DELAYED FLUORESCENCE OPTICAL THERMOMETRY

Acridine yellow dissolved in a rigid saccharide glass is proposed as a sensor material for optical thermometry. Following efficient excitation in the visible, triplet states of the dye are produced with a high quantum yield. Activated reverse intersystem crossing from the triplet to the singlet excited state, followed by delayed fluorescence, provides a temperature-dependent decay pathway that competes with phosphorescence to depopulate the triplet state. Either the triplet-state lifetime or ratio of delayed fluorescence-to-phosphorescence intensities may be used to monitor temperature. Lifetimes of >100 ms are observed at ambient temperatures which require modest instrumentation to measure and process. Since fluorescence and phosphorescence spectra are well separated, their intensity ratio can be determined using interference filters. The thermometer performance can be predicted from photophysical models for the temperature dependence of the triplet-state decay. The relative sensitivities of the triplet-state lifetime and of the ratio of delayed fluorescence-to-phosphorescence intensities to temperature over the range of -50 to 50 degrees C are 2.0 and 4.5%/degrees C, respectively, which are similar to 10 times greater than typical optical thermometers. The high sensitivities to temperature change result in temperature uncertainties of less than 1 degrees C over this range.