Visualized thermal history sensor based on the rare-earth-doped zirconia

Temperature is one of the most fundamental parameters, and its accurate measurement is critically important for thermal systems. Despite substantial progress in temperature measuring techniques, design and fabrication of a reliable thermal history sensor, which can remember thermal events, still remain a significant challenge. In this Letter, we propose and experimentally demonstrate a new thermal history sensor based on the rare-earth-activated and yttria-stabilized zirconia (YSZ). This material candidate exhibits strong heat-treatment-dependent upconversion emission color. The structure and optical characterizations indicate that the phenomenon originates from the cooperative effects of multiple physical parameters, including crystallinity, crystal size, and the quantity of residual OH. This allows us to achieve excellent linear relationship between the heat-treatment temperature and the intensity ratio of the green and red emission band over a wide temperature range from 800°C to 1350°C. Thus, the thermal history information can be directly judged based on the emission color. These results provide a major step forward in expanding the scope of thermal history sensor materials.