Three isostructural hexanuclear lanthanide–organic frameworks for sensitive luminescence temperature sensing over a wide range

Abstract

Temperature sensing plays essential roles in both fundamental research and high-tech applications. In this work, three isomorphic hexanuclear lanthanide metal–organic frameworks (Ln-MOFs), Ln(BPDC-xN) (Ln = Eu³⁺/Tb³⁺, x = 0, 1, 2) were prepared based on the cluster-based synthesis strategy with three structurally similar dicarboxylate ligands 4,4′-biphenyldicarboxylic acid (H₂BPDC-0N), 6-(4-carboxyphenyl)nicotinic acid (H₂BPDC-1N), and [2,2′-bipyridine]-5,5′-dicarboxylic acid (H₂BPDC-2N) as the organic linkers. The as-synthesized Ln-MOFs were fully characterized using single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), elemental analysis (EA), and Fourier transform infrared spectra (FT-IR). Using a Eu³⁺/Tb³⁺ co-doping approach, Eu_0.001Tb_0.999(BPDC-xN) (x = 0, 1, 2) were identified as potential ratiometric luminescence thermometers. Since there are two suitable distances between the energy donors and acceptors within the framework for efficient energy transfer, all Eu_0.001Tb_0.999(BPDC-xN) (x = 0, 1, 2) maintain high relative sensitivity over a wide temperature range from 50 K to 300 K.