Abstract

We present, to the best of our knowledge, a new method for differential temperature measurement based on thermal sensitivity of the fluorescence lifetime of thermographic phosphors. Pairs of thermographic phosphors are excited with intensity-modulated light at frequencies $\omega$ and $\omega +\mathrm{\Delta }\omega$. The phase shift $\mathrm{\Delta }\theta$ of the summary fluorescence intensity beat signal envelope is measured. A prototype of a fluorometric differential temperature sensor is developed, and feasibility of the method is experimentally demonstrated with a ${\mathrm{Sm}}^{2+}\text{:}\mathrm{SrFCl}$ crystal and the ${}^5{\mathrm{D}}_1->{{}^7\mathrm{F}}_0$ transition for high thermal sensitivity. The observed linear dependence between envelope phase shift $\mathrm{\Delta }\theta$ and temperature difference $\mathrm{\Delta }T$ agrees with the theoretical prediction. Sensitivity of $S=-0.97°/°\mathrm{C}$ was achieved. This method could also be applied to differential measurements of any parameter affecting fluorescence lifetime.

© 2018 Optical Society of America

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