  We report on an experiment in which the fluorescence decay time of 5P levels
of Rb atoms in a coated vapor cell exceeds several of milliseconds, many orders
of magnitude longer than normal decay time of excited of rubidium atoms. We
found that this peculiarly long - term decay is not exponential and can only be
observed in a high quality coated cell with a long lifetime of optical pumped
atoms on atomic ground-state sublevels. A numerical simulation based on a
complete density matrix is presented. It supports the population pumping
process through the ground-state sublevels of Rb atoms as the most plausible
mechanism for the observed phenomenon and it consistently demonstrates all the
relevant features of the experiment. The investigation can be used, for
example, to explore the quality of a various anti-relaxation coatings used for
the resonant cells.
