An Optical Fiber-Based Spectrometer for Measurement of Fluorescence Lifetimes

An instrument is described which measures fluorescence intensity and lifetime properties using a single optical fiber for the development of fiber optic chemical sensors. The instrument utilizes a fast-pulse nitrogen laser for excitation and a digital storage oscilloscope to provide time-resolved fluorescence decay curves. The time-resolved measurements permitted the separation of most of the scattered excitation radiation from the sample signal and allowed for analysis of samples exposed to ordinary room lighting. A method for determination of lifetimes from the time-resolved decays was developed based on the time-correlated single-photon counting method. The new method used reference fluorophore solutions to determine the instrument response function, including the influence of the optical fiber, and multiple decays were averaged to improve signal-to-noise and to provide statistical weighting for the analysis. The accuracy of the lifetime analysis was demonstrated by comparison of results for Stern-Volmer quenching of quinine sulfate by chloride ion (slope = 0.115 ± 0.001, int. = 1.04 ± 0.04, r2 = 0.9992) with a literature study on the same system (slope = 0.118 ± 0.002, int. = 1.06 ± 0.05, r2 = 0.9986). Measurement of the lifetime of pyrene in ethanol gave 17.8 ± 0.9 ns, while the value for coumarin was 3.82 ± 0.45 ns. When mixed together, two lifetimes with values of 17.43 ± 0.73 and 3.68 ± 1.30 ns were determined.