Electroluminescence efficiency profiles of Mn in ZnS ac thin-film electroluminescence devices

We report a direct measurement of relative Mn electroluminescence (EL) efficiency in an ac EL device as a function of position normal to the ZnS film plane. The Mn EL efficiency decreases strongly with distance from the cathodic to anodic region of the ZnS layer. The cathodic-to-anodic efficiency ratio is about two orders of magnitude. In addition, the first ∼0.2 μm of ZnS deposited exhibits a significantly lower Mn EL efficiency relative to the remaining ZnS.