CXXI. The electrical properties of electroluminescent phosphors

Summary Measurements have been made of the dielectric properties of a number of electroluminescent phosphors in the form of powders and polycrystalline lumps. There appear to be two quite separate mechanisms giving rise to dispersion: one which is present in the dark and the other which is stimulated by irradiating the phosphor with ultra-violet light. The latter is very similar to the dispersion found in ordinary non-electroluminescent powders and has not been studied further. The former, which seems to be characteristic of electroluminescent phosphors, produces dispersion at very low frequencies and has been investigated in detail. Measurements have also been made of the variation of dielectric properties with voltage and with temperature. To explain the effects observed it is assumed that electronic barriers are formed in the specimen and that motion of some of the ions in the barrier region takes place. On the basis of this model it is found possible to account in a semi-quantitative manner for the experimental results. Values are deduced for the height of the barrier and for the number and diffusion coefficient of the mobile ions.