Tuning the sensitivity of Ln3+-based luminescent molecular thermometers through ligand design

Luminescence thermometry is being addressed as one of the most promising techniques to non-contact measurement of temperature with sub-micrometric resolution, due to the possibility of design the thermometer performance by the smart combination of emitting centers, ligands and host matrix. Numerous applications in microelectronic circuits and photonic devices will benefit of improved spatial and temporal resolution in the temperature imaging. In this paper we report three Ln3+-based (Ln=Eu, Tb) molecular thermometers co-doping an organic-inorganic hybrid matrix with Eu3+/Tb3+ chelates that differ in the ligand used. We show that the sensitivity of such thermometers can be tuned from 0.042±0.002 to 3.0±0.4% 
- K−1, in the 295-330 K range, through the wisest design of the ligand (and the ligand-hybrid host interactions). The maximum sensitivity value is one of the largest reported so far for luminescent ratiometric thermometers. Furthermore, we rationalize the increase on the performance of the molecular thermometers using a partial energy scheme involving the emitting levels of the Ln3+ ions and the singlet and triplet states of the ligands and the hybrid host.