Ho³⁺ and Yb³⁺-codoped Bi₂WO₆ upconversion luminescent materials at different concentrations were prepared via a high-temperature solid-phase method. The X-ray diffraction patterns showed that Ho³⁺ and Yb³⁺ doping basically did not affect the orthorhombic crystal system structure of the Bi₂WO₆ matrix material. Scanning electron microscopy images showed that 3%Ho³⁺,10%Yb³⁺:Bi₂WO₆ 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 Ho³⁺ was the largest for the 3%Ho³⁺- and 10%Yb³⁺-doped sample. With an excitation power ranging from 45 mW to 283 mW for the 3%Ho³⁺,10%Yb³⁺:Bi₂WO₆ sample, the relationship between the luminescence intensity and pump power was determined; the results indicated that the Ho³⁺ (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 S_a was 0.029% K^-1 (373 K), the maximum relative temperature sensitivity S_r was 0.034% K^-1 (348 K) for the Ho³⁺ thermally coupled energy levels ⁵F₄/⁵S₂, and the minimum temperature resolution δT was 1.2857 K (298 K). Under the same conditions, the maximum S_a was 51.02% K^-1 (573 K), the maximum S_r was 1.85% K^-1 (523 K) for the Ho³⁺ nonthermally coupled energy levels ⁵F₅/⁵F₄, and the minimum δT is 0.2477 K (448 K). The colour coordinates showed that the luminescence of the 3%Ho³⁺,10%Yb³⁺:Bi₂WO₆ sample gradually shifted from the green region to the red region with increasing temperature.

Mengliang Jiang

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