A theoretical framework for optical thermometry based on excited-state absorption and lifetimes of Eu3+ compounds

Ratiometric optical thermometers correspond to one of the most extensively studied applications of luminescent lanthanide materials in recent years. Even though several systems were studied involving the Eu3+ ion, few of them explore the absorption from the low-lying 7F1 excited state and its dependence on the ligand field (LF) splitting. This work aims to describe various absorption intensity ratios (AIR) that can be built from the excitation or absorption spectrum of the europium (III) ion by using the absorptions from the 7F0 → 5D0 transition and the different ligand field components of the magnetic-dipole allowed 7F1 → 5D0 transition and the influence of the ligand field strength on the relative thermal sensitivity of such AIR constructions. We have shown that several AIR formulas can be obtained, and they can display opposite behaviors concerning the Ligand Field strength, being suitable for different compounds of non-cubic symmetries. In addition, the ligand field influence on the relative thermal sensitivity obtained by the lifetime thermometry of the Eu3+ 5D0 level has also been explored.