Luminescence thermometry with Gd₂O₂S: Yb³⁺ /Er³⁺ nanoparticles under different excitation pathways

Luminescence thermometry using lanthanide-doped nanoparticles has shown to be a forefront approach to measuring temperature at the nanoscale. Such thermometers have a special advantage due to the variety of excitation possibilities, ranging from infrared to ultraviolet. However, it is still uncertain whether the thermometric characteristics of a given lanthanide-based system remain the same regardless of the particular excitation condition. In this work, we investigate the thermometric response of Gd₂O₂S : Yb³⁺ /Er³⁺ nanoparticles under different excitation pathways, using wavelengths in the range between 800 nm and 1600 nm, and also by employing a simultaneous two-color excitation (1510 nm + 859 nm). We observe that the thermal sensitivities are similar under those excitation conditions, ranging from 1.16 %/K to 1.42 %/K, with the highest being obtained with the bichromatic excitation. Also, this non-conventional excitation regime suppresses the luminescence band originated from the transition ²H_9/2 → ⁴I_13/2 of the Er³⁺ ions, which is known to reduce the thermal sensitivity and mask the correct thermometric parameters. This study is a step towards increasing the luminescence thermometers’ reliability and accuracy, aiming at robust applications in different areas.