Method for lifetime-based chemical sensing using the demodulation of the luminescence signal

A novel method for measuring the phosphorescence decay time of optical sensors is presented. It is based on the frequency domain measurement of the demodulation of luminescence signals. Two lock-in amplifiers are used in the set-up. The ratio of two amplitudes simultaneously measured at different modulation frequencies (f(1) and f(2)) corresponds to the luminescence demodulation and therefore to the decay time. The feasibility of the new method is demonstrated for an optical oxygen sensor. The decay time data obtained from the demodulation measurement are compared with those derived from the conventional phase detection. The well established two-site model for description of intensity calibration curves for oxygen partial pressure, was found to be also suitable to describe the decay time based calibration curves derived from the demodulation and from phase angles. (C) 2002 Published by Elsevier Science B.V.