  We have studied the electronic properties and optical absorption spectra of
three different cases of donor centers, D^{0}, D^{-} and D^{2-}, which are
subjected to a perpendicular magnetic field, using the exact diagonalization
method. The energies of the lowest lying states are obtained as function of the
applied magnetic field strength B and the distance zeta between the positive
ion and the confinement xy-plane. Our calculations indicate that the positive
ion induces transitions in the ground-state, which can be observed clearly in
the absorption spectra, but as zeta goes to 0 the strength of the applied
magnetic field needed for a transition to occur tends to infinity.
