Upconversion luminescence of Yb3+-Ho3+co-doped Y18(WO4)4O23 phosphors for optical thermometers

The Yb3+-Ho3+ co-doped Y18W4O39 (YW) phosphors were prepared by using solid-state reaction method, and the upconversion (UC) luminescence was investigated for applications in optical thermometer. The single-phase samples were determined by the XRD patterns. The absorption peaks of the doping ions were attributed in the diffuse reflection spectra. Under 980 nm light excitation, the green and red emissions of Ho3+ were observed, and the optimal Ho3+ concentration was determined to be 0.5 mol%. The corresponding concentration quenching mechanism was well explained. The temperature-quenching spectra revealed that the intensities of both the green and red emissions were immensely sensitive to temperature but showed different decline rates with rising temperature, which indicated the possible applications in optical temperature sensing with fluorescence intensity ratio (FIR) strategy. The maximum absolute and relative sensitivities were obtained to be 0.0179 and 0.68% K-1 at 298 K, respectively. Furthermore, the population way on 5F5 level of Ho3+ was clarified to better understand the UC mechanism. The above investigations suggest that the YW:Yb3+,Ho3+ phosphor shows potential appli-cations in optical thermometer.