Time resolved DC electroluminescence studies in ZnS:Mn, Cu powder phosphors

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Abstract
Time resolved studies of DC electroluminescence (EL) from ZnS:Mn, Cu powder phosphors are reported. An emission band arising from the Mn2+, 4T1 to 6AI transition and a very broad band attributed to radiative interband transitions of hot electrons are detected. The hot electron band is used as a probe of the onset of avalanching in the devices. EL emission is found to occur simultaneously for the two bands. Detailed studies of the EL onsets reveal that luminescence emission occurs, to within 100 ns, when the voltage across the high resistivity region is sufficient for avalanching, without any additional delay being present. This is consistent with the Mn2+ being excited by direct impact by hot electrons. The rate of decay of the Mn luminescence is found to increase with increasing Mn concentration. Various concentration quenching mechanisms are discussed to account for this behaviour. High current densities are deduced from the rate of increase of luminescence rise transients. Only 1 to 5% of the Mn ions in the phosphor can be excited.