Tailoring Energy Transfer in Mixed Eu/Tb Metal-Organic Frameworks for Ratiometric Temperature Sensing.

Eu/Tb metal-organic frameworks (Eu/Tb-MOFs), exhibiting Eu and Tb emissions, stand out as some of the most fascinating luminescent thermometers. As the relative thermal sensitivity model is limited to its lack of precision for fitting ratio of Eu and Tb emissions, accurately predicting the sensing performance of Eu/Tb-MOFs remains a significant challenge. Herein, we report a series of luminescent Eu/Tb-MOF thermometers, EuTbL, with excellent thermal sensitivity around physiological levels, achieved through the tuning energy transfer from ligands to Eu and Tb and between the Ln ions. It was found that the singlet lowest-energy excited state () of the ligand and the higher triplet energy level () are crucial in the energy transfer processes of ligand→Tb and ligand→Eu. This enables EuTbL to serve as an effective platform for exploring the impact of these energy transfer processes on the temperature-sensing properties of luminescent Eu/Tb-MOF thermometers. The relative thermal sensitivity is comparable to that of dual-center MOF-based luminescent thermometers operating at physiological levels. This study provides valuable insights into the design of new Eu/Tb thermometers and the accurate prediction of their sensing performance.