A series of europium Eu- and La-doped complexes with two different crystal structures, namely, EuxLa1–x(phen)2(NO3)3 [phen = 1,10-phenanthroline, x = 1.0 (1), 0.88 (2), 0.73 (3), and 0.52 (4)] and {[EuxLa1–x(phen)2(H2O)2(NO3)2](NO3)·2(phen)(H2O)} [x = 0.28 (5) and 0.0 (6)], were synthesized in aqueous solution by using different Eu/La ratios.The complexes were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetry, and scanning electron microscopy. Compounds 1–4 and 5, 6 were obtained for Eu/La molar ratios higher than 5:5 and smaller than 3:7, respectively. The photoluminescence properties of these compounds depend on the crystal structure, which is determined by the Eu/La reactant ratio. Complexes 1–4 exhibit a quantum efficiency (η = 55 %) and quantum yield (q = 31 %) higher than 5 (η = 23 % and q = 6 %). The photophysical properties assessed by using the LUMPAC software are in good accord with the experimental values, particularly, the calculated (26 %) and measured emission quantum yields (31 %; excitation at the ligands at 255 nm).