A complete set of integral equations is used to describe the kinetics of reversible photo-ionization after instantaneous excitation, including “geminate” and bimolecular charge recombination to either the ground or excited states of neutral reactants. The excitations restored by bimolecular recombination of ions produce the delayed fluorescence which goes to zero as a second power of time.The fluorescence kinetics previously obtained with the spin-less Integral Encounter Theory (IET) and distant dependent rates of electron transfer is essentially corrected using Modified Encounter Theory (MET). The delayed fluorescence dependence on conversion rate is explained analytically on the simpler example of contact ionization and recombination.