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, Ba2LuNbO6:Er3+,Yb3+ up‐conversion specimens were synthesized, characterized, and designed for dual‐mode thermometry based on FIR. The 2H11/2/4S3/2 thermally coupled energy levels (TCELs) and 2H11/2/4F9/2 non‐TCELs (NTCELs) of Er3+ were selected as two FIR modes for optical thermometry. The energy gap of 2H11/2/4S3/2 TCELs of Er3+ in Ba2LuNbO6:Er3+,Yb3+ phosphors was confirmed as 977 cm−1. Therefore, the maximal relative sensitivity (Sr) of FIR based on TCELs is 1.53% K−1 @ 303 K. For FIR based on NTCELs, a higher maximal Sr value of 1.81% K−1 @ 303 K is obtained, which surpasses other Er3+‐doped up‐conversion specimens. In addition, the phosphors exhibit excellent thermal fatigue resistance and temperature resolution. Results suggest that Ba2LuNbO6:Er3+,Yb3+ specimens might be applied in the temperature sensing field. [ABSTRACT FROM AUTHOR]