Daniel Zambon

Molecular design of luminescent organic-inorganic hybrid materials activated by europium (III) ions

Abstract Luminescent hybrid materials consisting in rare-earth (Eu 3+ , Gd 3+ ) organic complexes covalently attached to a silica-based network have been obtained by a sol–gel process. Four dicarboxylic acids with different aromatic subunits (dipicolinic acid, 4-phenyl-2,6-pyridinedicarboxylic acid, 4-(phenylethynyl)-2,6-pyridinedicarboxylic acid and 2,6-Bis(3-carboxy-1-pyrazolyl)pyridine) have been chosen as ligands for Ln 3+ ions. They were grafted to 3-aminopropyltriethoxysilane (APTES) to give organically modified alkoxysilanes that were used as molecular precursors for the preparation of hybrid materials. Ln 3+ first coordination sphere, composition of the siloxane matrix and connection between the organic and inorganic parts have been characterized by infrared spectroscopy, by 13 C 29 Si solid-state NMR as well as by elemental analyses. UV excitation in the organic component resulted in strong emission from Eu 3+ ions due to an efficient ligand-to-metal energy transfer. As compared to reference organic molecules, hybrid samples exhibited similar emission properties under UV excitation in addition to mainly unchanged excited states lifetimes. However, by direct excitation of the Eu 3+ - 5 D 0 energy level, the presence of two different site distributions were evidenced in the four hybrid compounds. Emission features related to each of these site distributions and their respective attribution were investigated. Variations in the relative emission intensities were observed according to the nature of the organic chromophore. These variations were discussed in relation to the ATE (Absorption-Transfer-Emission) mechanism and to the relative energy positions of the ligand and the rare-earth ions respectively.

Luminescence of the orthoborate YBO3:Eu3+. Relationship with crystal structure

Abstract Pseudo-vaterite structure of YBO3 has been determined from X-Ray data taken from a single crystal. This orthoborate crystallizes in the P6 3 m space group. The structure exhibits two types of [YO8] polyhedra due to the existence of two environments for the yttrium ions. The Eu3+ luminescence in this compound corroborates fairly well the structural determination by identification of two crystallographic sites both showing a C3 symmetry.

Synthesis and optical features of an europium organic–inorganic silicate hybrid

Abstract An europium organic–inorganic silicate hybrid was synthesized by grafting a coordinative group (dipicolinic acid) to a silicate network precursor (3-aminopropyltriethoxysilane) via a covalent bonding. Sol–gel process and complexation were performed using different experimental conditions. The hybrid materials, in particular the Eu 3+ coordination mode, were characterized by infrared and luminescence spectroscopies. Morphology of the materials and TG analysis showed that grafted silica enhanced thermal and mechanical resistances of the organic part.

Spectroscopic properties of trivalent gadolinium in diphosphate CsYP2O7

The mechanism of energy transfer in the diphosphate CsY1−xGdxP2O7 (0 < x ≤ 1) has been studied both at room and at liquid nitrogen temperatures. Decay curves of the emission arising from the 6P7/2 state of Gd3+ were analyzed in the entire concentration range. The experimental curves have been fitted with the Yokota and Tanimoto model, assuming a diffusion-limited process. The derived diffusion constant and interaction parameters suggest a temperature dependence of this process.

Luminescence of Gd3+ activated LiNaY2F8

Abstract The luminescence of Gd 3+ in LiNaY 2 F 8 is reported. The confirmation of the crystal structure is deduced from the emission and excitation spectra recorded at room temperature. It is shown that the Gd 3+ ions are randomly distributed over the two sites of the Y 3+ ions. Sets of crystal field parameters are proposed and the various lines are assigned to each site.

Synthesis and structural characterization of new defect pyrochlore type AxLnySb2O6+z antimoniates (0 < x, y, z < 1; A = Rb, Cs, Tl; Ln = Eu, Gd, and Y) prepared by coprecipitation

New cubic defect pyrochlore type A{sub x}Ln{sub y}Sb{sub 2}O{sub 6+z} antimoniates (0<x,y,z<1; A=Rb, Cs, Tl; Ln=Eu, Gd, and Y) (space group Fd3m) were prepared by calcination in air at 650 deg. C of compositions obtained by a coprecipitation method. Their crystal structures were refined by the Rietveld procedure and further confirmed by X-ray absorption spectroscopy (EXAFS) experiments. Refinements of the X-ray powder diffraction data show a partial and statistical occupation of the 8b site by alkaline or thallous ions and oxygen and lead to values close to 0.33 for the only refinable positional x parameter of the 48f oxygenated site.

Luminescence–structure correlation in CaYOBO3:Eu3+

Abstract The spectroscopic properties of europium calcium orthoborate are investigated under site-selective laser excitation in the 5 D 0 → 7 F 0 region. Results show that at least two site distributions are present. Careful analysis of the principal transitions 5 D 0 → 7 F 0–2 shows disagreement with the local symmetry description of the sites over which the europium ions are distributed.

The type IV polymorph of KEu(PO3)4

Single crystals of KEu(PO3)4, potassium europium(III) polyphosphate, were obtained by solid-state reactions. This monoclinic form is the second polymorph described for this composition and belongs to type IV of long-chain polyphosphates with general formula A I B III(PO3)4. It is isotypic with its KEr(PO3)4 and KDy(PO3)4 homologues. The crystal structure is built of infinite helical chains of corner-sharing PO4 tetrahedra with a repeating unit of eight tetrahedra. These chains are further linked by isolated EuO8 square antiprisms, forming a three-dimensional framework. The K+ ions are located in pseudo-hexagonal channels running along [01] and are surrounded by nine O atoms in a distorted environment.

Three zinc(II) and cadmium(II) complexes containing 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole and polynitrile ligands: synthesis, molecular and supramolecular structures, and photoluminescence properties

Three photoluminescent complexes containing either ZnII or CdII have been synthesized and their structures determined. Bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ2N1,N5]bis(dicyanamido-κN1)zinc(II), [Zn(C12H10N6)2(C2N3)2], (I), bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ2N1,N5]bis(dicyanamido-κN1)cadmium(II), [Cd(C12H10N6)2(C2N3)2], (II), and bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-κ2N1,N5]bis(tricyanomethanido-κN1)cadmium(II), [Cd(C12H10N6)2(C4N3)2], (III), all crystallize in the space group P-1, with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor CdII complexes (II) and (III) are isomorphous. A combination of N-H...N and C-H...N hydrogen bonds and π-π stacking interactions generates three-dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)-(III) indicate that the energies of the π-π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.

Sodium terbium(III) polyphosphate

Single crystals of the title compound, NaTb(PO3)4, were obtained by solid-state reaction. This compound belongs to type II of long-chain polyphosphates with the general formula A I B III(PO3)4. It is isotypic with the NaNd(PO3)4 and NaEr(PO3)4 homologues. The crystal structure is built up of infinite crenelated chains of corner-sharing PO4 tetrahedra with a repeating unit of four tetrahedra. These chains, extending parallel to [100], are linked by isolated TbO8 square antiprisms, forming a three-dimensional framework. The Na+ ions are located in channels running along [010] and are surrounded by six oxygen atoms in a distorted octahedral environment within a cut-off distance <2.9 Å.