Robust Multimodal Thermometers Based on Gallium Oxide Microwires

Optical transduction for temperature sensors is an attractive approach that allows both a non-contact-mode and remote measurement of local temperature. Optical sensors can operate as luminescent or interferometric sensors, depending on the observable parameter to quantify the temperature. In the case of Ga₂O₃, Cr doped crystals can be used to monitor the local temperature through the study of the evolution of the characteristic R-lines of Cr³⁺ ions in this host. This has been probed to work nicely in the low temperature range, up to room temperature, since above RT, the R-lines emission overlaps with the broad phonon-assisted band due to the electron-phonon coupling. On the other hand, interferometric sensors can operate at higher temperatures, if the material system holds optical resonances.<br/>In this work, we present the multimodal sensor behavior of the luminescent and interferometric properties of optical microcavities based on Cr doped Ga₂O₃ microwires, in which the optical mirrors are Distributed Bragg Reflectors (DBR) built by a suitable combination of alternate layers of TiO₂/Al₂O₃ fabricated by Atomic Layer Deposition (ALD) to favor optical resonances in the near-infrared broad band related to Cr ions in Ga₂O₃. The results show that the system can operate as a thermometer with a 1 K resolution, from low up to high temperatures. The robustness of the temperature sensor has been assessed against laser irradiation, liquid environment and stability at high temperatures. The results confirm the potential of this device to work under extreme conditions.