Title of Invention

SECURITY DOCUMENT AND SECURITY ELEMENT

Abstract

Security document, with at least one authentication mark in the form of a luminescent substance, comprising a substrate material supporting said luminescent substance, wherein the luminescent substance is based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible region of the spectrum, is excitable in substantial parts of the visible region of the spectrum and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 µm, wherein the rare earth metal emits in the wavelength range between 0.8 and 1.1 µm, and the host lattice has a garnet of perovskite structure.

Full Text

SECURITY DOCUMENT AND SECURITY ELEMENT FIELD OF THE INVENTION The present invention concerns a printed valuable document such as a security document with at least one authentication mark in the form of a luminescent substance based on a host lattice doped with at least one rare earth metal. The protection of valuable documents by means of luminescent substances has been known for a long time. The use of rare earth metals in this connection has also been discussed. These have the advantage of possessing, in the infra-red spectral region, narrow-band emission lines, which are particularly characteristic, and can therefore be safely distinguished from the emissions of other substances when using measuring technology. In order to increase protection against counterfeiting still further, the rare earth metals can be incorporated together with other substances in host lattices, with the result that the excitation and/or emission spectrum of the rare earth metal is influenced in a characteristic manner. By combination with suitably absorptive substances, tor example, a part of the excitation and/or emission bands of the rare earth metal can be suppressed. This influence can. however, also take the form of a "distortion". e.g. through damping of specific regions of broad-band spectra. Likewise for reasons of protection against counterfeiting, rare earth metals with emission lines above 1500 nm are frequently used, since detection of the emission becomes more elaborate and more difficult the further into the IR spectral region the emission lines lie, For in very general terms, the principle applies that the detection sensitivity of photodetectors decreases the longer the wavelength of the radiation to be measured, since the signal-to-noise ratio becomes smaller in the same proportion; i.e. the signals to be detected are more and more difficult to identify in the noise. The luminescent substances must therefore also be present in the valuable document in a certain minimum concentration, in order to be able, to produce an adequate signal strength, which can be reliably detected in the noise. In certain instances, however, these limit concentrations necessary for detection cannot be produced; for example, if the luminescent substances have their own colour, which destroys the desired colour impression when mixed with the material of the valuable document. In some cases, the attempt is also made to reduce the risk of detection by chemical analysis of the luminescent substances contained in a valuable document by the fact that the luminescent substances are applied only in very small concentrations. In such cases, luminescent substances must be avoided for which the emission lines can be readily detected even in small concentrations. The invention is therefore based on the aim of providing a valuable document with a luminescent substance producing emissions in the near IR spectral region so that, even at low concentrations, the presence of the luminescent substance can be demonstrated in the valuable document. Accordingly, the present invention provides a security document, with at least one authentication mark in the form of a luminescent substance, comprising a substrate material supporting said luminescent substance, wherein the luminescent substance is based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible region of the spectrum, is excitable in substantial parts of the visible region of the spectrum and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 urn, wherein the rare earth metal emits in the wavelength range between 0.8 and 1.1 urn, and the host lattice has a garnet of perovskite structure. Preferably, the rare earth metal is ytterbium, praseodymium, or neodymium. Preferably, the host lattice contains chromium as the absorptive component. The garnet structure can be described by the general formula A3Cr5.xAlxO12, where AD stands for an element from the group of scandium, yttrium, the lanthanides, the actinides, and the index x fulfills the condition 0 luminescent substance can be described by the formula Y3. 