Luminescent impurity doping trends in alternating-current thin-film electroluminescent phosphors

The doping properties of three alternating-current thin-film electroluminescent (ACTFEL) phosphor host/luminescent impurity systems, ZnS:Mn, SrS:Ce, and SrS:Cu, are elucidated, and the ACTFEL device implications of these properties are assessed. Mn is isovalent, Ce is a donor, and Cu is an acceptor. Moreover, Ce is readily ionized in SrS, so that it behaves as a double donor. The distinctly different doping nature of these three luminescent impurities leads to dramatically disparate defect and device physics trends. The donor/acceptor nature of Ce/Cu in SrS results in charge neutrality being achieved in SrS:Ce and SrS:Cu via self-compensation-induced vacancy creation; subsequent defect complexing between oppositely charged luminescent impurities and self-compensation-induced vacancies results in more complex ACTFEL device behaviors such as dynamic space charge, trailing-edge emission, charge collapse, color tuning, and electroluminescence (EL) thermal quenching. In contrast, the isovalent nature of ZnS:Mn leads to more ideal ACTFEL device operation. This suggests that the optimal ACTFEL phosphor luminescent impurity is isovalent.