Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone, Bearing Pyrazole Moiety and CHF2-Group: Structure, Color Tuning, and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL(3)(H2O)(2)], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [EuxTb1-xL3(H2O)(2)] (EuxTb1-xL3), [EuxGd(1-x)L(3)(H2O)(2)] (EuxGd1-xL3), and [GdxTb1-xL3(H2O)(2)] (GdxTb1-xL3), were studied. The EuxTb1-xL3 complexes exhibit the simultaneous emission of both Eu3+ and Tb3+ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu3+. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb3+ and Eu3+ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation.

Automated summary

The study investigates the luminescent properties of novel lanthanide complexes with different ions, showing that the EuxTb1-xL3 complexes emit both Eu3+ and Tb3+ ions simultaneously, with the luminescence color changing rapidly from green to red upon adding a small amount of Eu3+. A detailed analysis of luminescence decay allowed for determining the radiative lifetimes of Tb3+ and Eu3+ and estimating the rate of excitation energy transfer between these ions.