2DzCr5. x AlxO12, where D stands for an element from the group of neodymium, praseodymium, or ytterbium, and the index z fulfills the condition 0 the general formula ACrO3, where A stands for an element from the group of yttrium, scandium, or the lanthanides. The luminescent substance can be described according to the formula Y1 . zDzCrO3, where D stands for an element from the group of neodymium, praseodymium, or ytterbium, and the index z fulfills the condition 0 Preferably, the luminescent substance is mixed into a printing ink, which additionally contains visible colour additives or the luminescent substance is mixed into the paper pulp. Preferably, the luminescent substance is provided on or in said substrate material, which is at least partially embedded in the paper pulp. The substrate material may consist of plastic or may take the form of a security thread or mottling fibre. The luminescent substance is provided as an invisible and at least partial coating on the substrate material. Tthe coating takes the form of a stripe. The luminescent substance may be provided in the volume of the substrate material. The luminescent substance is present in the substrate material in a concentration between 0.01 and 10% by weight, and preferably between 0.1 and 5% by weight. The luminescent substance is present in a layer applied to the substrate material. The luminescent substance is preferably present in a printing ink in a concentration between 0.5 and 40% by weight, and preferably between 20 and 30% by weight. The substrate material may consist of plastic or paper. The substrate material may take the form of a security thread, mottling fibre, planchet, or label. The present invention also provides a security element, which features at least one substrate material supporting and one luminescent substance based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible spectral region, is excitable in substantial parts of the visible spectral region, and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 urn, whereby the rare earth metal emits in the wavelength range between 0.8 and 1.1 urn, and the host lattice has a garnet of perovskite structure. Preferably, the luminescent substance is provided in the volume of the substrate material. The luminescent substance is present in the substrate material in a concentration between 0.01 and 10% by weight, and preferably between 0.1 and 5% by weight. The luminescent substance is present in a layer applied to the substrate material. The luminescent substance is present in a printing ink in a concentration between 0.5 and 40% by weight, and preferably between 20 and 30% by weight. The substrate material may consist of plastic or paper. The substrate material may take the form of a security thread, mottling fibre, planchet, or label. The valuable document according ro the invention contains at least one luminescent substance based on host lattices doped with rare earth metal, such that the rare earth metal emits in the near IR spectral region, i.e. in the wavelength range of between O.S µm and. 1.1 µm. This emission range has the advantage that its existence can be readily detected with a silicon (Si), gallium arsenide (GaAs), gallium-indium-arsenide (Ga,Jn,.,As) or germanium (Ge) photodetector, since these have a relatively high response sensitivity in this wavelength region. As optically active rare earth metals, consideration may be given to the elements ytterbium, neodymium. or praseodymium, or mixtures of these elements with one or more other rare earth metals. These rare earth metals are embedded in a host lattice, which has effective excitation bands in the visible region of the spectrum, and transfers these excitation bands to the rare earth metals. The effective excitation bands can be realised by. for example, chromium structural elements which, according to the invention, are incorporated in a garnet or perovskite structure. Tn this situation, the host lattice possesses an optical window in the near infrared spectral region, and absorbs in virtually the entire visible region of the spectrum, so that all the lines in the visible spectral region of the luminescent substance are suppressed. The excitation range of the luminescent substances overlaps the radiation range of strong light sources, such as halogen lamps, flash lamps, and similar sources. As a result of this, and due to the effective energy transfer to the rare earth metals within the host lattice, it is possible to use very small quantities of substance with the valuable documents according to the invention, without the automatic detection capability being restricted. Detection by means of chemical analysis, however, is rendered extremely difficult due to the low concentration. The ahsorptive constituents of the host lattice may in part be replaced by non- absorptive aluminium. The absorption, and therefore the brightness of the luminescent substance, can be controlled through the proportion of aluminium. Luminescent substances of this type cau therefore also be used as additives for lighter printing inks. Further embodiments and advantages of the invention are explained hereinafter on the basis of the accompanying drawings: Fig. 1 Excitation spectrum of a chromium-containing lattice according to the invention Fig. 2 Spectra of several light sources Fig. 3 Emission spectrum of a luminescent substance according to the invention, doped with Pr Fig. 4 Emission spectrum of a luminescent substance according to the invention, doped with Nd Fig. 5 Emission spectrum of a luminescent substance according to the invention, doped with Yb Fig. 6 Security element according to the invention, in a cross-sectional view Fig. 1 shows the excitation spectrum of a chromium-containing lattice according to the invention. This lattice absorbs in almost the entire visible spectral region. Due to this very broad-band absorption of the host lattice, the lines produced in this region by the rare earth metal dopings are suppressed. At the same tune, an energy transfer from the lattice to the rare earth doping takes place, thereby inducing the emission by the luminescent