The solid compound YNbO4:Eu3+ was synthesized by an usual solid state reaction and a non-conventional method of thermal decomposition of precursors. X-ray diffraction data of the monoclinic YNbO4 were used to identify the crystalline M-fergusonite phase. The symmetry of the luminescent Eu3+ site is very close to the D2 point symmetry. Spectroscopic quantities, namely, the 5D0-7F0/5D0-7F2 intensity ratio, the 5D0-7F1 transition splitting (DE0-1) and the intensity parameters Wl (l = 2, 4) were obtained from the emission spectrum at 77 K. In this sequence their values are 4.0 10-3, 103 cm-1, 18.0 10-20 cm2 and 3.2 10-20 cm2. Theoretical predictions are discussed in terms of the simple overlap model (SOM). The yttrium niobate structural data were taken as basis to obtain the spherical coordinates of the ligand oxygen atoms. The Eu-O distances being corrected in the frame of rare earth niobate series vs. atomic number. Their predicted values are 3.9 10-3, 85 cm-1, 14.9 10-20 cm2 and 3.0 10-20 cm2, assuming 0.9 as the effective charge of the ligand ions and their polarizabilities relative to the metal-ligand (M-L) distance as follows [R(Å)/ a(Å3)]: 2.443/0.6, 2.427/1.2, 2.370/2.3, 2.349/3.5

Os íons európio e térbio trivalentes possuem raios iônicos semelhantes àquele do Ca 2+ . Em função disto, eles são usados como sondas de sítios de ligação de cálcio em moléculas de seres vivos. Tais íons possuem características espectroscópicas muito úteis ao seu estudo, particularmente uma luminescência intensa. Em proteínas contendo estes íons lantanídios a elas ligados, emissão de luz pode ser observada quando radiação no UV é absorvida por seus resíduos de aminoácidos aromáti-cos, indicando que há transferência de energia para o íon lantanídio. O presente trabalho foi feito com o objetivo de definir os sítios de ligação do Eu 3+ e do Tb 3+ nos complexos com os aminoácidos aromáticos L-fenilalanina e L-triptofano. As técnicas utilizadas foram as espectroscopias no infravermelho e de ressonância magnética nuclear de 13 C. Foi verificado que európio e térbio trivalentes interagem com o grupo carboxilato de ambos os aminoácidos. Com o L-triptofano o grupo imino do anel indólico também se liga ao lantanídio, representando um segundo ponto de coordenação.Trivalent europium and terbium ions have ionic radii similar to that of Ca 2+ . So they are employed as probes of calcium binding sites in biological molecules. These ions exhibit very useful spectroscopic characteristics, chiefly a pronounced luminescence. In protein bound lanthanide, visible light emission from the lanthanide excited states can be observed when UV light is absorbed by aromatic amino acids. Subsequently, the energy is transferred to the lanthanide ion. The present work was carried out to define the binding sites of Eu 3+ and Tb 3+ in complexes with the aromatic amino acids L-phenylalanine and L-tryptophan. The techniques utilized were infrared and 13 C nuclear magnetic resonance spectroscopies. It was found that trivalent europium and terbium interact with the carboxylate group of both amino acids. With L-tryptophan, the imino group of the indole ring is also involved representing another coordination site.

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