Impact Excitation Cross Section in Electroluminescence
Recombination radiation and luminescence from discrete centers appear to have different characteristics. In general, the lifetime of recombination radiation is much shorter than that of luminescence from discrete centers. The concentration of discrete centers is also limited. Before 1970, the phosphor of electroluminescence (EL) was mainly in the form of powder. The recombination through impurities, e.g. Cu+, was preferred. After 1974, thin film and discrete center were preferred, e.g. Mn+.? But the saturation of EL is often observable. And the reported highest energy efficiency is obtained for samples which is designed to guarantee the ultimate return of free electrons to the region of ionized centers. The direct impact excitation is believed to be the machanism of excitation of the luminescent centers in the phosphor. Hence, the impact cross section is a very important parameter for the excitation process. It reflects the excitation probability of the luminescent center, and has been investigated both theoretically and experimentally /1, 2, 3, 4/. Most of the results are rather rough and the variation of impact cross section with hot electron energy is not clear. In this paper, by means of the simple but effective method developed by CHEW /5/ and subsequently used by AKERIB and BOROWITZ /6/ in their study of inelastic scattering problem, we investigated the impact cross section σ and the variation of σ with hot electron energy. And taking ZnS:Mn (discrete center) and ZnS:Cu (recombination center) as examples, we performed the numerical calculation.
KeywordsConduction Band Recombination Radiation Luminescent Center High Energy Efficiency Impact Excitation
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