The effect of ligand symmetry on the ratiometric luminescence characteristics of lanthanides

Abstract

This work demonstrated that the ligand symmetry of europium(III) complexes controls the ratiometric luminescence characteristics of lanthanides. Nona-coordinated europium(III) complexes having unsymmetrical β-diketonate ligands (C_s) exhibit distinctive ratiometric spectral variations in the extremely narrow f–f transition bands over the temperature range from 253 to 323 K. In contrast, no such ratiometric change can be observed in a series of nona-coordinated europium(III) complexes containing symmetrical β-diketonate ligands (C_2v). The remarkable difference depending on the ligand symmetry (C_svs. C_2v) suggests that the coordination rearrangement of β-diketonate in the complex causes ratiometric spectral variations in extremely narrow f–f transition bands, where two europium(III) complex isomers exist in the solution equilibrium. A self-calibration method using dual iso-emissive points is reported, where self-calibration using the two emission intensities at the iso-emissive points reduces the coefficient of variation in luminescence thermometry.