Ultrasensitive Colorimetric Luminescence Thermometry by Progressive Phase Transition

Abstract Luminescent materials that display quick spectral responses to thermal stimuli have attracted pervasive attention in sensing technologies. Herein, a programmable luminescence color switching in lanthanide‐doped LiYO 2 under thermal stimuli, based on deliberate control of the monoclinic ( β ) to tetragonal ( α ) phase transition in the crystal lattice, is reported. Specifically, a lanthanide‐doping (Ln 3+ ) approach to fine‐tune the phase‐transition temperature in a wide range from 294 to 359 K is developed. Accordingly, an array of Ln 3+ ‐doped LiYO 2 crystals that exhibit progressive phase transition, and thus sequential color switching at gradually increasing temperatures, is constructed. The tunable optical response to thermal stimuli is harnessed for colorimetric temperature indication and quantitative detection, demonstrating superior sensitivity and temperature resolution ( S r = 26.1% K −1 , δT = 0.008 K). The advances in controlling the phase‐transition behavior of luminescent materials also offer exciting opportunities for high‐performance personalized health monitoring.