A novel upconversion optical thermometers derived from non-thermal coupling levels of CaZnOS:Tm/Yb phosphors

The growing interest in precise, rapid and contactless optical temperature sensor has led to the more demand for novel materials. In this work, Tm3+/Yb3+ co-doped CaZnOS phosphors were synthesized via a simple method of precipitation. The upconversion luminescence (UC) properties and optical temperature behavior were investigated. The strongest UC intensity was achieved with the doping concentration of 1:9 (Tm:Yb) and the emission bands located at 483 ​nm, 652 ​nm and 792 ​nm were ascribed to 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions, respectively. The optical thermometry using fluorescence intensity ratio (FIR) based on non-thermal coupling levels (NTCLs, 1G4 and 3H4) was employed to assess temperature sensing performance through analyzing temperature-dependent UC spectra of CaZnOS: Tm/Yb (1:9) sample. The maximum sensing sensitivity was 0.0262 ​K−1 ​at 393 ​K, as a comparation, which is more than 20 times higher than that of thermal coupling levels (TCLs, 1G4(a), and 1G4(b)). The result shows the validity of optical thermometry based on NTCLs, simultaneously suggesting that CaZnOS has great potential in temperature sensors.