Abstracts Chemistry

Lifetime measurements on pressure sensitive paints: temperature correction, effects of environment, and trials on new luminescent materials

by Lisa M. Coyle

Several studies involving lifetime measurements of pressure sensitive paint are presented. The issues investigated in these studies include: (i) fitting the time-resolved data (ii) understanding temperature dependence (iii) correcting for temperature dependence (iv) effects of environment and (v) evaluating new luminescent materials. The main findings are summarized as follows. One problem with lifetime measurements is fitting the time-resolved data. Single, double, and triple exponentials are frequently used; however, these functions often do not describe the data well or are they physically meaningful. To explore this issue other functions are used here: a stretched exponential, a time-offset stretched exponential, and an exponential with an added term for polymer interactions. While the single exponential fit to the data provides the most convenient means for determining pressure, in some cases a time-offset stretched exponential better reproduces the data. The temperature dependence of the emission intensity of PtTFPP in FEB is found to be composed of two roughly equal parts: the intrinsic temperature dependence of the lifetime and the temperature dependence of the absorbance. The temperature dependence of the lifetime (or emission intensity) creates an error in the predicted pressure due to temperature drifts across the airfoil and in the windtunnel. This error can be corrected for by using a paint containing La 2O2S:Eu3+. The pressure-independent, temperature-dependent europium lifetime is used to determine the temperature and thus appropriate Stem Volmer constants. The pressure can then be calculated more accurately from the PtTFPP lifetime. In addition, lifetime measurements are able to account for the anomalous temperature dependence of two molecules: SiOEP and AlOEP. The delayed fluorescence of these molecules causes the emission intensity to increase with increasing temperature. Two unexpected results are reported: vacuum lifetimes of a given molecule are found to depend on the polymer; bimolecular quenching constants for a given polymer are found to depend on the dye. Finally, a number of alternate pressure sensors were evaluated for use in pressure sensitive paints. None of the molecules in the study had superior properties to PtTFPP, the current sensor.