Luminescent Platform for Thermal Sensing and Imaging Based on Structural Phase‐Transition

The luminescent properties of Eu³⁺ ions are highly sensitive to changes in their local crystal environment. While this feature has been widely studied, its application in thermometers based on thermally induced structural phase transitions is a recent development. These thermometers often suffer from a narrow thermal operating range, prompting the search for new host materials. In this context, Na₃Sc₂(PO₄)₃:Eu³⁺ as a function of temperature and dopant ion concentration. As demonstrated, Na₃Sc₂(PO₄)₃:Eu³⁺ was investigated as a potential candidate. This material undergoes a reversible phase transition from a monoclinic to a trigonal structure, leading to significant changes in both the emission spectra and the luminescence decay of Eu³⁺ ions. These effects enable the development of both ratiometric and lifetime-based luminescent thermometers, achieving maximum relative sensitivities of 3.4% K^-1 and 1.0% K^-1, respectively. Furthermore, the thermal operating range can be tuned by adjusting the Eu³⁺ concentration. Importantly, this study demonstrates, for the first time, temperature imaging using only Eu³⁺-doped phosphor via a digital camera without the use of optical filters. These results position Na₃Sc₂(PO₄)₃:Eu³⁺ as a promising multifunctional material for advanced applications in contactless temperature sensing and thermal imaging.