Abstract
A series of complexes of europium (III)/gadolinium (III) with 2-thienyltrifluoroacetonate (HTTA), terephthalic acid (TPA) and phenanthroline (Phen) were synthesized by coprecipitation. The resulting complexes including Eu2(TPA)(TTA)4Phen2, Eu1.4Gd0.6(TPA)(TTA)4Phen2, Eu1.0Gd1.0(TPA)(TTA)4Phen2 and Eu0.8Gd1.2(TPA)(TTA)4Phen2 were characterized by elemental analysis, IR spectroscopy and thermal stability analysis. The results of analysis indicate that the complexes obtained have similar binuclear structure with each other. The thermal stability analysis indicates that the complexes Eu2(TPA)(TTA)4Phen2and Eu1.0Gd1.0(TPA)(TTA)4Phen2 possess good thermal stability, which melt at ~241°C and decompose at ~370°C - 430°C corresponding to the formation of the complexes. The fluorescence spectra of Eu2(1-x)Gd2x(TPA)(TTA)4Phen2 (x = 0 - 1) complex powders and their doped silica gels were studied. The co-fluorescence effect of Gd3+ ions in complex powders is different from that of their doped silica gels. The optimum concentration of Gd3+ for complex powders and their doped silica gels is 0.5 and 0.3 (molar fraction), respectively. The co-fluorescence distinction of Gd3+ ions for complex powders and their doped silica gels is preferably interpreted from the proposed binuclear structure together with monomolecular compositions of the complexes for the first time. Both intermolecular energy transfer and intra molecular energy transfer in cross binuclear monomolecular EuGd(TPA)(TTA)4Phen2 are thought to be responsible for the co-fluorescence effect of the complex powders; yet only the latter is thought to be responsible for the co-fluorescence effect in silica gels, for the complex molecules in this case are isolated from each other.
Highlights
The fluorescence enhancement of the trivalent rare earth complexes still enjoys a growing interest due to their important application in time-resolved fluoroimmunoassays, electro-optical devices and amorphous luminescent materials [1]-[4]
The separations (∆ = υas − υs) between υas peaks and υs pears are in the range of 155 - 159 cm−1 in the Eu (III) complexes, which are attributed to the bidentate chelating, bidentate bridging and tridentate chelating-bridging coordination modes of carboxylate groups with rare earth ions, since the separations (∆ = υas − υs) in the Eu (III) complexes are lower than that in Na2TPA (Δ = 168 cm−1) [19] [20]
To investigate the co-fluorescence effect of Gd3+ for the complex powders and their doped silica gels, We would assume that co-fluorescence Gd3+ ions have no influence on the fluorescence intensity of Eu3+ in the complexes, the relative emission intensity value Icalc of the complex powders and their doped silica gels was calculated according to the molar fraction of Eu3+ in different co-fluorescence complexes, and the Iexp is the relative emission intensity value for experiment, so the ratios of Iexp and Icalc can be gotten
Summary
The fluorescence enhancement of the trivalent rare earth complexes still enjoys a growing interest due to their important application in time-resolved fluoroimmunoassays, electro-optical devices and amorphous luminescent materials [1]-[4]. The fluorescence of rare earth complexes can be further enhanced by the use of synergistic agents, such as trioctylphosphine oxide, phenanthroline, organic phosphates and sulphoxides. In the presence of these ions, the fluorescence enhancement of some rare earth complexes can be obtained This process is referred to as co-fluorescence, which is extensively studied in the mononuclear complexes of Europiun (III) ions with β-diketones ligands, such as Eu(TTA)3Phen [12], Eu(Dbm)3Phen [13] and Eu(TTA)3TPPO2. Synthesis and fluorescent properties of the mononuclear complexes of europium (III) with β-diketones ligands (e.g. 2-thienyltrifluoroacetonate (HTTA), dibenzoylmethide) and Phenanthroline (Phen) or trioctylphosphine oxide have been shown [12] [13] [18]. IR absorption spectra and thermal stability of the above mentioned complexes were studied
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