Color eletroluminescence from ZnS thin films multi-doped with rare-earth ions

The electroluminescence (EL) cell is made from thin films formed by the co-evaporation of ZnS and rare-earth metals. The radiation from this cell is caused by electron transitions between the levels of rare-earth ions. In this study we determine the relationship between the concentration of the rare-earth ions and the luminous spectral intensity in the EL cell and the applied voltage. The luminescence center of rare-earth ions in ZnS is localized center. If the ZnS is activated by two different rare-earth ions then the resultant emission color is the sum of two individual emission colors. Thus the emission color can be changed, as desired by controlling the concentrations of rare-earth ions. On the other hand it is observed that the spectrum of an EL cell containing several kinds of rare-earth ions changes when the applied voltage changes.