Noncontact thermometry based on downconversion luminescence from Eu3+ doped LiNbO3 single crystal

An optical temperature sensor (OTS) based on the fluorescence intensity ratio (FIR) method of Eu3+ in LiNbO3 (LN) single crystal has been developed, and this OTS can effectively avoid the fluorescence measurement disturbance due to the low scattering factor of the host LN single crystal. The sensitivity achieved here is as high as 3916/T2 (4% K−1 at 303 K) in the temperature range of 303-723 K by using FIRs between 5D0-7F2 (625 nm) and 5D1-7F1 (541 nm), and it is significantly superior compared with using the FIRs between 5D1-7F1 and 5D0-7F1 of traditional thermally coupled levels (TCLs). Because of the high fluorescence efficiency of this sample, strong fluorescence intensity with high signal to noise ratio (SNR) is achieved under a low excitation power density of only 0.2 W/cm2. In our OTS system the average acquisition time of temperature is less than 2 s and the resolution is as high as 0.3 K at 573 K.