Study of emission efficiency in ac driven light emitter devices

A study of the high field emission efficiency in ZnS:Mn is presented. At intense electric field conditions the band bending resulting from space charge effects has not been considered since the space charge density in the active layer is low. We demonstrate that ac driven TFEL devices with large insulator capacitance and no space charge effects in the active layer are optimal in terms of providing the energy transfer from sensitizers to luminescent centers. The analysis takes into account the pair-producing mechanism by direct electron impact with a characteristic electron energy distribution described by the Wolff distribution function. From the described model for a typical structure, the emission efficiency behavior could be expressed by the relation between the minimum distances required by the emitted carriers to produce electron-hole pairs and ac drive conditions.