Refractory Oxide Phosphors for Optical Temperature Sensing

Accurately probing temperature fields during the operation of energy systems is paramount for evaluating and controlling the physiochemical processes that dictate the efficiency and durability of such systems. Despite the criticality of on-line temperature profile measurements in energy systems, many challenges remain regarding the implementation of real-time temperature-sensing diagnostic probes, particularly in high-temperature and hard-to-access environments. While thermocouples are well-known for their accuracy and sensitivity, they are limited to providing single-point measurements. On the other hand, pyrometry can provide two-dimensional measurements of thermal profiles, but the technique’s accuracy suffers from changes in emissivity and reflected radiation. To address this gap in temperature sensing technologies, thermosensitive phosphor materials — comprised of a crystalline host matrix doped with an optically active lanthanide — have been studied for their viability to function as non-contact optical temperature probes. The well-defined temperature-dependent luminescence response of thermosensitive phosphors enables these materials’ temperature sensing capabilities. Phosphor thermometry offers unique advantages over contact thermometry and pyrometry with respect to implementation for operando temperature sensing in energy-relevant systems, as they afford the potential to be integrated into coatings or seeded into fluid flows. Remote phosphor excitation by means of a pulsed laser would facilitate on-line multidimensional measurements of thermal fields. However, advancements in phosphor design for high-temperature optical thermometry has been impeded by the absence of rational guidelines regarding the selection of host–activator pairs to produce a desired thermometric response. In efforts to bridge this knowledge gap, our group has endeavored to elucidate what structural and electronic features of the host govern high-temperature luminescence quenching, and how synthetic control may be exerted over these features to tune the phosphor’s luminescence response.