Comparison of fluorescence-based temperature sensor schemes: Theoretical analysis and experimental validation

The performance of the two most promising fluorescence-based temperature sensing techniques, namely the fluorescence intensity ratio (FIR) and fluorescence lifetime (FL) schemes, have been compared. Theoretical calibration graphs for the two methods illustrate the useful monotonic change of the response with temperature variation. Comparison of the responses and the sensitivities of the two schemes show that at very low temperatures the FIR method exhibits a significant variation with temperature, while the response of the FL method becomes constant with its sensitivity approaching zero. With increasing temperature, the FIR and the FL methods (with short relaxation times and shorter intrinsic lifetimes of the upper energy levels) share a similar sensitivity over a wide temperature range. The presence of a long relaxation time or a longer intrinsic lifetime of the upper level in the use of the FL method gives a less satisfactory response. Experimental data obtained for a range of dopant ions in various host materials are found to be consistent with the theoretical expectation, with each material having a specific energy gap difference. The sensitivities of each material are compared graphically which would allow the most appropriate sensor for an intended application to be selected.