The rapid lifetime method (RLD) for determining excited-state lifetimes uses the ratio of the areas under two regions of the decay. To get good precision with the standard method, prior knowledge of the lifetime is essential to selecting the integration regions. As will be shown, the usual method of selecting integration regions is far from optimal. An optimal gating scheme that is more precise and much more forgiving in the selection of integration region than any of the prior methods will be shown. Monte Carlo simulations were performed to determine the optimal gating. Experimental data was used to confirm the capabilities of the optimized RLD. The speed of the optimal RLD is similar to the standard RLD but without the necessity of matching the integration interval to the lifetime for precise results.

For evaluating exponential luminescence decays, there are a variety of computational rapid integral methods based on the areas of the decay under different binned intervals. Using both Monte Carlo methods and experimental photon counting data, we compare the standard rapid lifetime determination method (SRLD), optimized rapid lifetime determination methods (ORLD), maximum likelihood estimator method (MLE), and the phase plane method (PPM). The different techniques are compared with respect to precision, accuracy, sensitivity to binning range, and the effect of baseline interference. The MLE provides the best overall precision, but requires 10 bins and is sensitive to very small uncorrected baselines. The ORLD provides nearly as good precision using only two bins and is much more immune to uncompensated baselines. The PPM requires more bins than the MLE and has systematic errors, but is largely resistant to baseline issues. Therefore, depending on the data acquisition method and the number of bins that can be readily employed, the ORLD and MLE are the preferred methods for reasonable signal-to-noise ratios.

A new gated form of phase fluorometry for measuring lifetimes is presented. The technique uses a square-wave excitation and gates the detector on only during the off period of the excitation. Using a long-lived sample, this eliminates or reduces errors from scattered light and short-lived fluorescences. Using a square-wave modulated excitation source with a 50% duty cycle, traditional data treatment can be used after, at most, a simple pi/2 phase adjustment. A combination of theory and experimental results demonstrates the validity of this new gated method and its utility for eliminating or reducing background. The results are precise, accurate, eliminate scattering errors, and greatly reduce errors due to short-lived fluorescence impurities. Errors from fluorescence bleed-through into the detection period or a slow excitation source turn off can be mitigated by using an offset time prior to gating the detector on.