Abstract
SummaryAn evaluation is made of a typical time‐correlated single photon counting apparatus using a D2‐filled gated flash lamp. The aim is to determine: (1) the valid flash lamp profile, and (2) the reliability and sensitivity of subnanosecond lifetime measurements. As model systems for very short‐lived fluorescence possessing single exponential decay, concentrated JV‐methylpiperidine (NMP) solutions in n‐hexane were used. Stern‐Volmer self‐quenching kinetics were observed over a concentration range of 0.508 M to 1.00 × 10‐4M. Solutions having known subnanosecond lifetimes were accordingly prepared. The flash lamp profile was altered so that the tail‐portion (time > 3.6 ns after maximum) was reduced by a factor of 0.80. This altered profile provided the best convoluted functions as compared with the observed fluorescence decay curves. For lifetimes less than about 1 ns, the full‐width‐tenth‐maximum values of the convoluted and observed decay functions were used as the criterion for best fit. Using highly concentrated NMP solutions, lifetimes of 0.30, 0.50, and 0.70 ns could be clearly distinguished; a lower limit for reliable measurement is placed at ca 0.2 ns for a flash lamp having a FWHM of 2.6 ns and a 1/e value of 0.8 ns.
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