Patent GB-1214222-A (GB)
Title: Luminescent memory and display devices
IPC: H05B33/00
Filed: 1968-04-22
Abstract: 1,214,222. Electroluminescence. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 22 April, 1968 [2 May, 1967], No. 18968/68. Heading C4S. A luminescent memory and display device comprises an element 10 having e.1. material in a dielectric substrate which maintains a residual component of electric field when an applied D.C. external field is removed, means 7, 8 for applying two D.C. potentials of mutually opposite polarity V B1 , V B2  and an A.C. potential V A  across the element. Applying V B2  for a short time before exciting the e.1. material with V A  polarizes the dielectric and reduces the luminescent output depending on the magnitude of V B2 . Applying V B  removes or reduces this effect and either returns the output to its original value or to an intermediate value, resulting in erasure or control of the output. Polarization is a function of time up to a saturation value hence control depends on the product of time and V B1  or V B2 . The A.C. potential can be applied together with the D.C. potentials to monitor the result as V A  does not effect polarization. V A  produces two sets of luminous pulses of different intensity, Fig. 2A (not shown) corresponding to peak and trough voltages. An electric motor 11  synchronous with V A  drives a rotary disc light chopper 12 to exclude light of lower intensity. The element comprises Cu or A1 activated ZnS dispersed in liquid tricresyl phosphate between tin oxide electrodes 2, 3 deposited on glass plates 4, 5 with an insulating polyester spacer 6. Another element is formed by applying a powder mixture of boron-silica frit containing Li and/or Ti, ZnS e.1. material and a light reflective high resistance oxide of Sn, Ti or Sb to a glass, metal or ceramic plate and heating to fuse the frit. An X-ray image is stored and displayed in the embodiment of Fig. 4 in which the element comprises a glass substrate, electrode 15, e.1. layer 1 opaque layer of carbon in a binder or black pigment and glass enamel 16, a p.c. layer 17 of CdS and/or CdSe sensitive to light and X-rays in a plastics material or glass, a Au electrode 18, a layer 19 of powdered e.1. material ZnS or ZnSe and X-ray fluorescent material ZnCdS in a binder and a light reflecting Al foil electrode 20. A polarized field pattern corresponding to an incident X-ray image is produced by brief exposure to the image with V B2  applied. The X-rays and corresponding light image formed in layer 19 affect the p.c. layer 17 resulting in a D.C. voltage pattern which produces a polarization pattern and a reverse light image is then produced by V A . The magnitude of V A  can be reduced by applying V B  causing light emission from layer 19 which reduces the impedance of the p.c. layer uniformly. The image is erased by applying V B1  and V E . A positive image can be formed by applying V B2  uniformly and V B1  instead of V B2  with exposure to the X-ray image in either sequence. In another embodiment the element is mounted in a C.R.T. and information is written in by the electron gun. The electrode facing the gun is in the form of a grid and secondary electron emitting MgO is added to layer 1 to increase sensitivity. An image can be produced as above or the information in the form of a potential can be obtained by rescanning. Radiation induced ionization piezoelectric and photo-electron emitting means for writing in information are referred to.