Luminescent properties of lanthanide complexes and applications in security anti-counterfeiting and information encryption based on pH response

The development of advanced anti-counterfeiting strategies and materials based on rare earth luminescent materials has shown great applications in preventing serious counterfeiting forgery techniques. In this work, a series of lanthanide organic complexes [Ln3(PDC)3Bipy(H2O)3]·2H2O(Ln = Eu, Tb, EuxTb1-x, H2PDC: pyridine-3,5-dicarboxylicacid, H2Bipy: 2,2-bipyridine), were synthesized via hydrothermal method. The results of Fourier transform infrared spectra(FTIR), thermos-gravimetric analysis(TGA) and powder X-ray diffraction(XRD), illustrate that the complexes share similar structures. The complexes exhibit strong emission even with the presence of water molecules coordinated in the structure. By adjusting the Eu/Tb molar ratio of the complexes, tunable emission color from green, yellow to red was achieved. Furthermore, both the luminescence color and the intensity exhibit obvious changes when the pH of the solution (glycerol: H2O = 1:1 V/V) is varied from neutral to acid or to basicity. In addition, Eu3+ and Tb3+metal ions in the binuclear complexes respond differently to pH alteration, therefore the emission color and intensity of the binuclear complexes are tuned with pH. Based on the special pH response of the complexes, we demonstrated the potential utility of the samples for security anti-counterfeiting and information multiple encryption.