Ultra-sensitive luminescent ratiometric thermometry based on matrix energy transfer in Dy3+ doped CaWO4 phosphors

In this paper, we report the photoluminescence (PL) properties of the WO42− group and Dy3+ ions for a new highly sensitive luminescent ratiometric thermometry in Dy3+ doped CaWO4 (CaWO4:Dy) phosphors. Under 259 nm excitation, the violet emission from the WO42− group, as well as the blue and yellow emissions of Dy3+ from the transitions of thermally coupled energy levels (TCLs) of 4I15/2 and 4F9/2, were both investigated, which ascribed to an energy transfer from WO42− to Dy3+. The thermal-enhanced PL of Dy3+ and the thermal-quenched PL of WO42− were detected with increasing temperature. By taking advantage of the opposite temperature-dependent PL evolution, a new thermometry strategy was proposed based on the luminescence intensity ratio (LIR) between Dy3+ and WO42− having a quantitative relationship with temperature. The maximum absolute and relative temperature sensing sensitivities were as high as 449.52*10−4 K−1 and 21.03% K−1 at 300 K, respectively, which were superior to those reported previously for traditional TCLs-based LIR thermometry. This study demonstrated the potential of CaWO4:Dy phosphors in temperature sensing and provided guidance for constructing an effective ratiometric thermometry strategy with excellent and reliable sensing performance.