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

In the last decade, numerous Ln-bearing metal-organic frameworks (MOFs) have been reported for luminescence thermometry applications. Although the Ln(3+) 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 Ln(3+) emitting centers is presented that definitively determines the operating temperature range and the maximum relative sensitivity of the luminescent thermal probes.

Automated summary

This study optimizes the thermometric performances of luminescent probes by reporting a series of mixed Eu3+-Tb3+ metal-organic frameworks, showing a maximum relative sensitivity between 0.19 and 0.44% K-1 at temperatures between 240 and 340 K. Additionally, a meticulous theoretical investigation of the Tb3+-to-Eu3+ energy transfer was conducted to determine the predominant pathway of the energy transfer, providing clear evidence of the significant influence of the Eu/Tb ratio on the energy transfer between Ln(3+) emitting centers.