DELAYED FLUORESCENCE OPTICAL THERMOMETRY

Acridine yellow dissolved in a rigid saccharide glass is proposed as a sensor material for optical thermometry. Following efficient excitati on 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, provi des a temperature-dependent decay pathway that competes with phosphore scence to depopulate the triplet state. Either the triplet-state lifet ime or ratio of delayed fluorescence-to-phosphorescence intensities ma y 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 s eparated, their intensity ratio can be determined using interference f ilters. The thermometer performance can be predicted from photophysica l models for the temperature dependence of the triplet-state decay. Th e relative sensitivities of the triplet-state lifetime and of the rati o of delayed fluorescence-to-phosphorescence intensities to temperatur e over the range of -50 to 50 degrees C are 2.0 and 4.5%/degrees C, re spectively, 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.