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

The performance of the two most promising fluorescence-based temperature se nsing techniques, namely the fluorescence intensity ratio (FIR) and fluores cence lifetime (FL) schemes, have been compared. Theoretical calibration gr aphs for the two methods illustrate the useful monotonic change of the resp onse with temperature variation. Comparison of the responses and the sensit ivities of the two schemes show that at very low temperatures the FIR metho d 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 t imes and shorter intrinsic lifetimes of the upper energy levels) share a si milar sensitivity over a wide temperature range. The presence of a long rel axation time or a longer intrinsic lifetime of the upper level in the use o f the FL method gives a less satisfactory response. Experimental data obtai ned for a range of dopant ions in various host materials are found to be co nsistent with the theoretical expectation, with each material having a spec ific 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. (C) 1998 American Institute of Physics. [S0021- 8979(98)04821-X].