Isostructural Tb³⁺/Eu³⁺ Co-Doped Metal–Organic Framework Based on Pyridine-Containing Dicarboxylate Ligands for Ratiometric Luminescence Temperature Sensing

Abstract

In this work, we prepared two types of isostructural Ln³⁺-based metal-organic frameworks (LnMOFs) under solvothermal conditions, where two structurally similar pyridine-containing dicarboxylate ligands, 6-(4-carboxyphenyl)nicotinic acid and [2,2'-bipyridine]-5,5'-dicarboxylic acid, were used as the organic linkers. The as-synthesized LnMOF compounds were characterized using single-crystal X-ray diffraction (XRD), powder XRD, and thermogravimetric analysis. With the lanthanide co-doping approach, two mixed LnMOFs, Tb_0.95Eu_0.05cpna and Tb_0.95Eu_0.05bpydc, were obtained and evaluated for application as potential ratiometric luminescence thermometers. The temperature-dependent luminescence of the two materials was investigated, and their emission intensities, luminescence lifetimes, and thermometric parameters were compared. They exhibit an excellent S-shaped response for temperatures in the range of 25-300 K, with favorable relative sensitivity and temperature uncertainty. Moreover, their color changes from green at 25 K to red at 300 K, so that they are also suitable as colorimetric luminescent probes.