substance. The broadband absorption of the lattice also has the advantage that strong light sources can be used for the excitation of the luminescent substances, such as flash lamps, which likewise emit radiation in the entire visible region of the spectrum. Fig. 2 shows the spectrum of such a flash lamp with the reference character 1. The spectrum 1 of the flash lamp shown extends continuously from the UV spectral region into the IR region. In some cases, it may also be a good idea to illuminate the luminescent substance only with light from the visible spectrum range. In this case, illumination with light-emitting diodes offers the appropriate wavelength. Light- emitting diodes feature in general a narrow-band spectrum so that, to cover the entire spectral range, several LEDs are required. Fig. 2 shows the spectra 2, 3, 4 of a green, orange, and red light-emitting diode. Figs. 3, 4 and 5 show the emission spectra of individual luminescent substances according to the invention, Fig. 3 shows the emission spectrum of a host lattice doped with Pr. The spectrum extends from about 0.9 µm to about 1.08 urn. It features a very characteristic number of emission peaks, which can be assessed very satisfactorily as authentication features. Fig. 4 shows the characteristic spectrum of a lattice doped with Nd. This spectrum features two relatively strong emission peaks in the range from about 0.9 µm to just under 1.1 µm. A somewhat smaller peak is additionally located in the region of 0.95 The spectrum shown in Fig. 5 of a Yd-doped lattice is, by contrast, very symmetrical and shows only one peak, the maximum of which is at 1.0 urn. All these Iarrices according to the invention have the factor in common that they show a very striking luminescence emission in the near infrared region, i.e. in the range between 0.8 µm and 1.1 µm, which is difficult to identify. Although all three emission spectra are arranged in the same spectral region, they differ from one another so unambiguously that differentiation with measuring equipment is readily possible. In order to guarantee the highest possible effectiveness of the rare earth metals, in the case of a garnet structuie, host lattices are used with the general formula: A3Cr5-xAlxO12 where A stands for an element from the group of scandium, yttrium, the lanthanides, and the actinides, and the index x fulfils the condition 0 index x moves in the range between 0.3 and 2.5. A preferred embodiment of the luminescent substance according to the invention is: Y3-2.D2Cr5-xAlxO12 where D srands for neodymium, praseodymium, or ytterbium, and the index z fulfils the condition 0 If the host lattice has a perovskite structure, it can be described by the general formula: ACrO3 where A stands for an element from the group of yttrium, scandium, and the lanthanides. A preferred embodiment of the luminescence substance according to the invention is a perovskite structure can be described by the following formula: Y1-XD2CrO3 where D stands for one of the elements neodymium, praseodymium, or ytterbium, and the index z fulfils the condition 0 A number of examples of the luminescent substances according to the invention are explained in greater detail below. Example 1 Manufacture of neodymium-activated yttrium-aluminium-chromium mixed garnet (Y2.95Nd0.05Cr4Al1O12): 47.82 g yttrium oxide (Y2O3), 7.32 g aluminium oxide (AI2O3), 43.65 g chromium (III) oxide (Cr2O3), 1.21 g neodyniium oxide (Nd2O3), and 100 g dehydrated sodium sulphate (Na2CO4) are mixed intimately and heated to 1100° C in a corundum crucible for 12 hours. After cooling, the reaction product is ground, the fluxing agent is washed out wirh water, the sodium chromate produced as a side-product is reduced with sulphuric acid/iron (II) sulphate to chromium (III) sulphate, and then dried in air at 100 °C. To achieve the finest possible grain size, the powder is then ground in a stirring ball mill in water until an average grain size of less than 1 µm results. After filtration and drying, a green powder is obtained. Example 2 Manufacture of ytterbium-activated ymium-alumiiuum-chromium mixed garnet (Y2.7Yb0.3Cr3AI2O12): 43.93 g of yttrium oxide (Y2O3), 14.69 g aluminium oxide (Al2O3), 32,86 g chromihunm (III) oxide (Cr2O3), 8.52 g ytterbium oxide (Yb2O3) and 100 g dehydrated sodium sulphate (Na2SO4) are intimately mixed and heated to 1100 °C in a corundum crucible for 12 hours. After cooling, the reaction product is ground, the fluxing agent is washed out with water, the sodium chromate produced as a side-product is reduced with sulphuric acid/iron (II) sulphate to chromium (III) sulphate, and dried in air at 100 °C To achieve the finest possible grain size, the powder is then ground accordingly in water in a stirring ball mill. After filtering and drying a green powder is obtained, with an average grain size of less than 1 urn. Example 3 Manufacture of praseodymium-activated yttrium-aluminium-cliiomium mixed garnet (y2.008Pr0.02Cr2.4Al2.6O12): 51.39 g yttrium oxide (Y,O3), 20.24 g aluminium oxide (A12O3). 