GB1143362A - Information recording - Google Patents

Abstract

1,143,362. Luminescent coding. AMERICAN CYANAMID CO. 8 March, 1966 [8 March, 1965], No. 10198/66. Heading G4M. [Also in Division C4] At least two luminescent substances capable of emitting radiation in discrete, predetermined and mutually different bands when illuminated with short wavelength radiation, at least one of said substances being a complex of a rare earth metal ion having an atomic number greater than 57, are applied to a substrate in a process of recording information. Preferably the active materials absorb radiation in the U.V. region and emit over different narrow regions of the visible spectrum although X-ray fluorescent materials may be used. The substances may be applied as a coating to form marks. The coated area may be pigmented or clear and may be formed or shapeless. The marks may comprise a sequence of patches (e.g. squares) in a line or a sequence of concentric circles or polygons. They may comprise a clear fluorescent coating in combination with a pigmented character. Each mark may be formed by a single coating with a substance comprising a plurality of active fluorescent materials mixed together or by successive coatings of substances comprising single active materials. In an example, each mark represents a decimal digit according to which of four possible different active materials are present. Other examples refer to the use of six and ten active materials. The ternary rather than the binary system of coding may be adapted if used with a reading device which can distinguish two levels of presence. The marks may be applied for example to cheques, price tags or sacks. The single figure (not shown) illustrates a reading device comprising a quartz U.V. lamp (2), focusing and collimating lenses (3, 5, 7), aperture (4), dispersing element (6) and photomultiplier tubes (8-11) for detecting the presence or absence of four characteristic emitted wavelengths. The reader may be fixed and the documents (12) movable or vice versa or both may be stationary if the reader includes a scanning arrangement such as a movable lamp or pivoted mirror. The dispersing element may comprise a prism or diffraction grating or may be replaced by dichroic mirrors or narrow bandpass filters. The photomultiplier tubes may be replaced by suitable solid state photo-conductive or photo-voltaic devices. Materials referred to as being most suitable are rare earth complexes involving organic chelating ligands (preferably beta-diketones, ortho-hydroxy aromatic ketones or 2,21-bipyridine) with or without synergic agents such as a trialkyl phosphine oxide. Diphenylanthracene is also a suitable material. Rare earths mentioned, together with characteristic wavelengths, are as follows: Pr (0À65Á or 1À047Á), Nd (1À06Á), Sm (0À645Á), Eu (0À613Á), Tb (0À543Á), Dy (0À576Á), Yb (0À971Á), Er (1À54Á) and Tm (1À8Á). Examples are given of suitable film forming compositions including fluorescent materials.