Up-conversion luminescence of Yb³⁺/Er³⁺ doped Gd₂O₃ phosphors for optical temperature sensing in green and red regions

In this work, the up-conversion luminescence of Yb ³⁺/Er³⁺ doped Gd₂O₃ phosphors for optical temperature sensing in green and red regions are investigated. The intense green (522 and 562 nm) and red emissions (660 and 682 nm) radiated from Er³⁺/Yb³⁺ tri-doped Gd₂O₃ phosphors are successfully realized via tuning the doping proportion of Er³⁺ and Yb³⁺. To evaluate their potential ability of optical thermometry in green light range and the first biological window, the temperature-dependent green and red emissions are investigated. Based on the florescence intensity ratio (FIR) of 522 and 562 nm, the absolute sensing sensitivities of Gd₂O₃: 1 mol% Er³⁺/4 mol% Yb³⁺ and Gd₂O₃: 1 mol% Er³⁺/6 mol% Yb³⁺ phosphors reach 1.16 and 1.2% K⁻¹ (523 K), respectively. In addition, the temperature sensing sensitivities based on the FIR of 660 and 682 nm reach 0.8 and 0.6% K⁻¹ (300 K), respectively. Moreover, the changes of FIR (Δ R) are smaller than 3% within the cycling heat and cool processes. These results reveal that Gd₂O₃:1mol%Er/4(6)mol%Yb phosphors are promising for FIR-based temperature sensing in high temperature via green emissions and room temperature via red emissions.