Influence of the multiphonon non-radiative relaxation on the luminescence ratiometric thermometry

We take the ²H_11/2/⁴S_3/2-⁴I_15/2 transitions of Er³⁺ as examples to study the role of thermal quenching mechanisms, especially the multiphonon non-radiative relaxation (MNR), in determination of the luminescence ratiometric thermometry. A convenient method to effectively confirm the existence of the quenching mechanism is proposed, namely the piecewise fitting in several small temperature ranges. Based on this method, a series of fitted gaps between the ²H_11/2 and ⁴S_3/2 states of Er³⁺ are obtained, which are found to decrease monotonically with the increase of temperature. Undoubtedly, it suggests that the quenching mechanism is present. Furthermore, it is demonstrated that the MNR process which depopulates the distribution of the ²H_11/2 and ⁴S_3/2 states is likely to be mainly responsible for these gradually decreasing gaps.