Electroluminescence under Pulsed Square Wave Excitation

Abstract

The slow return of an electroluminescent cell to its equilibrium state following a field excitation has been studied for a blue‐green emitting phosphor and for a yellow‐emitting phosphor. The light pulse emitted upon the rise of a square voltage pulse was measured as a function of repetition rate and of temperature between −130° and 150°C. Relaxation times encountered varied between 10−2 sec and 105 sec. The temperature dependence of the relaxation rate exhibits effective activation energies of about 0.4, 0.7, and 0.6 ev, respectively, for the blue, green, and yellow emission bands. The results do not seem to favor the mechanism of delayed recombination. An alternative mechanism is suggested whereby the number of filled deep donors is assumed to control the electroluminescence emission via the number of field‐ ionizable electrons available for collision‐excitation of centers. Observations were also made on some other effects associated with square wave excitation.