Mn²⁺ EPR characterization of thin film electroluminescent devices

The manganese luminescenct center in ZnS:Mn powder and thin films have been investigated as a function of Mn concentration using EPR spectrometer. While the concentration of the isolated Mn²⁺ ions decreases with increasing Mn concentration, the concentration of the Mn clusters increases. It is turned out that the proper Mn concentration for a good ZnS:Mn ELD is about 0.5 mole%. At high Mn concentrations, where the ZnS powder has a dominant hexagonal phase, the Mn ion still prefers to substitute for Zn in ZnS:Mn at the cubic site rather than at the hexagonal site. The isolated Mn²⁺ ions seem to be changed to monovalent Mn¹⁺ after aging of ZnS:Mn ELD.