HK1134710B - Authenticity mark in the form of a luminescent substance - Google Patents

Description

Authenticity mark in the form of a luminescent substance

The invention relates to a printed value document (document of value) having at least one authenticity feature in the form of a luminescent substance based on a host lattice (host lattice) doped with one or more ions.

In the context of the present invention, the term "value document" refers to banknotes, checks, stocks, tokens, Identity (ID) documents, credit cards, passports and other documents as well as labels, seals, packaging or other elements for product protection.

It has long been known to protect value documents against forgery by means of luminescent substances. The use of transition metals and rare earth metals as luminescent ions has been discussed. Such ions have the following advantages: they exhibit one or more characteristic narrow-band luminescence after appropriate excitation that facilitates reliable detection and demarcation from other spectra. Combinations of transition metals and/or rare earth metals have also been discussed. Such a substance has the following advantages: in addition to the above-mentioned luminescence, so-called energy transfer processes are also observed, which can lead to more complex spectra. In such an energy transfer process, an ion can transfer its energy to another ion, and the spectrum can then be made up of a plurality of narrow-band lines that are characteristic of the two ions.

But the number of ions having characteristic properties suitable for protecting the value document is limited. Furthermore, ions of transition metals and/or rare earth metals emit light at one or more characteristic wavelengths that depend on the nature of the ions and host lattice and are predictable. The energy transfer process also causes these features of the relevant ions to emit light.

DE 19804021a1 describes a document of value having at least one authenticity feature in the form of a luminescent substance which is based on a doped host lattice.

EP 1370424B1 describes printed documents of value having at least one authenticity feature in the form of a luminescent substance which is based on a substance doped with (3d)²A host lattice of electronically arranged ions.

Starting from this prior art, the object of the present invention is to increase the number and complexity of substances suitable as authenticity features for documents of value and in particular to provide documents of value with authenticity features in the form of luminescent substances which differ from documents of value with substances known hitherto by characteristic novel luminescence spectra and other spectral properties.

A solution to this problem can be found in the independent claims. Developments are the subject matter of the dependent claims.

The present invention is based on the following findings: certain types of ions doped in a suitable host lattice undergo exchange interactions with the same type of ions or other ions of the host lattice. The exchange interaction results in a synergistic effect. The synergistic effect is based on the nature of the exchange-coupled system (i.e. dual or multi-nuclear ion clusters).

The exchange interaction results from an electrostatic force to which unpaired electrons of adjacent magnetic ions are exposed. Magnetic ions refer to ions having unpaired electrons. The exchange interaction results in a measurable splitting of the electronic state.

Generally, at dⁿMetal (transition metal) fⁿExchange interactions may be found in metals (rare earth metals) or combinations thereof. However, the strength of the exchange interaction is very different. At dⁿIn metal clusters, the exchange interactions are strongest and the energy splitting of the cluster states (cluster states) can be up to several hundred wave numbers. For fⁿMetal clusters, exchange interactions are much weaker and the cluster state is usually split by less than 1 wavenumber.

Particularly suitable is dⁿMetal cluster or dⁿ-fⁿExchange-coupled systems of metal clusters. In such systems, the exchange interactions may be so large that they result in a fully detectable synergistic effect. The advantage of this species is that these synergistic effects are significantly different from the nature of the ions that do not undergo this exchange interaction.

In this context, two synergistic effects are particularly suitable, which are synergistic effects which manifest themselves in the luminescence behavior. This does not preclude the use of other synergistic optical and/or magnetic effects of the exchange-coupled cluster.

In a first advantageous embodiment of the invention, a suitable host lattice is ion-doped in such a way that exchange-coupled ion clusters of these doped ions are formed, whose emission spectrum can only be understood if the exchange-coupled clusters are regarded as emitting entities. The exchange-coupled cluster has an emission spectrum that is significantly different from the emission spectrum of a single ion of the dopant ions. The ions of the transition metal are preferred, which have, as the lowest luminescence transition, a spin-forbidden transition, which at the same time corresponds to an intra-configuration transition. In (3d)ⁿIn the Tanabe-Sugano diagram of ions, a suitable electronic arrangement can be found (3d)²、(3d)³And (3d)⁶. Preferably of the ion Ti²⁺、V²⁺、V³⁺、Cr³⁺、Cr⁴⁺、Mn⁴⁺、Mn⁵⁺And Ni²⁺. Also considered is (4d)ⁿAnd (5d)ⁿElectron-distributed isoelectron ions. The host lattice is a suitable pure or mixed compound having at least one representation from the group of group I metals, group II metals, transition metals and/or rare earths of the periodic table and at least one representation from the non-metal group consisting of group III to group VII of the periodic table. Host lattices which lead to strong exchange interactions in the clusters are particularly preferred.