27.86 g chromium (III) oxide (Cr2O3), 0.5 g praseodymium oxide (Pr2O3) and 100 g dehydrated sodium sulphate (Na2SO4) ate intimately mixed and heated to 1100 °C in a corundum crucible for 12 hours. After cooling, the reaction product is ground, the fluxing agent is washed out with water, the sodium chromate produced as a side-product is reduced with sulphuric acid/iron (II) sulphate to chromium (III) sulphate, and dried in air at 100 °C. To achieve the finest possible grain size, the powder is then ground accordingly in water in a grinding ball mill After filtration and drying, a light green powder is obtained, with an average grain size of less than 1 urn. Example 4 Manufacture of neodymium-activated yttrium-cihromium-perovskite (Y0.65Nd0.09CrO3): 55.96 yttrium oxide (Y2O3,), 39,65 g chromium oxide (Cr2O3,), 4,39 neodymium oxide (Nd2O3) and 100 g dehydrated sodium sulphate (Na2SO4) are intimately mixed and heated to 1100 °C in a corundum crucible for 20 hours. After cooling, the reaction product is ground, the fluxing agent is washed out with water, the sodium chromate produced as a side-product is reduced with sulphuric acid/iron (II) sulphate to chromium (HI) sulphate, and dried in air at 100 °C. To achieve the finest possible grain size, the powder is ground accordingly in water in a grinding ball mill. After filtration and drying, a light green powder is obtained, with an average grain size of less than 1 µm. The luminescent substances can, according to the invention, be introduced to the valuable document in a variety of different ways. For example, the luminescent substances can be mixed into a printing ink, which additionally contains visible colour additives. Mixing of the luminescent substances into a paper pulp is also possible. Likewise, the luminescent substances can be applied on or in a plastic substrate material, which, for example, is at least partially embedded in a paper pulp. The substrate material may in this case take the form of a safety thread, a mottling thread, or a planchet The plastic or paper substrate material can, however, also be attached to any other desired object, for example, for product security. In this case, the substrate material is preferably made in the form of a label. If the substrate material is a constituent part of the object which is to be secured, as is the case, for example, with tear-off threads, any other shape is naturally also possible. In specific application instances it may be a good idea for the luminescent substance to be provided as an invisible coating on the valuable document. It may then be present over the entire surface, or in the form of specific patterns, such as stripes, lines, circles, or in the form of alphanumeric symbols. The designation "valuable document " is to be understood in the context of the invention to mean items such as bank notes, cheques, shares, stamps, identity cards, credit cards, passes, and other documents, as well as labels, seals, packaging, or other elements for product security. Fig. 6 shows an embodiment of a security element according to the invention. The security element consists in this case of a label 5. which is composed of a paper or plastic layer 6, a transparent covering layer 7, and an adhesive layer 8. This label 5 is attached to the desired substrate 10 by means of the adhesive layer 8. This substrate 10 may be a valuable document, identity card, pass, certificate, or similar item, or odier document to be safeguarded, such as CDs, packaging, etc. The luminescent substance 9 in this embodiment is contained in the volume of the layer 6. If this layer 6 is a paper layer, then the concentration of luminescent substance is between 0.05 and 1 % by weight. The core of luminescent substrate in the substrate (paper) is preferably in the range of 0.01 to 10% by weight As an alternative, the luminescent substance may also be contained in a printing ink, not shown, which is printed on one of the layers of the label, preferably on the surface of the layer 6. The concentration of luminescent substance in the printing ink varies in this case in the range between 10 and 30 % by weight. The core of luminescent substance in the printing ink is preferably in the range of 0.5 to 40% by weight. Instead of the luminescent substance being present in or on a substrate material, which is then attached as a security element to an object, it is also possible according to the invention for the luminescent substance to be provided directly in the valuable document to be safeguarded, or onto its surface, in the form of coating. WE CLAIM : 1. Security document, with at least one authentication mark in the form of a luminescent substance, comprising a substrate material supporting said luminescent substance, wherein the luminescent substance is based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible region of the spectrum, is excitable in substantial parts of the visible region of the spectrum and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 µm, wherein the rare earth metal emits in the wavelength range between 0.8 and 1.1 µm, and the host lattice has a garnet of perovskite structure. 2. Security document as claimed in claim 1, wherein the rare earth metal is ytterbium, praseodymium, or neodymium. 3. Security document as claimed in claim 1 or 2, wherein the host lattice contains chromium as the absorptive component. 4. Security document as claimed in any of claims 1 to 3, wherein the garnet structure can be described by the general formula A3Cr5-xAlxO12 where AD stands for an element from the group of scandium, yttrium, the lanthanides, the actinides, and the index x fulfills the condition 0 5. Security document as claimed in claim 4, wherein the index x fulfills the condition 0.3 6. Security document as claimed in claim 4 or 5, wherein the luminescent substance can be described by the formula Y3-zDzCr5-xAlxO12 where D stands for an element from the group of neodymium, praseodymium, or ytterbium, and the index z fulfills the condition 0 7. Security document as claimed in any of claims 1 to 3, wherein the perovskite structure can be described by the general formula ACrO3 where A stands for an element from the group of yttrium, scandium, or the lanthanides. 