Seminarium "Teoria i Modelowanie Nanostruktur"

Depopulation of the Mn2+ state in ZnO:Mn upon illumination, monitored byquenching of the Mn2+ EPR signal intensity, was observed at temperaturesbelow 80 K. Mn2+ photoquenching is shown to result from the Mn2+ → Mn3+ionization transition, promoting one electron to the conduction band.Temperature dependence of this process indicates the existence of anenergy barrier for electron recapture of the order of 1 meV.GGA+U calculations show that after ionization of Mn2+ a moderate breathinglattice relaxation in the 3+ charge state occurs, which increases energiesof d(Mn) levels. At its equilibrium atomic configuration, Mn3+ ismetastable since the direct capture of photoelectron is not possible. Themetastability is mainly driven by the strong intra-shell Coulomb repulsionbetween d(Mn) electrons. Both the estimated barrier for electron captureand the photoionization energy are in good agreement with the experimentalvalues.