The temperature evolution of the lattice parameters shows that ReO3 can exhibit negative thermal expansion below room temperature and that the transition from negative to positive thermal expansion depends on sample preparation; the single crystal sample demonstrated the highest transition temperature, 294(19) K, and largest negative value for the coefficient of thermal expansion, α=-10(1)×10-7 K-1. For the oxygen atoms, the atomic displacement parameters are strongly anisotropic even at 15 K, indicative of a large contribution of static disorder to the displacement parameters. Further inspection of the temperature evolution of the oxygen displacement parameters for different samples reveals that the static disorder contribution is greater for the samples with diminished negative thermal expansion (NTE) behavior. In addition, specific heat measurements show that ReO3 lacks the low energy Einstein-type modes seen in other NTE oxides such as ZrW2O8. The thermal expansion behavior in other NTE materials such as ZrW2O8, cuprite-type oxides, and the Prussian blue cyanides are discussed and compared with that of our ReO3 samples. [ABSTRACT FROM AUTHOR]

The synthesis of new phases and crystal structures of 11 alkaline earth tartrates, including an unusual [I.sup.3][O.sup.0] framework [Ba(D,L-Tar)] (Tar = [C.sub.4][H.sub.4][O.sub.6.sup.2-]), with 3-D inorganic connectivity is described. The results have shown that the calcium and strontium meso phases are the most thermodynamically stable phases in their systems over a wide temperature range.

The application of nanoindentation and atomic force microscopy to establish the fundamental relationships between mechanical properties and chemical bonding in a dense inorganic-organic framework material, Ce([C.sub.2][O.sub.4])(HC[O.sub.2]) is reported. The study provides insight into vast opportunity to design the mechanical properties of dense hybrid framework materials through the incorporation of organic multifunctional ligands of varying rigidity.

Multiferroic behavior in perovskite-related metal-organic frameworks of general formula [[(C[H.sub.3]).sub.2]N[H.sub.2]M[(HCOO).sub.3], where M = Mn, Fe, Co, and Ni, is described. These compounds have displayed paraelectric-antiferroelectric phase transition behavior in the temperature range 160-185 K, which is associated with an order-disorder transition involving the hydrogen bonded dimethylammonium cations.

Time-of-flight neutron powder diffraction and specific heat measurements were employed to study the nature of thermal expansion in rhenium trioxide, an electrically conducting oxide with cubic symmetry. The temperature evolution of the lattice parameters indicated that Re[O.sub.3] could exhibit negative thermal expansion below room temperature and that the transition from negative to positive thermal expansion depended on sample preparation.

Tc[Br.sub.3] and Tc[Br.sub.4] are prepared by reaction between Tc metal and elemental bromine and characterized by using single crystal XRD. The Tc[Br.sub.3] has displayed the Ti[I.sub.3] structure type, the Tc[Br.sub.4] is isomorphous with Tc[Cl.sub.4] and the bromides of technetium are unique and do not match the behavior of Re.

The synthesis of four organic-inorganic frameworks of alkaline earth cations with the organic ligand 2,5-thiazolo[5,4-d]thiazoledicarboxylate is described. The resulting frameworks have shown how increasing the cation size and coordination requirements have led to greater inorganic connectivity in this system.

An order-disorder type electrical ordering is described at 156 K in [[(C[H.sub.3]).sub.2]N[H.sub.2]]Zn[(HCOO).sub.3]. A hybrid system with the perovskite architecture is described that has displayed a ferroic transition between paraelectric and antiferroelectric states.

The modification of the hydrolysis reaction into a protolysis reaction by using inorganic acids instead of water is examined. The studies have shown that with every ammonium halide used as a protolysis agent, [C.sub.3][H.sub.4] and the respective magnesium halide are obtained as the byproducts, which can be converted to magnesium metal by electrolytic routes.

The complete structure of Tc[O.sub.2] obtained from Rietveld refinement with neutron powder diffraction data is presented.

The synthesis and structure of three compounds based on the M(II)/1,2-ethylenediphosphonic acid system and one based the M(II)/1, 10-phenanthroline/1,2-ethylenediphosphonic acid system (where M = Co, Ni, Mn) are described. The asymmetric unit the complex shows that the [M.sup.2.plus] is six-coordinate with a distorted [M.sup.II][O.sup.5]([H.sub.2]O] octahedron and the phosphonate group (bonded to the [M.sup.2+) is fully deprotonated and that all of the oxygens o the phosphonate group are involved in [M.sup.2+] -O bonds.

Study is conducted to show that a porous hybrid inorganic/organic material, Na[Ni.sub.3](OH)[(SIP).sub.2] [SIP=5-sulfoisophthalate] (1) strongly binds molecular hydrogen at coordinatively unsaturated metal sites. A combination of [H.sub.2] sorption isotherms, temperature programmed desorption, and inelastic neutron scattering spectroscopy show the existence of a significant number of such strong binding sites in (1) along with other sites where hydrogen is more weakly physisorbed.

A three-dimensional iron(III) diphosphonate, Fe(super III)(H2O)(HO3P(CH2)2PO3) is synthesized hydrothermally and characterized by single-crystal X-ray diffraction. The structure consists of inorganic sheets pillared by the 1,2-ethylenediphosphonate groups.