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

Abstract The luminescent properties of Eu 3+ 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, Na 3 Sc 2 (PO 4 ) 3 :Eu 3+ as a function of temperature and dopant ion concentration. As demonstrated, Na 3 Sc 2 (PO 4 ) 3 :Eu 3+ 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 Eu 3+ 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 Eu 3+ concentration. Importantly, this study demonstrates, for the first time, temperature imaging using only Eu 3+ ‐doped phosphor via a digital camera without the use of optical filters. These results position Na 3 Sc 2 (PO 4 ) 3 :Eu 3+ as a promising multifunctional material for advanced applications in contactless temperature sensing and thermal imaging.