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.

A new rapid lifetime determination method (RLD) that uses a rectangular excitation is presented. The information from the exciting, as well as the emitting, portion is used to extract decay parameters for a single exponential decay. The lifetime is computed from the ratio of the integrals of the emission during the excitation period and an equal time interval during the decay (Δt). The new square-wave RLD method (SWRLD) shows speed similar to the standard RLD method but without the necessity of matching Δt to the lifetime for precise results. Monte Carlo simulations are used to predict the capabilities of the SWRLD, and the theory is tested with a luminescent terbium complex. The method is particularly applicable to rapid lifetime analysis for high-performance liquid chromatography (HPLC) and for fluorescence microscopy. It lends itself to use with inexpensive square-wave modulated light-emitting diodes (LEDs).

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