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Uranyl complex dissolved in room-temperature ionic liquids has diagnostic absorption and emission spectra that has allowed the identification of the symmetry and geometry of the complex. The uranyl complexes are examined in imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids.

The complex formation of uranyl UO(sub 2)(super 2+) with chloride ions in acetonitrile is studied by UV-vis and U L(sub III) EXAFS spectroscopy. The investigations point to the existence of a [UO(sub 2)Cl(sub 4)](super 2-) species in solution with D(sub 4h) symmetry.

The synthesis and characterization of near-infrared (NIR) emitting complexes of Nd(III), Er(III) and Yd(III) based on hexacoordinate lanthanide ions with an aryl functionalized imidodiphosphinate ligand, tpip, are described. The results indicate the effective shielding of the lanthanide by the twelve phenyl groups of the tpip ligands and the reduction of high-energy vibrations in close proximity to the lanthanide, which are the two important features in the design of NIR emitting lanthanide complexes.

The complex formation of the uranyl ion with chloride ions in acetonitrile is examined by factor analysis of ultraviolet-visible absorption and U [L.sub.3] edge EXAFS (extended X-ray absorption fine structure) spectra. The U(VI) coordination of the solution species [U[O.sub.2][Cl.sub.2]([H.sub.2]O)[(MeCN).sub.2]] has changed during the crystallization of replacing one MeCN molecule with a bridging [[mu].sub.3].O atom in the tetramer.

The unique absorption properties of the 9-hydroxyphenalen-1-one (HPHN) ligand are explored to obtain visible-light-sensitizable rare-earth complexes in 1:3 and 1:4 metal-to-ligand ratios. The X-ray crystal structures of the tris complexes have shown solvent coordination to the central rare-earth ion, whereas in the tetrakis complexes, the four [PHN.sup.-] ligands form a protective shield around the central ion, preventing small solvent molecules from coordinating to the rare-earth ion, at least in the solid state.

A rare case of low-percentage trivalent lanthanide doping in multinuclear lanthanide polyoxometalates (LnPOMs) was investigated. The [La 4 (MoO 4 )(H 2 O) 16 (Mo 7 O 24 ) 4 ] 14- polyanion was chosen as the host material for this study. In this polyanion the central [La 4 (MoO 4 )] 10+ core is coordinated by four heptamolybdate groups as well as 16 water molecules. The tetranuclear lanthanum POM was doped with 5% of Eu 3+ , Tb 3+ , Sm 3+ , Dy 3+ , Nd 3+ , Er 3+ , and Yb 3+ (according to synthesis), and the structures and luminescence properties of the x%Ln:LaPOMs were investigated. Additionally a series of tetranuclear lanthanide POMs built from [Mo 7 O 24 ] 6- heptamolybdate polyanions with Eu 3+ , Tb 3+ , Sm 3+ , Dy 3+ , and Nd 3+ instead of La 3+ were synthesized, and a detailed analysis revealed that the tetranuclear clusters formed monomers or dimers linked through oxygen bridges. The smaller lanthanide ions, namely, Er 3+ and Yb 3+ , did not form tetranuclear clusters, but instead mononuclear sandwich-type POMs were obtained. The obtained structures were shown to be lanthanide-specific, and not a result of different synthetic/crystallization conditions. The luminescence properties of the x%Ln:LaPOMs were compared with the luminescence properties of the LnPOMs.

Microstructures of Y2WO6 were prepared by applying a hydrothermal synthesis in the presence of sodium dodecyl sulfate (SDS) surfactant, after which the materials were heat-treated at a temperature of 1100 °C. When prepared at pH 3, the spherical 3D microstructures were built from nanosized particles. Raising the pH gave materials built from differently shaped building blocks, which influenced the final architecture. These materials, similarly to other previously investigated and reported rare-earth tungstate materials, were found to show very interesting luminescence properties. However, quantum yield (QY) values have scarcely been reported for such materials. In this work, a detailed study of the photoluminescence characteristics, decay times, and quantum yields of Y2WO6 doped with Sm(3+), Eu(3+), and Dy(3+) is presented. When doped with different concentrations of Ln(3+) ions, the luminescence properties of the samples changed. The 2.5% Dy:Y2WO6 sample gave white-light emission and showed a QY of 17%. For the optimal lanthanide-ion concentrations, the systems were codoped with 2% and 10% Gd(3+) ions to test the possible enhancement of luminescence through energy transfer from W-O and/or Gd(3+) to Ln(3+). The Eu(3+),Gd(3+)-codoped system showed QYs as high as 79%. The Sm,Gd-codoped system showed the highest enhancement of QY. After incorporation of Gd(3+) ions, the 2.5% Sm_10% Gd:Y2WO6 materials showed a QY approximately 2.4 times larger than that of the 2.5% Sm:Y 2WO6 material.