A hysteresis effect in photoconductive cadmium selenide and its use in a solid-state image storage device

A brief description of a new hysteresis effect in cadmium selenide photoconductive powder will be given. Photocurrent plotted as a function of voltage has the form of a hysteresis loop, with triggering from low to high currents occurring at a voltage depending on the incident light level. At a suitably chosen voltage, triggering from low to high currents occurs with light pulse excitation. Return to the condition of low current flow is brought about by brief interruption of the supply voltage. Since the triggering is present with ac or dc operation, it is possible to use the effect in a series circuit of photoconductor and ac operated electroluminescent panel. If this is done on an area basis with due attention paid to the impedance match of the photoconductor and electroluminescent layer, it is possible to make an image storage device having no optical feedback. The construction and operation of such a device is described, and a photograph of a stored image on a 3-inch panel is shown.