Optical temperature-sensing properties with various strategies for Y18W4O39 phosphors by near-infrared excitation

The Er3+-Yb3+ and Tm3+-Yb3+ rare earth (RE) ions co-doped Y18W4O39 (YWO) phosphors were prepared by the solid-state reaction method. Their phase purity, upconversion (UC) luminescence and optical temperature sensing behaviors were investigated in detail. The single-phase samples are obtained when the RE ions are incorporated into the YWO host lattice. The characteristic transition peaks of Er3+ and Tm3+ appear under irradiation with the 980 nm laser light source and their optimal doping concentrations are determined. The fluorescence intensity ratio (FIR) strategy is utilized to assess the optical temperature-sensing properties, including the thermally coupled energy levels (TCELs) and non-TCELs. It is found that the FIRs of Er3+ (I524/I546 and I659/I524) and Tm3+ (I477/I484 and I791/I652) change obviously as the temperature varies. The temperature-induced changes for FIRs are also checked, which indicates an excellent reproducibility and repeatability. A series of sensitivity curves are presented as a function of absolute temperature, and the maximum sensitivity values are obtained. Furthermore, the decay curves are studied to better understand the UC energy transfer process. The above results reveal that the developed phosphors are promising to be a candidate for optical temperature sensor.