Sol-gel derived urea cross-linked organically modified silicates. 2. Blue-light emission
authors Carlos, LD; Bermudez, VD; Ferreira, RAS; Marques, L; Assuncao, M
journal CHEMISTRY OF MATERIALS
keywords POROUS SILICON; AMORPHOUS-SILICON; LUMINESCENCE; SPECTROSCOPY; EU3+; ION; PHOTOLUMINESCENCE; COORDINATION; EXCITATION; SCATTERING
abstract The photoluminescence and the local structure of sol-gel derived organic-inorganic hybrids, so-called ureasils, are discussed. Their host matrix is a silica-based network to which different numbers of oxyethylene repeat units-8.5, 15.5, and 40.5 for U(600), U(900), and U(2000), respectively-are covalently grafted by means of urea linkages. The small-angle X-ray scattering (SAXS) results suggest a diphasic structure for the morphology of the hybrids induced by local phase separation between siliceous domains and polymeric regions. The estimated interdomain distances, ranging from 27 Angstrom for U(600) to 59-64 Angstrom for U(2000), indicate that the three ureasils are greatly homogeneous on the SAXS scale. The luminescence spectra show a broad light emission (2.0-4.1 eV) with a blue band at similar to 2.6 eV and a purplish-blue one at similar to 2.8-3.0 eV, clearly distinguished by time-resolved spectroscopy. The energies of these two components are related to the dimension of the backbone inorganic skeleton. The local structure of these amorphous siliceous regions is depicted as a planar structure that combines different proportions of six to eight silica-based chains (blue emission) with three to four organically modified Si-O environments (purplish-blue emission). The calculated coherent diffraction lengths of the siliceous domains for U(600), U(900), and U(2000)-16.6, 16.1, and 20.5 Angstrom, respectively-points to an increase of the overall disorder of the inorganic backbone as the quantity of oxyethylene chains increase from 8.5 to 40.5.
publisher AMER CHEMICAL SOC
issn 0897-4756
year published 1999
volume 11
issue 3
beginning page 581
ending page 588
digital object identifier (doi) 10.1021/cm980373n
web of science category Chemistry, Physical; Materials Science, Multidisciplinary
subject category Chemistry; Materials Science
unique article identifier WOS:000079245400014
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