In this chapter, the donor impurity phenomena in spherical semiconductor quantum dots (QDs) are theoretically investigated. A comparative analysis is performed between single-electron and two-electron configurations, where a donor impurity is on-center located within the QD nano-sphere. The ground state energies are calculated both perturbatively and using the Hartree self-consistent method. The results exhibit a good agreement between the two approaches, affirming the reliability of the Hartree methodology in modeling negatively charged donor systems under quantum confinement. Additionally, the optical absorption features of neutral ( \(D^0\) ) and negatively charged ( \(D^-\) ) donor impurities are analyzed. Despite minor differences in spatial wavefunctions, \(D^-\) centers yield significantly higher transition energies due to the presence of two interacting electrons. These findings demonstrate that not only the ground state energy but also the excited-to-ground state energy separation is greater for \(D^-\) donors compared to \(D^0\) configurations. Such distinctions substantially influence the absorption transition rate, suggesting that donor type plays a critical role in determining the optoelectronic response of QD-based nanostructures. By establishing a clear relationship between impurity charge state, energy structure, and optical behavior, this study provides a valuable theoretical framework for future research in the field of nanophotonics and quantum electronics.