The Light Waveforms Emitted from Electroluminescent Cells Energized by Square Waves and Pulses of Voltage†

Abstract

ABSTRACT Light pulses which rise to a maximum in less than 0-2 μs can be obtained from electroluminescent cells excited by voltage waveforms with fast edges. The pulses decay more slowly, taking from 2 to 3 μs at a PRF of 50 kc/s and about 100 μs at 200 c/s, to decay to one-third of the maximum amplitude. The dependence of this maximum amplitude on the peak value of the voltage obeys a similar law to that already found for the average brightness of a cell. These and other features of the light pulses depend on the time-variation of the electric field strength within the phosphor crystal. The waveform of the electric field is quite different from the applied voltage and can be regarded as having two components due respectively to the applied voltage and the internal space charge which is built up during the first few cycles of excitation. The former can be found approximately from a simplified equivalent circuit, and information about the latter can be obtained from a consideration of the part played by electron traps in the mechanism of electroluminescence.