Recent advances on metal oxide-based luminescence thermometry

Luminescence thermometry alleviates the difficulties associated with conventional methods for thermal sensing and provides outstanding opportunities for non-contact thermometry with high sensitivity and resolution. Among various luminescence thermometry probes, doped metal oxide phosphors with low toxicity, high chemical, thermal and photo-stability, and wide band gaps which can incorporate a wide variety of doping ions have been considered as the most favorite ones. The emergent development of doped metal oxide phosphors utilized in this field necessitates a categorization from a materials point of view. Although there are several books and review articles on luminescence thermometry, there is no reported review categorizing thermometric metal oxide phosphors from a materials' perspective. Hence, we have performed a detailed survey in this article on the latest advancements in metal oxide-based thermometric phosphors doped with lanthanides and/or transition metals with downshifting and upconversion emissions. We cover the two most utilized read-out methods for thermometry, i.e., luminescence intensity ratio (LIR) and rise/decay time thermometry determined by either single or multiple emitting centers. Regarding the LIR method, two electronic transitions among various possible energy levels are commonly explored for obtaining high thermal sensitivity, so here we have focused on reviewing various employed luminescent ions in terms of their explored electronic transitions in host materials. Thermometers are generally evaluated by their measured temperature accuracy and range within which they can function properly. Correspondingly we have discussed the luminescence thermometric performance of investigated metal oxide phosphors based on their reported sensitivity values and working temperature ranges via either of the read-out methods. We have also discussed some challenges and perspectives of metal oxide-based phosphors at the end of this review. The thermometric metal oxide-based phosphors and their achieved thermometric performance categorized in this review are expected to stimulate the search for a whole new set of thermometric phosphors for fundamental studies and potential applications.