Photomodulated cryogenic temperature sensing through a photochromic reaction in Na 0.5 Bi 2.5 Ta 2 O 9 : Er/Yb multicolour upconversion.

Optical temperature sensing of the non-thermally coupled energy levels (N-TCLs) based on fluorescence intensity ratio (FIR) technologies has excellent temperature sensitivity and signal recognition properties. In this study, a novel strategy is established to enhance the low-temperature sensing properties by controlling photochromic reaction process in NaBiTaO: Er/Yb samples. The maximum relative sensitivity reaches up to 5.99% K at cryogenic temperature of 153 K. After irradiation with commercial laser of 405 nm for 30 s, the relative sensitivity is increased to 6.81% K. The improvement is verified to originate from the coupling of optical thermometric and photochromic behaviour at the elevated temperatures. The strategy may open up a new avenue to improve the thermometric sensitivity in photo-stimuli response photochromic materials.