Excited-State Double Exchange in Manganese-Doped ZnO Quantum Dots: A Time-Dependent Density-Functional Study

Abstract

The lowest-energy electronic excited states of ZnO quantum dots containing 1−3 Mn2+ ions have been studied by time-dependent density functional theory. The calculations show that these excited states involve holes with predominantly manganese 3d character and electrons delocalized in conduction-band-like orbitals, consistent with description of these lowest-energy excited states as charge-transfer (photoionization) states. When the quantum dot contains two or more distant Mn2+ ions, spin-dependent hole delocalization among the dopants is observed, with parallel Mn2+ spin alignment maximizing hole delocalization and excited state energy stabilization. This effect is proposed to arise from double exchange in the charge-transfer excited state.