An unusual way to luminescent terbium molecular-level hybrid materials: Modified methyl benzoic acid covalently bonded w
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The syntheses of modified ortho or meta methylbenzoic acid by (3-aminopropyl)triethoxysilane and the preparation of their corresponding organic–inorganic molecular-based hybrid material with the two components equipped with covalent bonds are described. The organic part is a derivative of methyl benzoic acid, which is used to coordinate to Tb3+ and further introduced into silica matrices by Si–O bonds after hydrolysis and polycondensation processes. The Judd–Ofelt theory proves that covalency increases along with increasing reciprocal energy difference between the 4fN and 4fN−15d1 configurations. Ultraviolet absorption, phosphorescence spectra, and luminescence spectra were applied to characterize the photophysical properties of the obtained hybrid material, and the above spectroscopic data reveal that the triplet energy of modified methyl benzoic acid matches with the emissive energy level of Tb3+. In this way, the intramolecular energy transfer process took place within these molecular-based hybrids, and strong green emission of Tb3+ was obtained.
I. INTRODUCTION
Recently, much research on organic–inorganic hybrid materials has been strongly focused on their extraordinary properties in widespread applications as they combine the advantages of both organic and inorganic networks.1,2 Among the myriad ways the sol-gel approach, which is based on hydrolysis/polycondensation reactions of metal alkoxides, exhibits its unique features are convenience, low temperature, and versatility. In particular, the microstructure, the external shape, or the degree of combination between the two phases can be controlled by changing the sol-gel reaction conditions.3–7 With regard to the resulting hybrids, lanthanide organic complexes introduced in silica gel have already been found to show superior emission intensities to those of simple metal ions in inorganic hosts. Organic components are considered to be efficient sensitizers for the luminescence of rare-earth ions; in short, the antenna effect. Embedding lanthanide complexes with aromatic carboxylic acids, -diketones, or heterocyclic ligands in a sol-gelderived matrix has been discussed in many of the most recent studies.8–13 However, with a conventional doping
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0084 592
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 3, Mar 2005 Downloaded: 17 Mar 2015
method, solving the problem of clustering of luminescent centers seems difficult because only weak interactions (such as hydrogen bonding, van der Waals force, or weak static effect) function between organic and inorganic parts.14 In addition, inhomogeneous dispersion of two phases and leaching of the photoactive molecules frequently occur in this sort of hybrid materials for which the concentration of complexes is also prohibited. As a result, a few studies in terms of the covalently bonded hybrids have appeared, and the as-derived molecularbased materials exhibit monophasic appearance even at a high concentration of rar
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