Supernormal Temperature Sensing Performance Realized through the Blue Emitting Level of Er along with Detection Ability in Deep Tissues.

Fluorescence intensity ratio (FIR)-type optical thermometers based on thermally coupled energy levels (TCLs) of rare earth ions are suitable candidates for noncontact temperature detection in living organisms, microelectronics apparatus, and so forth. Therefore, the improvement of the thermometric sensitivity of TCL-based thermometers has become a research hotspot in recent years. Herein, ultrahigh sensitivity and outstanding resolution for temperature sensing have been realized in YNbO: Yb/Er. Unusually, the thermally coupled three-level system of Er: F/H/S is first employed for optical thermometry based on FIR technology. A supernormal thermometric sensitivity of 2.67% K is obtained from the thermally coupled F and S states due to the large energy gap between them, significantly surpassing that of most temperature sensors in the same category. Furthermore, the existence of the intermediate level H can effectively prevent the decoupling effect between F and S. Additionally, the temperature sensing behavior realized by the Stark sublevels of the Er: I → I transition, with a penetration depth of 8 mm, shows the potential of temperature measurement in deep biological tissues, benefiting from its excitation and emission wavelengths located in the biological window. All of the data reveal that YNbO: Yb/Er is an ultrasensitive optical thermometer and exhibits the capacity of temperature detection in deep tissues.