Developing "smart windows" for optical storage and temperature sensing based on KNN transparent ceramics

Smart windows have attracted considerable attention due to their wide applications in optical data storage, switchable sunroof and temperature sensing. The development strategy for smart windows is focused on performance design, enhancement and integration. However, developing integrated multi-functional smart windows in a single material remains a challenge. In this work, we have successfully prepared (K0.5Na0.5)0.95Ba0.04Er0.01NbO3 (4Ba-1Er-KNN) transparent ceramics for potential applications of temperature detection and optical information storage in smart windows. With alternating ultraviolet (UV) illumination and 300 °C thermal stimulation, the prepared 4Ba-1Er-KNN ceramics can not only achieve non-destructive luminescence readout, but also exhibits an ultra-high photochromic (PC) contrast with rapid response time of 1 s. Furthermore, based on the up-conversion (UC) photoluminescence (PL) intensity ratio of Er3+: 2H11/2/4S3/2 thermally coupled levels, excellent low-temperature sensing performance with the maximum relative sensitivity of 0.023 K−1 at 213 K is obtained. The integration between UC PL, PC response and temperature sensing performance makes it possible to develop multi-functional smart windows.