8. Security document as claimed in claim 7, wherein the luminescent substance can be described according to the formula Y1-ZDzCrO3 where D stands for an element from the group of neodymium, praseodymium, or ytterbium, and the index z fulfills the condition 0 9. Security document as claimed in any of claims 1 to 8, wherein the luminescent substance is mixed into a printing ink, which additionally contains visible colour additives. 10. Security document as claimed in any of claims 1 to 8, wherein the luminescent substance is mixed into the paper pulp. 11. Security document as claimed in any of claims 1 to 8, wherein the luminescent substance is provided on or in said substrate material, which is at least partially embedded in the paper pulp. 12. Security document as claimed in claim 11, wherein the substrate material consists of plastic. 13. Security document as claimed in claim 11 or 12, wherein the substrate material takes the form of a security thread or mottling fibre. 14. Security document as claimed in any of claims 1 to 8, wherein the luminescent substance is provided as an invisible and at least partial coating on the substrate material. 15. Security document as claimed in claim 14, wherein the coating takes the form of a stripe. 16. Security document as claimed in claim 1, wherein the luminescent substance is provided in the volume of the substrate material. 17. Security document as claimed in claim 16, wherein the luminescent substance is present in the substrate material in a concentration between 0.01 and 10% by weight, and preferably between 0.1 and 5% by weight. 18. Security document as claimed in claim 1 or 16, wherein the luminescent substance is present in a layer applied to the substrate material. 19. Security document as claimed in claim 18, wherein the luminescent substance is present in a printing ink in a concentration between 0.5 and 40% by weight, and preferably between 20 and 30% by weight. 20. Security document as claimed in any of claims 16 to 19, wherein the substrate material consists of plastic. 21. Security document as claimed in any of claims 16 to 19, wherein the substrate material consists of paper. 22. Security document as claimed in any of claims 16 to 21, wherein the substrate material takes the form of a security thread, mottling fibre, planchet, or label. 23. Security document as claimed in claim 1, which comprises a paper or plastic carrying the luminescent authenticity feature, a transparent covering layer and an adhesive layer so that it can be affixed as a label to any desired substrate by means of said adhesive layer. 24. Security document, substantially as herein described, particularly with reference to the examples and the accompanying drawings. 25. Security element, which features at least one substrate material supporting and one luminescent substance based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible spectral region, is excitable in substantial parts of the visible spectral region, and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 urn, whereby the rare earth metal emits in the wavelength range between 0.8 and 1.1 urn, and the host lattice has a garnet of perovskite structure. 26. Security element as claimed in claim 25, wherein the luminescent substance is provided in the volume of the substrate material. 27. Security document as claimed in claim 26, wherein the luminescent substance is present in the substrate material in a concentration between 0.01 and 10% by weight, and preferably between 0.1 and 5% by weight. 28. Security element as claimed in claim 25, wherein the luminescent substance is present in a layer applied to the substrate material. 29. Security element as claimed in claim 28, wherein the luminescent substance is present in a printing ink in a concentration between 0.5 and 40% by weight, and preferably between 20 and 30% by weight. 30. Security element as claimed in any of claims 25 to 29, wherein the substrate material consists of plastic. 31. Security element as claimed in any of claims 25 to 29, wherein the substrate material consists of paper. 32. Security element as claimed in any of claims 25 to 31, wherein the substrate material takes the form of a security thread, mottling fibre, planchet, or label. 33. Security element, substantially as herein described, particularly with reference to the examples and the accompanying drawings. Security document, with at least one authentication mark in the form of a luminescent substance, comprising a substrate material supporting said luminescent substance, wherein the luminescent substance is based on a host lattice doped with at least one rare earth metal, which largely absorbs light in the entire visible region of the spectrum, is excitable in substantial parts of the visible region of the spectrum and is at least partially transparent at least in the wavelength range between 0.8 and 1.1 µm, wherein the rare earth metal emits in the wavelength range between 0.8 and 1.1 µm, and the host lattice has a garnet of perovskite structure.

