Analysis of phosphorescence decay in heterogeneous systems: Consequences of finite excitation flash duration

Analysis of phosphorescence lifetimes using the Stern-Volmer equation is a reliable means of determining quencher concentration for a uniform sample. Methods of analysis for heterogeneous systems are based on the assumption t hat the excitation is produced by a momentary flash. This condition is an i dealization because a real flash has a finite duration and a complex time p rofile. Zn the case of a heterogeneous quencher concentration, an excitatio n flash produces different initial intensities and different times of peak intensity from compartments having different concentrations of quencher, We formulated a model to explore the effects of hash duration on the shape of the emission curve obtained from systems in which the heterogeneity is con tinuous, We developed mathematical models that can be used to recover fitti ng parameters of continuous distributions of reciprocal lifetimes approxima ted as rectangular or Gaussian distributions, or an arbitrary histogram, We also formulated a procedure to convert the distribution of reciprocal life times into a volume distribution of quencher concentration, We found that ( 1) the Stern-Volmer ratio of phosphorescence intensities cannot be employed for interpretation of pulse phosphorometric data in terms of a volume dist ribution of quencher; (2) shortening the hash duration decreases the differ ence of initial intensities between compartments having high and low quench er concentration; (3) the parameters of the volume distribution of quencher concentration can be recovered correctly only after taking account of the difference in initial intensities; and (4) calibration of the initial inten sities for a given fitting delay and flash function is necessary.