This work reports on the synthesis, characterization, and photophysical properties of the lanthanide compounds of general formula [Ln(β-dik)(NO3)2(phen)2], where β-dik = acetylacetone (acac), hexafluoroacetone (hfac), tenoyltrifluoroacetone (tta) and bezoylacetone (bzac), phen = 1-10-phenanthroline, and Ln = Eu3+ and Gd3+. These complexes were prepared by direct reaction among methanolic solutions of the Ln(NO3)3·6(H2O), β-dik and phen ligands in the ratios Ln:β-dik:phen of 1:1:2.[1] All complexes were characterized by complexometric titration with EDTA, CHN microanalysis, absorption spectroscopy in the infrared region (IR), thermogravimetric analysis, diffuse reflectance in the UV-Vis region and luminescence spectroscopies. The properties of the [Ln(β-dik)(NO3)2(phen)2] complexes were compared with those ones for the [Ln(β-dik)3(phen)] complexes. The [Eu(acac)(NO3)2(phen)2]·H2O compound had its molecular structure elucidated by the single-crystal x-ray technique, presenting the following cell parameters: Space group: P2/n; a(Å) = 11,1982; b(Å) = 9,7154; c(Å) = 13,3217; α(o)= 90,0; β(o)=101,569; (o)=90,0; V(Å3)=1419,94; Z=2. Diffuse reflectance spectra of the [Ln(β-dik)(NO3)2(phen)2] complexes showed an additional broad band, which may be assigned to a low energy LMCT state. The emission and excitation luminescence spectra, recorded at 300 and 77 K, were used to calculate the experimental intensities parameters and intrinsic quantum efficiency of Eu3+ complexes. Concerning the theoretical part of the work, geometries of the complexes were optimized at Sparkle/AM1 level and the localized molecular orbitals (LMO’s) were achieved using the Pipek-Mezey procedure. The contribution from each LMO to the total molecular polarizability () was calculated using B3LYP/aug-cc-pVDZ method with the GAMESS program. The effective ligand polarizabilities (’) values were calculated by adding up the polarizabilities from each LMO’s in specific regions near the atoms directly coordinated to the lanthanide ion. The effective polarizabilities data obtained for the isolated ligands showed that the α’ values for the nitrate ligands are lower values than those for the other ligands, probably because of their small size and high hardness. It was also observed that the substituent groups in the β-diketonate ligands play an important role on the α’ values. Interestingly, the asymmetric β-diketonates tta and bzac presented different α’ values for each oxygen donor atoms, whereas both oxygen donor atoms in the symmetric β-diketonates acac and hfac ligands exhibited similar α’ values. The values of polarizabilities in specific regions near the atoms directly coordinated to the lanthanide ion, together with charge factors (g) of donor atoms, were used for calculate theoretical intensity parameters, which were compared with those determined experimentally from the luminescence spectral data.