Documents:

IN-PCT-1999-44-KOL-CORRESPONDENCE.pdf

IN-PCT-1999-44-KOL-FORM 27-1.1.pdf

IN-PCT-1999-44-KOL-FORM 27.pdf

IN-PCT-1999-44-KOL-FORM-27.pdf

in-pct-1999-44-kol-granted-abstract.pdf

in-pct-1999-44-kol-granted-assignment.pdf

in-pct-1999-44-kol-granted-claims.pdf

in-pct-1999-44-kol-granted-correspondence.pdf

in-pct-1999-44-kol-granted-description (complete).pdf

in-pct-1999-44-kol-granted-drawings.pdf

in-pct-1999-44-kol-granted-examination report.pdf

in-pct-1999-44-kol-granted-form 1.pdf

in-pct-1999-44-kol-granted-form 13.pdf

in-pct-1999-44-kol-granted-form 18.pdf

in-pct-1999-44-kol-granted-form 3.pdf

in-pct-1999-44-kol-granted-form 5.pdf

in-pct-1999-44-kol-granted-gpa.pdf

in-pct-1999-44-kol-granted-pa.pdf

in-pct-1999-44-kol-granted-reply to examination report.pdf

in-pct-1999-44-kol-granted-specification.pdf

in-pct-1999-44-kol-granted-translated copy of priority document.pdf