Optical thermometry based on upconversion luminescence of Yb3+-Er3+ and Yb3+-Ho3+ doped Y6WO12 phosphors

The Yb³⁺-Er³⁺ and Yb³⁺-Ho³⁺ co-doped Y₆WO₁₂ (YWO) luminescent materials were synthesized successfully using the solid-state reaction method, and their phase purity, upconversion (UC) spectra, and optical temperature sensing properties were studied. Upon 980 nm excitation, the dominant emission peak around 660 nm is found in the YWO:Yb³⁺,Er³⁺ sample, which could be attributed to the Er³⁺F4_9/2-I4_15/2 electronic transition. Two green emission peaks of Er³⁺ appear in the range from 515-575 nm. For the YWO:Yb³⁺,Ho³⁺ phosphor, there are three emission peaks found at 548, 667, and 758 nm, which can be ascribed to the (F₄5,S5₂)-I5₈, F₅5-I5₈, and (F₄5,S5₂)-I5₇ transitions of Ho³⁺, respectively. By studying the emission intensity dependence of the pumping power, the result suggests that the two-photon process is involved for all the above emissions. In the temperature range of 293-553 K, the temperature sensing behavior of the typical YWO:10%Yb³⁺,1%Er³⁺ and YWO:10%Yb³⁺,1%Ho³⁺ phosphors was investigated in detail, and the results have been shown by using the fluorescence intensity ratio technique and decay curves. The above investigations indicate that the present UC phosphors could be promising phosphor materials for temperature sensor.