Electrical characterization of white SrS/ZnS multilayer thin-film electroluminescent devices

Thin-film electroluminescent devices with double or triple phosphor layers are used to produce a bright white emission. With the blue emitting SrS:Cu, the blue and green emitting SrS:Ce, the green emitting ZnS:Tb, and the green and red emitting ZnS:Mn, several white emitting combinations can be obtained. The electric field and electron current in such a multilayer phosphor are often not homogeneous. Combined electrical and optical measurements show that the field at the cathodic side of the phosphor is normally larger than at the anodic side, due to positive space charge in the phosphor layer. At low applied voltages, electrons can be trapped in the multilayer before reaching the anodic insulator interface. A part of the phosphor layer is then not excited, and this disturbs the balance of colors emitted from the multilayer phosphor device. © 2000 American Institute of Physics.