Excitation powder dependent optical temperature behavior of Er³⁺ doped transparent Sr_0.69La_0.31F_2.31 glass ceramics.

The knowledge of the pump power for which the population of thermally coupled energy levels (TCL) changes with power increase is of valuable importance for optical temperature sensors. In this paper, novel Er³⁺ doped transparent Sr_0.69La_0.31F_2.31 glass ceramics was fabricated successfully, and its structure is studied by XRD, TEM and HRTEM analyses. The ²H_11/2/⁴S_3/2, ⁴F_9/2(1)/⁴F_9/2(2), and ⁴I_9/2(1)/⁴I_9/2(2) levels of Er³⁺ are proved as TCL by analyzing the temperature dependent fluorescence intensity ratios. The spectrum split, thermal quenching ratio, population stability, and temperature sensitivity from three TCL are observed to be dependent on the pump power. A new fitting method has been developed to establish the relation between fluorescence intensity ratios and temperature. It is found that the combined use of ²H_11/2/⁴S_3/2 and ⁴F_9/2(1)/⁴F_9/2(2) as thermally coupled energy levels will get a more precise temperature reading from 62.7 K to 800 K with the help of low excitation power at 66.8 mW/mm².