DYNAMIC PROCESS OF VALENCE CHANGE OF EUROPIUM ION IN EUROPIUM DIFLUORIDE AT HIGH-TEMPERATURE

The dynamic process of the ionic valence changing from Eu~(2+) to Eu~(3+) in EuF_2 at high temperature has been investigated by ESCA, high,temperature X-ray diffraction, high temperature spectrum, high temperature magnetic Isusceptibility and Mssbauer spectrum. It has been shown that the formed Eu~(3+) exists in different compounds when EuF_2 is heated to high temperature in different atmospheres. In air, Eu~(3+) exists in the form of hexagonal EuOF, in nitrogen, in the form of orthogonal EuF_3 and non-hexa...

New dimeric supramolecular structure of mixed (phthalocyaninato)(porphyrinato)-europium(III) sandwiches : preparation and spectroscopic characteristics

The mixed double-decker Eu\[Pc(15C5)4](TPP) (1) was obtained by base-catalysed tetramerisation of 4,5-dicyanobenzo-15-crown-5 using the half-sandwich complex Eu(TPP)(acac) (acac = acetylacetonate), generated in situ, as the template. For comparative studies, the mixed triple-decker complexes Eu2\[Pc(15C5)4](TPP)2 (2) and Eu2\[Pc(15C5)4]2(TPP) (3) were also synthesised by the raise-by-one-story method. These mixed ring sandwich complexes were characterised by various spectroscopic methods. Up to four one-electron oxidations and two one-electron reductions were revealed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). As shown by electronic absorption and infrared spectroscopy, supramolecular dimers (SM1 and SM3) were formed from the corresponding double-decker 1 and triple-decker 3 in the presence of potassium ions in MeOH/CHCl3.

Peptide-lanthanide interactions. Crystal structure of a europium(III)-triglycine complex

Crystals of Eu-(Gly-Gly-Gly).(H2O)5.(ClO4)3 are triclinic, spacegroup P1BAR with a = 9.123 (2), b = 11.185 (5), c = 11.426 (2) angstrom; alpha = 90.79 (2), beta = 98.08 (1), gamma = 98.57 (2)-degrees; Z = 2. The europium cation is surrounded by four oxygens from three different peptide units and four oxygens from water molecules. The geometry around the metal is a distorted bi-capped trigonal prism. The peptide backbone conformation in this complex is compared with those in the free peptide and in various metal complexes. Considerable differences are observed between Eu(III) and Ca(II) complexes of triglycine. (C) Munksgaard 1994.

A self-assembled, luminescent europium cholate hydrogel: a novel approach towards lanthanide sensitization

We propose a new self-assembly based strategy for the design of novel lanthanide based luminescent materials. In this approach a europium hydrogel is prepared and sensitization is achieved by doping the gel with pyrene in a non-coordinated fashion.

Metastable phase relations and europium(II) luminescence of barium hexa-aluminates prepared by gel to crystallite conversion

Wet chemical reaction of hydrated alumina gels, Al2O3.yH(2)O(80

High-Performance Metal-Insulator-Metal Capacitors Using Europium Oxide as Dielectric

We report the first demonstration of metal-insulator-metal (MIM) capacitors with Eu2O3 dielectric for analog and DRAM applications. The influence of different anneal conditions on the electrical characteristics of the fabricated MIM capacitors is studied. FG anneal results in high capacitance density (7 fF/mu m(2)), whereas oxygen anneal results in low quadratic voltage coefficient of capacitance (VCC) (194 ppm/V-2 at 100 kHz), and argon anneal results in low leakage current density (3.2 x 10(-8) A/cm(2) at -1 V). We correlate these electrical results with the surface chemical states of the films through X-ray photoelectron spectroscopy measurements. In particular, FG anneal and argon anneal result in sub-oxides, which modulate the electrical properties.

Structure-mechanical property correlations in mechanochromic luminescent crystals of boron difluoride dibenzoylmethane derivatives

