  In this letter, we propose a new model to determine the recombination
oscillator strength of trions and biexcitons for bound and unbound cases in the
effective mass approximation. The validity of our model has been confirmed by
the radiative lifetime of the trion and biexciton in a spherical quantum dot.
The results show that the model works sufficient accuracy in comparison with
results of more complex methods such as quantum monte carlo techniques and
atomistic calculations.
