Visual Luminescence Thermometry Enabled by Phase-Transition-Activated Cross Relaxation of Tb 3+ Ions

Abstract

The development of visual luminescent thermometers capable of exhibiting pronounced color changes in response to temperature variations requires the rational design of phosphors with high spectrally selective thermal sensitivity. In this work, we present a strategy based on phasetransition-induced activation of cross-relaxation processes in LiYO 2 :Tb 3+ . The monoclinic-totetragonal structural phase transition modifies the point symmetry of Tb 3+ ions in the host lattice, enhances the Stark effect, and enables energetic resonance required for efficient cross relaxation. Consequently, emission originating from the 5 D 3 excited state is rapidly quenched relative to that from the 5 D 4 level above approximately 300 K, resulting in a distinct temperature-dependent color change of the emitted light from blue to green. This mechanism yields exceptionally high chromaticity-coordinate-based sensitivities, reaching S Rx,max = 0.40% K -1 and S Ry,max =0.72% K -1 at 410 K. Furthermore, phase-transition-driven modifications of the Tb 3+ emission spectral profile enable the realization of a multimode luminescent thermometer with a maximum relative sensitivity of S Rmax =13% K -1 . The practical applicability of this system is demonstrated through an ON-OFF luminescent thermal switch and fully filter-free, dynamic two-dimensional thermal imaging using the blue and green channels of a standard digital camera, enabling intuitive visualization, remote readout, and temperature mapping under dynamic conditions.