Strategy for optical thermometry based on temperature-dependent charge transfer to the Eu3+ 4f-4f excitation intensity ratio in Sr3Lu(VO4)3:Eu3+ and CaWO4:Nd3+

) f-f transitions has been observed in the temperature-dependent excitation spectra and employed as the thermometric probe in ratiometric luminescent thermometry. The strategy applies to the FIR technique in lanthanide singly doped phosphors and eliminates the limitation of thermal-coupled levels. It opens up new possibilities of ratiometric optical thermometry. In addition, the derived maximum relative sensitivity is larger than the value obtained via thermal-coupled levels in the same sample. This illustrates that optical thermometry based on abnormal thermal quenching might be a feasible and effective method.