Luminescence Thermometry of Eu-Tb Mixed Metal-Organic Frameworks—Some Ways to Tune the Thermometric Performances

Since the discovery of the first ratiometric Eu-Tb-mixed MOF luminescent thermometer in 2012, the number of potential luminescent thermometers increases drastically, notably because of the inexhaustible choice of suitable organic ligands, and consequently the infinity of potential materials. Since then, the research on Eu-Tb mixed MOFs was summarized on the investigation of on single material with a specific lanthanide composition. Thus, as solid-state chemist, we have attempted for few years to identify the structural parameters which can govern or guide the thermometric performances, such as the use temperature range or the relative thermal sensitivity. Our objectives are to rationalize the research on Eu-Tb mixed MOFs for thermometry to design highly performant materials which could be proposed as an alternative of the well-recognized inorganic compounds.<br/>In Eu-Tb mixed MOFs, the organic ligand plays the role of structuring agent for the network but also of sensitizer for lanthanide emission (antenna effect). Thus, we decided to start our approach by investigating a series of MOFs built upon the same organic ligand but exhibiting different topologies of the Ln³⁺ polyhedra network (planes, chains, dimers…). We highlighted the important effect of the Eu/Tb ratio on the relative thermal sensitivity, but also the necessity to control the Tb-to-Eu energy transfer by using Gd³⁺ as diluting agent. This first results enabled us to design more sensitive luminescent thermometers in a controlled way. Finally, our first results have also evidenced the impact of the topology on the temperature sensing.