Optical Properties of Manganese Doped Wide Band Gap ZnS and ZnO
  Optical properties of ZnMnO layers grown at low temperature by Atomic Layer Deposition and Metalorganic Vapor Phase Epitaxy are discussed and compared to results obtained for ZnMnS samples. Present results suggest a double valence of Mn ions in ZnO lattice. Strong absorption, with onset at about 2.1 eV, is tentatively related to Mn 2+ to 3+ photoionization. Mechanism of emission deactivation in ZnMnO is discussed and is explained by the processes following the assumed Mn 2+ to 3+ recharging. 
M. Godlewski, A. Wojcik-Glodowska, E. Guziewicz, S. Yatsunenko, A.   Zakrzewski, Y. Dumont, E. Chikoidze, M.R. Phillips
cond-mat.mtrl-sci