Optical temperature sensing based on the variation of the fluorescence intensity ratio of rare-earth materials has become appealing due to its multiple superiorities over electrical temperature sensing. However, confined by the largest energy separation of two thermally linked levels of rare earth ions, the highest sensitivity of such temperature sensing is essentially smaller than 2878/T 2, as reported previously from diverse systems. In this work, we demonstrate that ultrahigh-sensitive temperature sensing can be achieved from Pr3+-doped (Ba0.7Sr0.3)TiO3 based on the intensity ratio of the 1D2-3H4 emission to the 3P0-3H4 emission. The ratio can be increased as much as 90-fold when the temperature rises from room temperature to 513 K, nicely fitting a thermally linked-levels like equation and showing an ultrahigh sensitivity of 4275.1/T 2. The striking change of the ratio is attributed to the interaction between the two emission levels and the intervalence charge transfer state. This work may have provided a distinct route in the field of optical temperature sensing utilizing rare-earth-doped materials. In addition, the resultant product also possesses excellent photoluminescence and ferroelectric properties, showing promising potentials in multifunctional devices for practical applications.
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