Engineering of Mixed Eu³⁺/Tb³⁺ Metal‐Organic Frameworks Luminescent Thermometers with Tunable Sensitivity

Abstract In the last decade, numerous Ln‐bearing metal‐organic frameworks (MOFs) have been reported for luminescence thermometry applications. Although the Ln³⁺ composition is always thoroughly determined, this parameter is never optimized to improve thermometric performances. Here, the optimization of thermometric performances of luminescent probes is tackled by reporting a series of mixed Eu³⁺–Tb³⁺ metal‐organic frameworks. The thermometric performances are accessed as a function of the Eu³⁺ content yielding a maximum relative sensitivity between 0.19 and 0.44% K⁻¹ registered at temperatures between 340 and 240 K, respectively. A meticulous theoretical investigation of the Tb³⁺‐to‐Eu³⁺ energy transfer in the series of mixed Eu³⁺–Tb³⁺ MOFs is also performed to determine the predominant pathway of the energy transfer. For the first time, a clear evidence of the significant influence of the Eu/Tb ratio on the energy transfer between Ln³⁺ emitting centers is presented that definitively determines the operating temperature range and the maximum relative sensitivity of the luminescent thermal probes.