No abstract

Novel oxygen sensors consisting of a [Ru(bpy)2phen]2+ (bpy: 2,2′‐bipyridyl, phen: phenathroline) portion covalently grafted to a mesostructured silica‐based network are prepared in situ via a sol–gel approach with the help of cetyltrimethylammoniumbromide (CTAB) surfactant. 1,10‐Phenanthroline covalently grafted to 3‐(triethoxysilyl)propyl isocyanate is used as not only the sol–gel precursor but also as the second ligand of the Ru(bpy)2Cl2 · 2H2O complex to prepare the sol–gel‐derived mesostructured silicates for an oxygen sensor. For comparison purposes, the oxygen sensors in which [Ru(bpy)2phen]Cl2 is conventionally physically incorporated into the matrix are also prepared. Elemental analysis, NMR, Fourier transform IR, UV‐vis electronic absorption, luminescence‐intensity quenching Stern–Volmer plots, and excited‐state decay analysis are used to characterize the obtained oxygen sensors. These obtained bulk xerogels and spin‐coated thin films show that the homogeneity and the sensitivity of the covalently grafted samples are superior to those of the physically incorporated ones, and the highest sensitivity is obtained in the mesostructured bulk xerogel. This improvement in oxygen sensitivity is attributed to the increased diffusivity of oxygen in the uniform and nearly parallel porous structure of the Mobil Catalytic Material 41 mesostructured matrix, the enhanced homogeneity results from the covalently grafted propyl group in –Si–(CH2)3– that acts as the fundamental spacer which prevents interaction between the attached RuII complex and the silica matrix, and optimal dispersion in the mesopores during the sol–gel polycondensation. Furthermore, the greatly minimized leaching effect of the sensing molecules could be observed in the covalently grafted system. The covalent grafting strategy presented in this paper provides superior optical oxygen sensors with homogeneous distribution, improved sensitivity, and simplified calibration plots.

Pure hexagonal-phased Y 1-x BO 3 :Eu x (x ) 0-0.30) nanocrystals with different particle sizes were prepared by a facile sol-gel pyrolysis process, and their photoluminescence spectra evidently showed a size-dependent characteristic because the ratio of the red emission transition ( 5 D 0 f 7 F 2 ) to the orange emission transition ( 5 D 0 f 7 F 1 ) (R/O) was much higher in the smaller particles. Both XRD patterns and IR spectra demonstrated that the lattices of YBO 3 :Eu nanocrystals were distorted and that as the particle size became smaller, the lattices became more distorted. Studies on the charge transfer (CT) bands indicated that Eu 3+ ions can be excited preferentially by different excitation sources in both the bulk and the nanocrystals, suggesting that at least two different types of intrinsic luminescent sites, site 1 and site 2, coexist in YBO 3 :Eu. Site-selective excitation spectra also revealed that a particular site, site 3, existed concurrently in the nanocrystals. Site 2, the site with relatively inferior symmetry of the intrinsic sites, was identified to be of C 1 symmetry. Meanwhile, for the nanosized samples, Eu 3+ ions exhibited enhanced R/O values in both sites 2 and 3, which might be ascribed to the distorted lattices, and thus displayed the observed superior color chromaticity. A pronounced energy transfer between site 2 and site 3 in the nanocrystals was also observed while Eu 3+ concentration was increased to the quenching concentration, which indicated that site 3 may be a disordered surface site surrounding the interior sites.

The momentum and helicity density distributions of the strange quark sea in the nucleon are obtained in leading order from charged-kaon production in deep-inelastic scattering on the deuteron. The distributions are extracted from spin-averaged K� multiplicities, and from K� and inclusive double-spin asymmetries for scattering of polarized positrons by a polarized deuterium target. The shape of the momentum distribution is softer than that of the average of the and quarks. In the region of measurement 0.021.0�GeV2, the helicity distribution is zero within experimental uncertainties