abstract
Organic-inorganic hybrids incorporating Tb(acac)(3)center dot 3H(2)O (where acac is acetylacetonate) were synthesized via conventional hydrolysis sol-gel reaction in the presence and absence of an acid catalyst (hydrochloric acid, HCl). The host framework of these materials, named di-ureasils, is formed by polyether-based chains grafted to both ends to a siliceous backbone through urea cross-linkages (-NHC(C = O)NH-). Four different concentrations of HCl (0.5, 1.0, 1.5, and 2.0 mol L-1) were used as catalyst for hydrolysis reactions. The gelation time of the resulting materials depends on the HCl concentration varying between 5 and 20 min. The hybrids were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Si-29 and C-13 magic-angle spin nuclear magnetic resonance (NMR) and photoluminescence spectroscopy. The emission quantum yield for the undoped hybrids lies between 8.7 and 10.6%, much higher than those obtained for analogous samples prepared via conventional hydrolysis in the absence of catalyst. For the Tb3+-containing hybrids the lanthanide local environment was affected due to different synthetic conditions used. An increase in the D-5(4) lifetime values, relatively to that of the isolated Tb(acac)3 center dot 3H(2)O complex, is in good agreement with a smaller D-5(4) non-radiative transition probability in the hybrids suggesting the replacement of the Tb3+ coordinated water molecules by the oxygen atom of the carbonyl group of the di-ureasil host. (c) 2008 Elsevier B.V. All rights reserved.
keywords
BETA-DIKETONATE COMPLEXES; SOL-GEL GLASS; ENERGY-TRANSFER; QUANTUM YIELDS; EU3+-BETA-DIKETONATE COMPLEX; ORGANIC/INORGANIC HYBRIDS; SPECTROSCOPIC PROPERTIES; LUMINESCENT PROPERTIES; MOLECULAR DESIGN; LIGHT-EMISSION
subject category
Chemistry
authors
Lima, PP; Ferreira, RAS; Junior, SA; Malta, OL; Carlos, LD
our authors
Luís Carlos
Full professor
Maria Rute de Amorim e Sá Ferreira André
Full professor
Patrícia Pereira Lima
Post-doc Fellowshipacknowledgements
This work was Supported by Funda ao para a Ciencia e Tecnologia (SFRH/BPD/34365/2006), CAPES and CNPq (Brazilian agencies) and the RENAMI project (Brazilian Molecular and Interfaces Nanotechnology Network). The authors Would liketothank Dr.Veronica Zea Bermudez (UTAD, Portugal) and Prof.JoAo Rocha (University of Aveiro, Portugal) for their help on the infrared spectra and on the 29Si/13C NMR measurements, respectively.