Interpretation of Electroluminescence Effects in an Excited Phosphor

Abstract

The consideration of electron transitions between valence band, conduction band, and traps as presented by Randall and Wilkins' theory of luminescence growth is extended by including terms which take into account the emptying of traps by an electric field and the draining off of electrons by field-induced, non-radiative transitions. The result of the mathematical analysis corresponds to effects observed in a ZnS phosphor, embedded in a dielectric matrix, under the influence of a periodic electric field while continuously excited by ultraviolet radiation. These are a momentary illumination, an extinguishing effect, and the superposition of a ripple with twice the frequency of the field, whose amplitude decreases with increasing frequency. Some further observations are discussed qualitatively, utilizing the following assumptions: the draining effect ceases after some time; at low frequencies and for dc fields, a current effect counteracts the draining effect.