Exciplex liquid-phase thermometer using time-resolved laser-induced fluorescence

Pulsed photoexcitation of hydrocarbon fuels doped with organic molecules exhibits a temperature-dependent fluorescence spectrum that is used as the basis for a weakly intrusive optical thermometer. By use of pulsed excitation from a 308-nm 8-ns XeCl excimer laser with gated detection of the fluorescence emissions from doped n -heptane, we demonstrate that time-resolved measurement of the excited monomer and the redshifted excited-state complex (exciplex) fluorescence emissions can yield sub-1 degrees accuracy for temperatures ranging from 440 K to the vicinity of the critical temperature (540 K). The experiments also show that the exciplex fluorescence spectrum is pressure independent below and above supercritical pressure.