Luminescence thermometry based on one-dimensional benzoato-bridged coordination polymers containing lanthanide ions

Abstract

Three 1D coordination polymers with benzoate bridges have been assembled in the presence of 18-crown-6-ether (18C6): ¹_∞[Tb(PhCOO)₃(H₂O)(EtOH)]·0.5(18C6) 1, ¹_∞[Eu(PhCOO)₃(H₂O)₂]·0.5(18C6) 2, ¹_∞[Nd(PhCOO)₃(H₂O)₂]·0.5(18C6) 3. Compounds 2 and 3 are isomorphous. The crown ether molecules co-crystallize with the resulting 1D coordination polymers and play an important role in the supramolecular architecture of the crystals. A molecular alloy was prepared in a similar way to compound 1 using TbCl₃·6H₂O and EuCl₃·6H₂O in a molar ratio of 95 : 5. The Eu^III ions have statistically substituted the Tb^III ions in the host lattice The luminescence thermometry performance of the Tb_0.95Eu_0.05 system was investigated using pulsed excitation into Tb^III absorption at 352 nm. The maximum S_r value is 1.88% K⁻¹ at 80 K which is slightly reduced at 1.60% K⁻¹ at 313 K. Time-gated emission spectroscopy, employed here for the first time, allows us to reduce the spectral overlap of Tb and Eu emissions in the 610 to 625 nm range by 100% at 80 K, from 18 to 9%. Compound 1 as well as the molecular alloy, Tb_0.95Eu_0.05, show X-ray induced luminescence.