Super-Poissonian statistics of on-off jumps in blinking fluorescence of single molecules.

Blinking fluorescence of a single guest molecule embedded in a polymer matrix and excited by cw laser light is considered. Such fluorescence exhibits quantum jumps from bright on-intervals to dark off-intervals, i.e., so-called on-->off jumps. A system with one type of on-intervals and with two types of off-intervals is studied. A distribution function w(N)(T) for the number N of on-->off jumps in a time interval T is derived. The distribution function is expressed via a threefold integral of three Poissonian functions, each of which relates to the corresponding exponential process in the quantum dynamics of a fluorescent impurity center. Numerical calculations of the distribution function w(N)(T) for four time intervals T of various durations are carried out. The distribution function w(N)(T) is broader as compared with the Poissonian one and has two maxima, one of which relates to observed time intervals without on-->off jumps.