Ba₂LuNbO₆:Er³⁺,Yb³⁺ up‐conversion phosphors for dual‐mode thermometry based on fluorescence intensity ratio

Fluorescence intensity ratio (FIR) thermometry has been regarded as new optical thermometry because of its faster response, higher sensitivity, and accuracy. However, improving the sensitivity is still a challenge. Here, Ba 2 LuNbO 6 :Er 3+ ,Yb 3+ up‐conversion specimens were synthesized, characterized, and designed for dual‐mode thermometry based on FIR. The 2 H 11/2 / 4 S 3/2 thermally coupled energy levels (TCELs) and 2 H 11/2 / 4 F 9/2 non‐TCELs (NTCELs) of Er 3+ were selected as two FIR modes for optical thermometry. The energy gap of 2 H 11/2 / 4 S 3/2 TCELs of Er 3+ in Ba 2 LuNbO 6 :Er 3+ ,Yb 3+ phosphors was confirmed as 977 cm −1 . Therefore, the maximal relative sensitivity ( S r ) of FIR based on TCELs is 1.53% K −1 @ 303 K. For FIR based on NTCELs, a higher maximal S r value of 1.81% K −1 @ 303 K is obtained, which surpasses other Er 3+ ‐doped up‐conversion specimens. In addition, the phosphors exhibit excellent thermal fatigue resistance and temperature resolution. Results suggest that Ba 2 LuNbO 6 :Er 3+ ,Yb 3+ specimens might be applied in the temperature sensing field.