Electroluminescent characteristics of ZnS : Cu, Pb, phosphors excited by rectangular pulse fields which have a fast rise time, are investigated. The widths of these electric pulse fields are 200μ sec to 2 m sec with the frequencies of below 100 cps.
Especially the experiments in relation with the wave forms, decay times, voltage and temperature-dependencies regarding the light out-puts are performed.
Wave forms of the light out-puts with these fields have two peaks at the leading and trailing edges of pulse voltages, and the luminescence decays following these two peaks are simillar in shape, the decay times of which are about 100 μ sec at room temperature and about 300 μ sec at 100°C.
Wave forms of green and blue luminescence seem to be of essential difference, and the ratio of secondary to primary peaks of the green luminescence increases with temperature.
The experiments on thermoluminescence in this phosphor indicate the existence of two types electron traps, one of which has the depth of about
E=0.33 eV and the other about
E =0.47 eV. The values of these trap depths seem to correspond to the experimental values of luminescence decay times, namely the traps of
E=0.33 eV correspond to the experimental decay time at room temperature and E=0.47 eV to the decay time at 100°C.
Some speculations relating to these electroluminescent phenomena are made. It is likely that the primary electrons might be thermally generated from the surface traps and excite the luminescence centers, and the electroluminescent decay times might correspond .to the rate of generation of the primary electrons at the grain surfaces of phosphors.
Other detailed characteristics of the electroluminescent wave forms are discussed based on this consideration.
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