Upconversion luminescence and temperature sensing properties of Ho,Yb-codoped BiWO.

Ho and Yb-codoped BiWO upconversion luminescent materials at different concentrations were prepared a high-temperature solid-phase method. The X-ray diffraction patterns showed that Ho and Yb doping basically did not affect the orthorhombic crystal system structure of the BiWO matrix material. Scanning electron microscopy images showed that 3%Ho,10%Yb:BiWO consisted of irregular bulk particles with sizes in the range of 0.5-2 μm and some powder agglomeration. SEM mapping and EDS measurements of the powder showed that the elements were relatively uniformly distributed. Under 980 nm excitation, the emission intensity of Ho was the largest for the 3%Ho- and 10%Yb-doped sample. With an excitation power ranging from 45 mW to 283 mW for the 3%Ho,10%Yb:BiWO sample, the relationship between the luminescence intensity and pump power was determined; the results indicated that the Ho (538 nm, 546 nm, 660 nm, 756 nm) emission peaks originated from two-photon absorption. In the temperature range of 298 K-573 K, under 980 nm laser excitation, the maximum absolute temperature sensitivity was 0.029% K (373 K), the maximum relative temperature sensitivity was 0.034% K (348 K) for the Ho thermally coupled energy levels F/S, and the minimum temperature resolution δ was 1.2857 K (298 K). Under the same conditions, the maximum was 51.02% K (573 K), the maximum was 1.85% K (523 K) for the Ho nonthermally coupled energy levels F/F, and the minimum δ is 0.2477 K (448 K). The colour coordinates showed that the luminescence of the 3%Ho,10%Yb:BiWO sample gradually shifted from the green region to the red region with increasing temperature.