Patent GB-1312563-A (GB)
Title: Fluorescent materials for optical frequency conversion
IPC: C03C3/32
Filed: 1971-04-19
Abstract: 1312563 Glass F AUZEL 19 April 1971 [10 Feb 1970] 21767/71 Heading C1M [Also in Division C4] A fluorescent material for 0À85 to 1À06 Ám. infra-red to visible conversion comprises (a) mixtures of fluorides of Pb, Be and Mg, (b) a fluoride of Yb, (c) a fluoride of Er and/or Tm. Concentrations may be 20 to 45% lead fluoride, 20 to 40% of beryllium fluoride, 5 to 20% magnesium fluoride, and less or more than 20% of ytterbium fluoride for a glass or glass ceramic or polycrystalline structure respectively. Er and Tm doping may be 6 Î 10<SP>20</SP> to 24 Î 10<SP>20</SP> atoms/c.c. and 1À5 Î 10<SP>20</SP> to 6 Î 10<SP>20</SP> atoms/c.c. In preparation the components are mixed in a powdery state at room temperature, heated to 1200‹ C. in a muffle oven to melt, cooled from 1200‹ to 500‹ C. and cast in a mould. The mould may be heated to 100‹ C. before casting, resulting in a product of glass formation, or heated to 250‹ C. before casting and held at this temperature until solidification, to produce a ceramic material. A glass envelope surrounding a ceramic body may be produced by preheating a deep mould to 250‹ C. and allowing to cool to 100‹ C. during solidification, cooling being stopped when the periphery and inner portion of the cast is at 100‹ and 250‹ C., respectively. Moulds may be as in Figs. 1 to 3 (not shown), Fig. 1 producing rectangular or other plates, Fig. 2 mould producing planoconvex lenses of 1À37 refractive index and Fig. 3 producing a lenticular screen. To produce a crystalline powder, the product may be left to cool to room temperature in the crucible and then (a) packed between two thin parallel glass plates, (b) sedimented and coated with a synthetic resin, (c) suspended in a transparent gel. A glass ceramic body 4 0  may be surrounded by a lenticular glass body in Fig. 4, produced by the Fig. 3 mould, the glass Á being 1À37. Efficiency increases with input energy, and relationships including also emissive colours and intensity v. input radiation, are discussed. In examples. specific concentrations are given and the Be fluoride starting material may be of the form NH 4 BeF 4 . Fig. 5 (not shown) includes photoemissive diode (11), metallic base (12), Au wire (14), glass pearl (16), metal hood (17), and filter (20) adjacent the optical conversion layer. Particular emission colour-filter combinations are discussed. The converter layer may have a lenticular surface as above, and diode (11) may be at the centre of a transparent sphere. The interior of hood (17) may be filled with a translucent silicone gel which may contain grains of the fluorescent powder or a dye as an optical filter. Use with 0À97 Ám. (or 0À92 to 1 Ám.) photo-emissive diodes is instanced, a 0À90 Ám. GaAS : Si diode being disclosed and other 0À97 Ám. diodes being In(P x As 1-x ), where 0À98 < x < 1; As(Jn x Ga 1-x ) where 0À005 < x < 0À15 or Sb(Al x Ga 1-x ), where 0À37 < x < 0À74. Uses may be for illumination by signalling in telephone switchboards, automobile and aeroplane dashboards, satellite instrument panels, calculator consoles, low definition TV receivers with flat screens and infra-red detection screens.