Anne-Christine Franville

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.

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.

Strategies for Spatially Separating Molecules in Mesostructured Sol-Gel Silicate Films

Three strategies for placing molecules in designated regions of mesostructured thin films made by the sol-gel dip-coating technique are demonstrated. These strategies all involve one-step syntheses where all of the components are present in the sol from which the substrate is pulled. Silicate films templated by ionic surfactants contain three spatially-separated regions: a silicate framework, an organic region formed by the hydrocarbon tails of the surfactants, and an intervening ionic interface formed by the charged surfactant head groups. The first method exploits lipophilic interactions between the molecule and the micelle to place it in the organic region. The second method uses chemical bonding of multiple trialkoxysilane groups in a three dimensional array on the molecule to place it in the silica framework. The third method uses multiple functionality at opposite sides of the molecule to enable it to span two regions. Luminescent molecules are used, and spectroscopy monitors the formation.

Functionalized luminescent YVO4: Ln3+ nanoparticles

The synthesis and the emission properties of colloidal YVO4:Ln nanocrystals (8nm in diameter) are investigated, where Ln = Eu, Nd, Yb, Er. The nanoparticles synthesized here are constituted of a (Y,Ln)VO4 crystalline core and stabilized by a lanthanide-citrate complexing shell. Surface derivatization of the particles can be achieved through the controlled growth of a silicate shell using a functionalized silane, with elimination of the citrate shell. The luminescence of the Eu3+ -doped YVO4 colloids is studied in details and compared to the bulk material. Chemical treatments are achieved in order to explain the observed differences. Improvement of the emission quantum yield after the transfer of the colloidal particles into D2O shows that surface OH groups act as efficient quenchers of the Eu3+ emission. The growth of a silica shell around the particles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate ions. Moreover, site selective excitation spectroscopy seems to prove the coexistence of core sites and surface sites for the europium ions. Finally, colloidal nanoparticles exhibit an emission yield of about 25%, which appears already suitable for some applications.

Luminescence Properties of Rare-Earth Ions in Organic-Inorganic Hybrid Mesostructured Thin Films

This paper describes the preparation of hybrid surfactant-templated thin films functionalized with rare-earth (Eu 3+ and Tb 3+ ) organic complexes. 2-D hexagonally ordered films are obtained by a one-pot synthesis process based on an acid-catalyzed approach. Ln 3+ ions are coordinated to bis-silylated ligands that co-polymerize with TEOS, which enables one to incorporate the fluorescent centers within the silica framework. Luminescent properties of the organic-inorganic mesostructured films are discussed and compared to those of amorphous samples with similar composition.

Influence Of Hybridation With A Silicate Network On The Properties Of An Eu 3+ Complex Derived From Dipicolinic Acid

In this paper, the preparation, the characterization and the optical features of organicinorganic materials incorporating a trivalent europium organic chelate into a silicate network are described. The covalent grafting and the sol-gel process allow to obtain monophasic hybrid gels in which the structure and the activity of the organic molecules were retained. The Eu 3+ coordination mode is not sensitive to the sol-gel processing conditions whereas the morphology of materials, their thermal resistance and their luminescence properties may be adjusted. Characteristics of hybrid compounds are compared to those of the corresponding organic species.