A simple, compact, low-cost, highly efficient thermometer based on green fluorescence of Er^{3 +}/Yb^{3 +}-codoped NaYF₄ microcrystals

We developed a highly efficient optical thermometer based on intensity ratio of upconversion green fluorescence of Er^{3 +}/Yb^{3 +}-codoped NaYF₄ microcrystals. The sensor consists simply of a 980 nm laser diode, one narrow-band interference filter, two lenses, one Si-photocell and one multimeter, while being without use of spectrometer and additional electronics. The device not only has a simple, compact structure (hence a low cost), but also displays highly efficient sensing performance, characterized by large signal-to-noise ratio due to strong fluorescence intensity, high thermal resolution and sensitivity, which have the values 1.3 K and 1.24 × 10^{− 2} K^{− 1}, respectively, at the physiological temperature 310 K. The excellent sensing performance of the device was further confirmed by the results of the measurements repeated using a spectrometer. The thermometer is highly generalized that can be applied to other luminescent materials, and shows great potential for the physiological temperature sensing in biological tissues and cells.