Comparison of Time and Frequency Domain Methods for Luminescence Lifetime Measurements

Despite the widespread use of luminescence lifetimes in physical measurements, there seems to be no consensus on the best method for lifetime determination. Researchers in this field split into two camps: those who favor methods that proceed from time-domain data and those who favor methods that proceed from frequency-domain data. System theory provides unique insight into the strengths and limitations of these methods of lifetime determination. First, system theory shows that the impulse response experiment and the frequency sweep experiment can both uniquely specify a shift-invariant linear system. Further, the time and frequency data sets are related by the Fourier transform. A careful comparison of these two methods was carried out with both numerical simulations and experiments using the same sample, light source, and detector. These comparisons were not limited to impulse and sine wave excitation; chirp, square wave, and random excitation sequences were evaluated as well. The results indicate that for the same total excitation energies time-domain sequences with a substantial dark period have the lowest uncertainty in the lifetime parameter estimates.