Polymer films doped by Eu(III) complexes are promising candidates for the development of luminescent chemosensors. Here, luminescent properties of Eu(III) carboxylate dibenzoylmethanates in interaction with ammonia and amine vapors have been studied. Quantitative measurements of the optical response showed that with an increase of the analyte concentration in the range of 3–330 ppm, an increase in the luminescence intensity of europium(III) is observed. The reversibility of the luminescent response is established. Quantum chemical calculations showed that ammonia and amine molecules enter not in the Eu(III) coordination sphere, but forms hydrogen bonds between analyte molecules and carbonyl groups of the dibenzoylmethanate ion. Moreover, analyte changes ligand coordination mode: there occur the transformation from tridentate-bridging-cyclic coordination of carboxyl groups to bidentate-bridging which leads to decreasing in the efficiency of cross-relaxation of lanthanide ions. The obtained “turn-on” chemosensory polymer materials are promising for environmental monitoring and food safety testing.