Multipath optical thermometry realized by electronic levels and Stark sublevels of Er3+

High-performance optical thermometer that can operate in the long-wavelength range of the second near infrared (1500 nm-1700 nm, NIR-IIb) biological window is in desperate need for bio-medical treatment. In this paper, a multipath temperature sensor Y3NbO7: Yb3+/Er3+ with pure cubic phase is synthesized by the high temperature solid state method. Under the excitation of 980 nm wavelength, efficient green upconversion emission attributed to thermally coupled Er3+: 2H11/2/4S3/2 levels are found, through which an excellent tem-perature sensing properties are realized with the maximal absolute and relative sensitivity of approximately 0.54 % K-1 and 1.37 % K-1 as well as the minimal temperature resolution of about 0.024 K. More importantly, the sample exhibits remarkable temperature detection capacity in deep tissues, which is implemented by the ther-mally coupled Stark sublevels of Er3+: 4I13/2locating just in the NIR-IIb sub-window. Thanks to this appropriate response wavelength range, the maximal penetration depth of the NIR-IIb optical thermometer in the biological tissues can reach up to 8 mm. All the findings indicate that the present sample is a supernormal multipath thermometric probe with detectability in the deep biological tissues.