Patent GB-952630-A (GB)
Title: Method of forming thin films of luminescent material and product resulting therefrom
IPC: C23C14/06
Filed: 1960-08-15
Abstract: Method of producing a thin, light-transmitting film of electro-luminescent, photo-luminescent or cathodo-luminescent material on a substrate comprises evaporating on to the substrate a thin film of at least the matrix of the luminescent material, placing about and in contact with the formed film a finely divided material comprising substantially the matrix and the activator, firing the assembly to render the formed film luminescent and separating the luminescent film from residual finely-divided contacting material. The contacting material can consist of the luminescent material in finely-divided form.  Firing can take place at a temperature, e.g. at least 700 DEG  C., of at least 70% of the firing temperature normally used in making the luminescent material in finely divided form and the substrate is so supported during firing that it will not deform if its softening temperature is exceeded. The luminescent material can be electroluminescent zinc sulphide activated by copper and coactivated by a halogen and the substrate can be glass carrying a light-transmitting electrically-conducting layer of tin oxide, the glass having specified coefficients of linear thermal expansion.  The formed film can be washed in a solution which removes any excess copper from the film e.g. aqueous solutions of alkali cyanides, thiocyanates or thiosulphates, particularly a water solution containing 10% by weight of sodium cyanide and 5% of sodium hydroxide.  Phosphors also referred to are ZnS, activated by Cu and Mn and coactivated by Cl, ZnS activated by Cu and/or Mn or Ag, ZnS.CdS activated by Cu or Ag, MgO.MgF2.GeO2 activated by Mn Zn2SiO4 activated by Mn, ZnO activated by Zn, Zn3(PO4)2 activated by Mn, and 4500 DEG  K. halophosphate. The phosphors can be prepared as described in Specification 863,107.  Apparatus for forming the phosphor film is described. Electroluminescent phosphors formed on the glass-tin oxide substrate as above can be covered by a vacuum-metallized aluminium electrode to form an electroluminescent cell which can be energized by A.C. or D.C. with either electrode positive.  In another construction a thin film of a material with a high dielectric constant, e.g. barium titanate or titania, is first formed on an electrode substrate followed by layers of phosphor, tin oxide and glass.  In another construction the phosphor film is formed on a wire-mesh electrode carried by a glass substrate and is covered by a layer of powdered barium titanate mixed with a small amount of glass or plastic dielectric material such as polyvinyl chloride covered by an aluminium electrode layer.  In other constructions thin films of different phosphors can be superimposed on one another with or without the interposition of a layer of high dielectric constant material.  The phosphor films can also be formed on the face-plate of cathode-ray tubes or used in cathodo-luminescent lamps being excited by low voltage electrons from a tungsten filament or other source. Specification 789,078 also is referred to in this connection.ALSO:Apparatus for coating an inorganic substrate 24, such as glass, with at least the matrix 40 of a phosphor material by evaporation comprises a bell-jar 12 supported on a non-conducting foundation 12 through which is sealed an evacuating tube 16.  A spider 18 supports a shaft 20 and a plate 22 holding the substrate 24. The shaft is rotated by a motor 26 and magnetic coupling 28.  The material to be evaporated is contained within a tantalum boat 30 <PICT:0952630/C3/1> supported by electrodes 32 connected with a rheostat 34, ammeter 36 and an A.C. source. The material is retained within the boat 30 by a tungsten wire 38.  The substrate 24 can be glass having a coefficient of linear expansion of about 64 X 10-7 per degree C. and if the phosphor is electrolumnescent the substrate carries a thin layer 37 of light-transmitting, conducting material such as tin oxide for forming an electrode.  The bell jar 12 is evacuated to a pressure of about 10-4 mm. and the boat 30 is heated rapidly to a temperature of from 1200-2000  DEG C., preferably 1200-1400  DEG C. The temperature of the substrate 24 during evaporation can vary from room temperature up to just below the temperature that would cause the film 40 to be re-evaporated or to cause the substrate 24 to soften.  The material in the boat 30 can be pure matrix of the phosphor or the activated phosphor, such as zinc sulphide activated by copper and co-activated by a halogen, in which case some activator and co-activator may be evaporated on to the substrate 24 as well as the host material zinc sulphide.  Phosphors also referred to are ZnS activated by Cu and Mn and co-activated by Cl, ZnS activated by Cu and/or Mn or Ag, ZnS.CdS activated by Cu or Ag, MgO.MgF2.GeO2 activated by Mn, Zn2SiO4 activated by Mn, ZnO activated by Zn, Zn3(PO4)2 activated by Mn, and 4500  DEG K halophosphate. The formed film can be washed in a solution which removes any excess copper from the film, e.g. aqueous solutions of alkali cyanides, thiocyanates or thiosulphates, particularly a water solution containing 10% by weight of sodium cyanide and 5% of sodium hydroxide. Specifications 789,078 and 803,107 are referred to.