Highly sensitive and precise optical temperature sensors based on new luminescent Tb3+/Eu3+ tetrakis complexes with imidazolic counterions

Abstract

In the present work, new Tb3+/Eu3+ tetrakis(benzoyltrifluoroacetone) complexes containing imidazolic counterions were successfully prepared and characterized via elemental analysis, infrared spectroscopy, thermogravimetry, and X-ray powder diffraction. Photophysical features of the Eu3+ ion, such as the intrinsic emission quantum yields, radiative and non-radiative decay rates, and emission lifetimes were dramatically improved when compared with the data from the hydrated tris complex reported in the literature. The values found for the absolute emission quantum yields are up to 0.79 and ratiometric luminescent thermometers were built-up based on the ratio between the spectral areas of the 5D0 → 7F2 (Eu3+) and 5D4 → 7F5 (Tb3+) transitions. The best contactless temperature sensor operates in a wide temperature range (20–225 K) with a relative thermal sensitivity higher than 4% K−1 (maximum value of ∼7.6% K−1 at 20 K) and a temperature uncertainty lower than 0.1 K with a minimal lower than 0.01 K by combining excitation at the ligand (360 nm) and the Tb3+ ion (489 nm), illustrating the potential of lanthanide-based tetrakis complexes in the design of efficient luminescent thermometers.