The structure and mechanical properties of crystalline materials of three boron difluoride dibenzoylmethane (BF(2)dbm) derivatives were investigated to examine the correlation, if any, among mechanochromic luminescence (ML) behaviour, solid-state structure, and the mechanical behaviour of single crystals. Qualitative mechanical deformation tests show that the crystals of BF(2)dbm(Bu-t)(2) can be bent permanently, whereas those of BF(2)dbm(OMe)(2) exhibit an inhomogeneous shearing mode of deformation, and finally BF(2)dbmOMe crystals are brittle. Quantitative mechanical analysis by nanoindentation on the major facets of the crystals shows that BF(2)dbm(Bu-t)(2) is soft and compliant with low values of elastic modulus, E, and hardness, H, confirming its superior suceptibility for plastic deformation, which is attributed to the presence of a multitude of slip systems in the crystal structure. In contrast, both BF(2)dbm(OMe)(2) and BF(2)dbmOMe are considerably stiffer and harder with comparable E and H, which are rationalized through analysis of the structural attributes such as the intermolecular interactions, slip systems and their relative orientation with respect to the indentation direction. As expected from the qualitative mechanical behaviour, prominent ML was observed in BF(2)dbm(Bu-t)(2), whereas BF(2)dbm(OMe)(2) exhibits only a moderate ML and BF(2)dbmOMe shows no detectable ML, all examined under identical conditions. These results confirm that the extent of ML in crystalline organic solid-state fluorophore materials can be correlated positively with the extent of plasticity (low recovery). In turn, they offer opportunities to design new and improved efficient ML materials using crystal engineering principles.

Investigations on valence-change behaviors of europium ions in Eu-doped aluminate and silicate phosphors

Compounds of Sr3Al2O6: Eu, Sr4Al14O25: Eu, and BaZnSiO4: Eu were synthesized by high-temperature solid state reactions. The doping Eu3+ ions were partially reduced to Eu2+ in Sr4Al14O25: Eu and BaZnSiO4: Eu prepared in an oxidizing atmosphere, N-2 + O-2. However, such an abnormal reduction process could not be performed in Sr3Al2O6: Eu, which was also prepared in an atmosphere of N-2 + O-2. Moreover, even though Sr3Al2O6: Eu was synthesized in a reducing condition CO, only part of the Eu3+ ions was reduced to Eu2+. The existence of trivalent and divalent europium ions was confirmed by photoluminescent spectra. The different valence-change behaviors of europium ions in the hosts were attributed to the difference in host crystal structures. The higher the crystal structure stiffness, the easier the reduction process from Eu3+ to Eu2+.

Europium-directed self-assembly of a luminescent supramolecular gel from a tripodal terpyridine-based ligand.

Eu(III), the last piece in the puzzle: Europium-induced self-assembly of ligands having a C(3)-symmetrical benzene-1,3,5-tricarboxamide core results in the formation of luminescent gels. Supramolecular polymers are formed through hydrogen bonding between the ligands. The polymers are then brought together into the gel assembly through the coordination of terpyridine ends by Eu(III) ions (blue dashed arrow: distance between two ligands in the strand direction).

Synthesis and optical properties of europium-doped ZnS: Long-lasting phosphorescence from aligned nanowires

Quasi-aligned Eu2+-doped wurtzite ZnS nanowires on Au-coated Si wafers have been successfully synthesized by a vapor deposition method under a weakly reducing atmosphere. Compared with the undoped counterpart, incorporation of the dopant gives a modulated composition and crystal structure, which leads to a preferred growth of the nanowires along the [0110] direction and a high density of defects in the nanowire hosts. The ion doping causes intense fluorescence and persistent phosphorescence in ZnS nanowires. The dopant Eu2+ ions form an isoelectronic acceptor level and yield a high density of bound excitions, which contribute to the appearance of the radiative recombination emission of the bound excitons and resonant Raman scattering at higher pumping intensity. Co-dopant Cl- ions can serve not only as donors, producing a donor-acceptor pair transition with the Eu2+ acceptor level, but can also form trap levels together with other defects, capture the photoionization electrons of Eu2+, and yield long-lasting (about 4 min), green phosphorescence. With decreasing synthesis time, the existence of more surface states in the nanowires forms a higher density of trap centers and changes the crystal-field strength around Eu2+. As a result, not only have an enhanced Eu2+ -4f(6)5d(1)-4f(7) intra-ion transition and a prolonged afterglow time been more effectively observed (by decreasing the nanowires' diameters), but also the Eu2+ related emissions are shifted to shorter wavelengths.

Solvent extraction of americium and europium ions by amide-derivatized polyethers from picric acid aqueous solution

The extraction of Am3+ and Eu3+ from picric acid aqueous solution by N,N-1,2-ethanediyl-bis[2-(N,N-diphenyl-carbamoyl-methoxy)-benzamide] was investigated by a radioactive tracer technique. The composition of the extracted species has been determined as ML(Pic)(3) (M = Eu, Am). The effect of various parameters such as pH, organic diluents, different extractants, picric acid concentration and extractants concentration on the extraction of Am3+ and Eu3+ has been studied. The extraction equilibrium mechanism has been also evaluated and discussed.

Europium complexes immobilization on titania via chemical modification of titanium alkoxide

We report a facile strategy to tether lanthanide complexes to organic-inorganic hybrid titania materials via sol-gel processing by employing chemically modified titanium alkoxide as the precursor where the organic ligand sensitizing the luminescence of lanthanide ions is bonded to titanium.