GB804764A - Improvements in x-ray screens - Google Patents

Abstract

804,764. Electroluminiscent materials : image intensifiers. GENERAL ELECTRIC CO. Aug 23, 1956 [Sept. 12, 1955], No. 25808/56. Class 39(1). An X-ray image intensifier comprises a layer of X-ray sensitive material having a characteristic visible light emission when excited by X-rays, and a visible light amplifying cell having a peak sensitivity to that characteristic emission, contiguous with the X-ray sensitive layer means being provided to impress an electrical potential difference between opposite surfaces of the light amplifying cell. The light amplifying cell, Fig. 2, comprises a continuous homogeneous, non- particulate layer 5 of visible light-sensitive visible light emitting material sensitive to a short wavelength blue light characteristic of the X-ray sensitive layer 4, the potential difference being impressed by transparent conducting layers 6, 7. The X-ray sensitive layers 4 may be of calcium tungstate or of zinc and/or cadmium sulphides with a Zn to Cd ratio of 3 to 1 or with Cd as 15À35 per cent. of the sulphide, activated by 0À001 to 0À3 per cent of silver with chlorine. One such mixture has a peak emission when excited at 5100‹A. The light sensitive, light emitting layer 5 may be composed of a zinc and cadmium sulphide comprising 0À70 per cent. Zn, remainder Cd, a zinc sulpho-selenide comprising 0À70 per cent. S, remainder Se, 0À5 to 2 per cent. Mn and 0À001 to 0À3 per cent. Cl, I, In or Ga. The electrode layers 6, 7 are of titanium dioxide. In forming the cell shown in Fig. 2, the plate 8 is first treated at 200‹C with vapours of titanium tetrachloride and water to form the layer 7 and is then subjected to the vapours of a charge containing zinc, zinc iodide and manganese iodide at 750‹C in an atmosphere of hyrdogen sulphide and/or hydrogen selenide to deposit the layer 5. Thereafter the initial process is repeated to form the second titanium dioxide layer 6 and finally sprayed with the X-ray sensitive material 4 in a suitable nitrocellulose or potassium silicate binder. Finally the whole plate assembly is baked for about one hour at the temperature necessary to thermally set the binder. Suitable thicknesses of the various layers are specified. Specification 724,977 is referred to.