The luminescence properties of colloidal YVO4:Eu nanoparticles (8 nm in diameter) are investigated and compared to those of the bulk materials. The emission quantum yield of nanoparticles is improved after the transfer of the colloidal particles into D2O, showing that surface OH groups act as efficient quenchers of the Eu3+ emission. The growth of a silicate shell around the nanoparticles decreases the optimum europium concentration, showing that energy transfers within the nanoparticles are limited by the quenching of the excited states of the vanadate groups. Nanoparticles also exhibit structural distortions directly related to the small size of the particles. No clear evidence is found concerning the influence of these distortions on the energy-transfer processes, since the improvement of the emission properties observed after thermal annealing of both crude and silicated powders seems to result mainly from the elimination of Eu3+ and vanadate quenchers from the surface. This latter effect is greatly enhanced in the presence of the silicate shell compared to bare particles.

The compounds studied in this work are sol-gel-derived organic-inorganic hybrid materials in which the two components are covalently linked via Si-C bonds. The organic part is a chromophore group derived from dipicolinic acid that is functionalized with trialkoxysilyl groups; the as-obtained silylated monomers are afterward submitted to complexation with rare-earth ions (Eu 3+ , Gd 3+ ) and are used as the siloxane network precursors. The preparation of hybrid materials including covalent grafting and the sol-gel process is described, as well as their luminescence properties. Modifications of the ligand structure (mono-or disubstituted amides) lead to different coordinating properties and to variable absorption edges. As a result, the absorption efficiency or the ability of the chelates to transfer the absorbed energy to Ln 3+ and consequently the quantum yield of the emission are changed. The major effect of silica is a broadening of the emission peaks, whereas spectral repartitions and lifetimes are mainly unchanged as compared with the corresponding organic molecules.

Methods of making mesostructured sol-gel silicate thin films containing two different molecules deliberately placed in two different spatially separated regions in a one-step, one-pot preparation are developed and demonstrated. When the structure-directing agent is the surfactant cetyltrimethylammonium bromide, the structure is 2-D hexagonal with lattice spacings between 31.6 and 42.1 angstroms depending on the dopant molecules and their concentrations. The three general strategies that are used to place the molecules are philicity (like dissolves like), bonding, and bifunctionality. These strategies take advantage of the different chemical and physical properties of the regions of the films. These regions are the inorganic silicate framework, the hydrophobic organic interior of the micelles, and the ionic interface between them. Luminescent molecules that possess the physical and chemical properties appropriate for the desired strategies are chosen. Lanthanide and ruthenium complexes with condensable trialkoxysilane groups are incorporated into the silicate framework. 1,4-Naphthoquinone, pyrene, rhodamine 6G and coumarin 540A, and lanthanides with no condensable trialkoxysilanes occupy the hydrophobic core of micelles by virtue of their hydrophobicity. The locations of the molecules are determined by luminescence spectroscopy and by luminescence lifetime measurements. In all cases, the long-range order templated into the thin film is verified by X-ray diffraction. The simultaneous placement of two molecules in the structured film and the maintenance of long-range order require a delicate balance among film preparation methodology, design of the molecules to be incorporated in specific regions, and concentrations of all of the species.

No abstract

No abstract

No abstract

No abstract

No abstract