Cláudia A. Kodaira

Luminescence Investigations on Eu(III) Thenoyltrifluoroacetonate Complexes with Amide Ligands

The influence of amide ligands on the photoluminescent behavior of tris(thenoyltrifluoroacetonate)- europium(III) in the solid state is reported. Elemental analysis showed that these compounds have the following formulas [Eu(TTA)3·(ANL)2] and [Eu(TTA)3·PZA], where ANL = acetanilide and PZA = pyrazinamide. The photoluminescence spectra of the complexes recorded in the range 420-720 nm at 77 K show narrow bands arising from the 5D0 → 7F J transitions (where J = 0-4), under excitation at 394 nm. Based on the emission spectra and luminescence decay curves the intensity parameters (Ωλ), lifetime (τ) and emission quantum efficiency (η) were determined. The Ω2 values indicate that the Eu3+ion in these complexes is in a highly polarizable chemical environment. The higher value of η (60%) obtained for the complex with the ANL ligand, in comparison with the complex with the PZA ligand (30%), indicates a more efficient deactivation of the Eu3+ion in the [Eu(TTA)3·PZA] complex.

Photoluminescence behavior of the Sm3+ and Tb3+ ions doped into the Gd2(WO4)3 matrix prepared by the Pechini and ceramic methods

The Gd2(WO4)3:RE3+ compounds (where RE3+ = Sm and Tb) were prepared by the Pechini and ceramic methods and characterized by X-ray diffraction and infrared spectroscopy. These rare earth materials present high orange (Sm3+-compound) and green (Tb3+-compound) luminescence intensity under UV radiation. The excitation spectra of these compounds presented broad bands arising from ligand-to-metal charge transfer (O®W and O®RE3+) and narrow bands from 4f-intraconfigurational transitions. The excitation spectra of Tb3+ system also exhibit broad bands attributed to the interconfigurational transition (4f-5d). The emission spectra exhibited the 4G5/2®6HJ (J = 5/2, 7/2, 9/2 and 11/2) and 5D4® 7FJ (J = 0-6) transitions (direct excitation), for the systems doped with Sm3+ and Tb3+, respectively, while a broad band assigned to the LMCT (O®W) is observed when the excitation is monitored on the O®W LMCT state around 270 nm. The experimental intensity parameters hSm and hEu present similar behaviors, suggesting that the Sm3+ ion is in a highly polarizable chemical environment with similar covalent character of the metal-donor atom interaction to the tungstate doped europium system. The cross-relaxation process from the 5D3 to the 5D4 levels of the Gd2(WO4)3:Tb3+ system has been also reported.

Luminescent material based on the [Eu(TTA)3(H2O)2] complex incorporated into modified silica particles for biological applications.

Amino-functionalized luminescent silica particles were investigated for use in immunoassays. The particles were prepared by the Stöber method where the [Eu(TTA)3(H2O)2] complex (TTA: 3-thenoyltrifluoroacetonate) was incorporated into silica particles during the hydrolysis and condensation of TEOS: tetraethylorthosilicate. Then, the amino groups were introduced in the particle surface using APTS: 3-aminopropyltriethoxisilane. The resulting particles were characterized by scanning electron microscopy (SEM), X ray diffraction (XRD) and photoluminescence spectroscopy. In order to demonstrate the viability of the use of luminescent particles as optical markers, an enzyme-substrate reaction was performed using HRP: horseradish peroxidase. It was possible to verify the binding of HRP-oxidized LDL (low density lipoprotein) and anti-oxLDL antibody-luminescent silica particles through the evaluation of the presence of HRP. The bioassay data open a broad field for the development of protein-tagged luminescent particles for use in biomedical sciences.