Modeling of electron transport and luminance in SrS:Cu,Ag ACTFEL display devices

Transient and steady state responses of luminance and current in SrS:Cu,Ag ac thin film electroluminescent (ACTPEL) display devices were measured and analyzed. The results indicated the importance of bulk space charge, which was attributed to ionized activators in the bulk phosphor layer. For dented voltage pulse excitation, four luminance peaks were observed. These were labeled as the leading edge (LE) peak, dent peak, beginning of trailing edge (BTE) peak and the middle of trailing edge (MTE) peak. Ionized activators play an important role not only in affecting the net phosphor field but also in the device luminance during the trailing as well as the leading edges of the voltage pulse. It is shown that the dent peak and the BTE are due to a bulk recombination process instead of the backflow from the anodic interface. The luminance behavior of the device can be understood in terms of the bulk dipoles in the phosphor layer. A bulk dipole consists of a positively charged ionized Cu activator and a “daughter” trap (negatively charged) in its vicinity. A physical model for various optoelectronic processes is presented. The model can explain experimental data in a qualitative fashion