Upconversion Luminescence and Discussion of Sensitivity Improvement for Optical Temperature Sensing Application.

Upconversion (UC) based luminescent materials have promising applications in noncontact temperature sensors. How to improve the sensitivity is one main object at present. This work presented several strategies for optical temperature sensing based on UC spectra of the YWO:Yb-Er/Ho/Tm phosphors. The improvement for the relative ( S) and absolute ( S) sensitivities were discussed by using a fluorescence intensity ratio technique. It includes thermally coupled levels (TCLs) and non-TCLs. It was proposed that a piecewise expression could be employed to achieve high S value for TCLs. However, improving the S value is limited for TCLs. With regard to the non-TCLs, S and S are not restricted, but not easy to be improved synchronously. On the other hand, the morphology and UC spectra of the samples were also studied. The above investigation could be instructive to develop new luminescent materials with high sensitivity.