Abstract
We investigate theoretically the effects of isovalent substitutional doping on the optical properties of cubic MgO nanoparticles. The Ca, Sr, and Ba impurities preferentially occupy the three-coordinated cation sites and counterbalance the lattice strain induced by the finite size of the host particles. The lowest optical absorption band shifts to the lower energies as the radius of the substitutional species increases. Two types of nearly iso-energetic triplet excitons are found: the symmetric and asymmetric configurations correspond to the hole component being delocalized over three four-coordinated anion and localized on a single anion, respectively. The photoluminescence energies strongly depend on the exciton configuration and can be controlled by the judicious choice of the dopans.