Recent advances on visible and near-infrared thermometric phosphors with ambient temperature sensitivity: A review

The quantification of the exact temperature with precision is fundamentally vital for scientific exploration and industrial production. As a result, the accuracy of regular thermometers is currently questionable for measuring the temperature at sub-micrometric spatial resolution. Hence, there is a high demand for advanced non-contact thermometer sensors, which aid in the alternative fabrication of luminescence thermometry to monitor the temperature with precision accuracy. Therefore, the current review article focuses on the recent advances in luminescence thermometry, also known as optical thermometry, and its applications in biomedical imaging and intracellular temperature sensing. The review will also provide a detailed discussion concerning spectroscopic approaches for temperature read-out, and different materials utilized in this field, including organic compounds, quantum dots, metal nanoclusters-based, upconverting nanoparticles, dye-doped nanoparticles, and luminescence thermometry based on rare-earths. Furthermore, covered is the synthesis of rare earth elements and post-transition metals-based near-infrared thermometric phosphors. Nonetheless, more research is required to completely comprehend the properties and realize the potential applications of these materials. To create high-performing thermometers with desired properties and thermometric parameters, it is crucial to have a deep understanding of the material parameters that affect the thermometric performance of the phosphor. This includes understanding the role of these parameters that relate to sensitivity. Furthermore, the temperature sensitivity also depends on the synthesis and size of the material for thermometry applications. As a result, more efforts are needed to improve the current synthesis methods that offer the nanoparticles because they have poor luminescence and a very low photoluminescence quantum yield. Lastly, we discuss notable factors influencing the sensitivity of optical thermometers and their future directions.