Patent GB-980452-A (GB)
Title: Improvements in or relating to electro-luminescent devices
IPC: H05B33/26
Filed: 1960-09-02
Abstract: <PICT:0980452/C4-C5/1> <PICT:0980452/C4-C5/2> <PICT:0980452/C4-C5/3> <PICT:0980452/C4-C5/4> <PICT:0980452/C4-C5/5> Electroluminescent device, particularly for indicating variable physical quantities, or for advertising, comprises an electroluminescent member and two electrodes for applying a voltage across the member, electric connection between at least one of the electrodes and at least a part of the member subsisting through a fluid across a variable contact area.  In the construction shown in Fig. 1 for indicating the level of mercury 4 in a tube 1, which can be a measure of temperature or pressure, an electroluminescent layer 2 of ZnS : Cu, Al and a transparent conductive electrode 3 of tin oxide are provided, the second electrode being in contact with the mercury.  The tube 1 can consist of a barium-calcium titanate-zirconate having a mol. percentage composition of BaO-44, CaO-4, TiO2-44 and ZrO2-8.  In the construction shown in Fig. 2 a tube 11, as above, containing mercury 17 carries three layers 13, 14, 15 of electroluminescent material, each having a different emission wavelength, the layer 13 consisting of ZnS : Cu, Al giving green luminescence, the layer 14 consisting of ZnS : Cu, Cl giving blue luminescence and the layer 15 consisting of ZnSe : Cu, Al giving red luminescence.  The layers 13, 14, 15 are covered with a transparent conductive electrode 16 of tin oxide, and to improve transverse conductivity a part of the electrode 16 is covered with a tape-shaped silver conductor 18 extending lenghtwise of the tube 11.  In the construction shown in Fig. 4 a tube 31 having a lower part 32 of glass and an upper part 33 of barium-calcium titanate-zirconate is partly covered on the inside with an electroluminescent layer 34 covered with a transparent tin oxide electrode 35 connected to a metal layer 36 connected to a voltage source.  The tube 31 is rigidly positioned in a conductive fluid 37, e.g. an aqueous salt solution, in contact with a second electrode. An indication element 38 connected to conductors 39, 40 is provided in the tube 31 at the same level as the layer 34, the element 38 being sensitive to the radiation emitted by the layer 34 when the level of the fluid 37 is above a fixed height. Fig. 6 shows container 50 with opaque walls except for a transparent area 51 of barium titanate.  Discrete indicia portions 52 of the area 51 are covered with electroluminescent material, and the area 51 including the portions 52 are covered with a transparent tin oxide electrode 53.  A lead 54 from a voltage supply is connected to the electrode 53, and a lead 56 passing into the container 50 contacts a conductive liquid, e.g. a salt solution.  The container 50 has a supply pipe 57 and an outlet pipe 58 for the liquid, and feed and withdrawal of such may be controlled in dependence on the height of the liquid.  In the construction shown in Fig. 7, a metal electrode rod 71 carrying an electroluminescent layer 72 is positioned within a glass tube 70 containing a conductive transparent fluid 73, e.g. a salt solution, in contact with a second electrode.  Dielectrically conductive fluids such as nitrobenzene and methanol can be used instead of mercury or a salt solution.  The tubes used can be of material having a dielectric constant of at least 20, e.g. ceramic dielectrics on a basis of titanium dioxide or of metatitanates having the Perowskite structure or mixed crystals thereof. Preferably the tubes, at least where coated with electroluminescent material, consist substantially of a compound having the formula ARO3, in which H is at least one of the metals Ba, Sr, Pb and Ca, and R at least one of the metals Ti, Zr and Sn, which materials have a coefficient of thermal expansion approximately that of glass.  The electroluminescent layer may comprise a plurality of components which may be contiguous or physically separate, and the components may differ in respect of emission intensities and/or emission wavelengths.