Luminescence properties of the ternary rare earth complexes with beta-diketones and 1,10-phenanthroline incorporated in silica matrix by a sol-gel method

Ternary complexes of rare earth Eu(dbm)(3).phen and Tb(acac)(3).phen (dbm = dibenzoylmethanide, acac = acetylacetone and phen = 1,10-phenanthroline) were introduced into silica gel by the sol-gel method. The result indicated that the rare earth ions (EU3+ and Tb3+) showed fewer emission lines and slightly lower emission intensities in the silica gel than in the pure rare earth complexes. The lifetimes of rare earth ions in silica gel (Eu3+ and Tb3+) doped with Eu(dbm)(3).phen and Tb(acac)(3).phen were longer than those in purl Eu(dbm)(3).phen and Tb(acac)(3).phen. A very small amount of rare earth complexes doped in a silica gel matrix can retain excellent luminescence properties. (C) 1997 Elsevier Science S.A.

Luminescence properties of the ternary terbium complexes with (ortho and para) aminobenzoic acids and 1,10-phenanthroline incorporated in silica matrix by a sol-gel method

Ternary complexes of terbium with ortho (and pam) aminobenzoic acid and 1,10-phenanthroline were introduced into silica gel by the sol-gel method. The luminescence behavior of the solid-state samples was studied during the sol-gel aging process by means of emission. excitation spectra, lifetimes and quantum efficiencies.

Sol-gel synthesis and luminescence of Y4Al2O9:RE3+(RE=Eu, Tb)

Y4Al2O9 (YAM) was prepared by a sol-gel process, using yttrium and aluminum citrate complexes as precursors. The sol-gel process produced single-phase YAM at 900 degrees C, as opposed to the conventional solid-state reaction, which led to the formation of other phases, even if at 1600 degrees C. The emission and excitation spectra of Eu3+ and Tb3+ in YAM showed the existence of two luminescence centers, agreeing with the crystal structure of YAM. The spectral properties of the samples are discussed.

COMPARATIVE-STUDY OF CA4Y6(SIO4)(6)O-A PHOSPHORS PREPARED BY SOL-GEL AND DRY METHODS (A=PB2+,EU3+, TB3+,DY3+)

Ca4Y6(SiO4)(6)O:A (A = Pb2+, Eu3+, Tb3+, Dy3+) phosphors have been prepared by two methods: the sol-gel method and the conventional dry method. The crystallization processes and the luminescence characteristics of the phosphors were studied, The sol-gel method features low-temperature formation of the phosphor, leading to successful preparation of Pb2+-activated phosphors which could not be prepared by the dry method at high temperature. The (4f)(8-)(4f)(7)(5d)(1) absorption band of Tb3+ and the charge-transfer (CT) band of Eu3+ have higher energies and narrower half-widths in the sol-gel-derived phosphors than in the phosphors prepared by the dry method, respectively. The Tb3+ and Dy3+ ions show stronger emission in the former than in the latter. Both the yellow-to-blue intensity ratio (Y:B) of Dy3+ and the red-to-orange intensity ratio (R:O) of Eu3+ in the sol-gel-derived phosphors are smaller than those for the phosphors derived by the dry method.

An in-situ modified sol-gel process for monolith catalyst preparation used in the partial oxidation of methane

An in-situ modified sol-gel method for the preparation of a Ni-based monolith-supported catalyst is reported. With the presence of a proper amount of plasticizer and binder, and at an optimized pH value, the stable boehmite sol was modified with metal ions (Ni, Li, La) successfully without distinct growth of the particle size. Monolith-supported Ni-based/gamma-Al2O3 catalysts were obtained using the modified sol as the coating medium with several cycles of dip-coating and calcination. Combined BET, SEM-EDS, XRD and H-2-TPR investigations demonstrated that the derived monolith catalysts had a high specific surface area, a relatively homogeneous surface composition, and a high extent of interaction between the active component and the support. These catalysts showed relatively stable catalytic activities for partial oxidation of methane (POM) to syngas under atmospheric pressure. The monolith catalysts prepared by this sol-gel method also demonstrated an improved resistance to sintering and loss of the active component during the reaction process.

Mesoporous spinel MgAl2O4 prepared by in situ modification of boehmite sol particle surface: I Synthesis and characterization of the unsupported membranes

Mesoporous spinel membranes as ultrafiltration membranes were prepared through a novel sol-gel technique. By in situ modification of the sol particle surface during the sol-gel process, control of the material structure on a nanometer scale from the earliest stages of processing was realized. Nano-particles with a chocolate-nut-like morphology, i.e. spinel MgAl2O4 as a shell and gamma -Al2O3 as a core, were first revealed by HRTEM results. The formation of the spinel phase was confirmed by X-ray diffraction (XRD). N-2 adsorption-desorption results showed that the mesoporous membranes had a narrow pore size distribution. (C) 2001 Elsevier Science B.V. All rights reserved.

Preparation of titania-based catalysts for formaldehyde photocatalytic oxidation from TiCl4 by the sol-gel method

Titania sols were prepared by acid hydrolysis of a TiCl4 precursor instead of titanium alkoxides. The effect of acid concentration on the particle size and stability of sol was investigated. Stable titania sols with mean particle size of 14 nm could be obtained when the H+/Ti molar ratio was 0.5. The titania sols were modified with Pt, SiO2, ZrO2, WO3 and MoO3 to prepare a series of modified catalysts, which were used for the photocatalytic oxidation of formaldehyde at 37 degreesC. They showed different photocatalytic activities due to the influence of the additives. Comparing with pure TiO2, the addition of silica or zirconia increased the photocatalytic activity, while the addition of Pt and MoO3 decreased the activity, and the addition Of WO3 had little effect on the activity. It is of great significance that the conversion of formaldehyde was increased up to 94% over the SiO2-TiO2 catalyst. The increased activity was partly due to higher surface area and porosity or smaller crystallite size. A comparison of our catalyst compositions with the literature in this field suggested that the difference in activity due to the addition of a second metal oxide maybe caused by the surface chemistry of the catalysts, particularly the acidity. (C) 2001 Elsevier Science B.V. All rights reserved.