In a second advantageous embodiment of the invention, a suitable host lattice is doped with ions, so that exchange-coupled clusters are formed by the doped ions and the magnetic ions of the host lattice. As mentioned above, the magnetic ions should have unpaired electrons. The luminescence spectrum of such a substance can be understood only when the exchange-coupled cluster is regarded as a luminescent entity. The cluster spectrum is completely different compared to the emission spectrum of the magnetic ions of the dopant ions or host lattice. The host lattice is a suitable pure or mixed compound having at least one representation of the rare earths (Ce to Yb) and at least one representation of the non-metal group consisting of the III-VII main groups of the periodic table. Furthermore, the same and at least one additional representation from the group of main group I metals, main group II metals and/or transition metals is suitable. Preferred host lattices contain the rare earth metal ion Ce³⁺、Pr³⁺、Sm³⁺、Eu³⁺、Gd³⁺And Tb³⁺. Particularly preferred are those that result in strong exchange interactions in clusters with dopant ions. For doping, ions of transition metals are preferred which have, as the lowest luminescence transition, a spin-forbidden transition which at the same time corresponds to an intra-configuration transition. In (3d)ⁿSuitable electronic arrangements can be found in the Tanabe-Sugano diagram for ions (3d)²、(3d)³And (3d)⁶. Particularly preferred is ionic Ti²⁺、V²⁺、V³⁺、Cr³⁺、Cr⁴⁺、Mn⁴⁺、Mn⁵⁺And Ni²⁺。(4d)ⁿAnd (5d)ⁿElectronically arranged isoionic ions are also suitable.

Embodiments and advantages of the invention are further explained below with reference to the drawings, the description of the drawings and the examples.

FIG. 1 shows a Cr-based alloy³⁺The energy level diagram and the luminescence transition of the conventional luminescent substance of the doped host lattice compared to the substance according to the first embodiment.

FIG. 2 shows a Cr-based alloy³⁺The luminescence spectrum of the substance according to the first embodiment compared to the conventional luminescent substance of the doped host lattice.

FIG. 3 shows a Cr-based alloy³⁺The energy level diagram and the luminescence transition of the substance of the second embodiment compared to the conventional luminescent substance of the doped europium oxide host lattice.

FIG. 4 shows a Cr-based alloy³⁺The luminescence spectra of the substances according to the second embodiment compared with the luminescence of the two conventional luminescent substances of the doped europium oxide host lattice.

Fig. 5 shows a cross section of a security element according to the present invention.

To illustrate the advantages of the invention of the first advantageous embodiment, Cr is used³⁺Doped oxide host materials are examples of such species.The depictions in fig. 1 and 2 serve to illustrate this. Cr (chromium) component³⁺Has (3d)³The electrons are arranged and the ground state is signed with a symmetrical energy state term (term) in octahedral oxidation coordination⁴A₂And (4) showing. In such host lattices, the first excited state is typically²And E state. After higher energy excitation, the alloy has low Cr³⁺The concentration of the material will usually emit light in the red spectral range at a temperature which is not too high. The luminescence transition observed here is a spin-forbidden transition because the total spin S changes by one unit (Δ S ═ 1). This results in very narrow-band emission with a long lifetime (typically in the range of 10 ms).

When increasing the chromium concentration in the same host material, a new, very narrow-band emission line with a much shorter lifetime (typically 10-100 times shorter) is observed. The luminescence is from exchange-coupled Cr³⁺-Cr³⁺And (4) carrying out pairing. The intensity of this extra line depends on Cr in the material³⁺Concentration and strength of exchange interaction, which in turn depends on the choice of host lattice. The energy position of the spectral line can be shifted by several hundred wavenumbers (see fig. 2). The reason for this is that the exchange interaction results in the splitting of the ground and first excited states into multiple states, which are best described by their total spin S, as schematically shown in fig. 1. This transition is a spin-tolerant transition where Δ S is 0. The strength of such spin-allowed transitions is typically 100 times that of spin-forbidden transitions, and shortened lifetimes are also observed for spin-allowed transitions. Other possible luminescence transitions in the cluster are also spin-forbidden and not observed in the spectrum because their intensity is very weak with respect to the spin-allowed transitions. The main advantage of these phosphors over other known phosphors is that the emission lifetime is greatly shortened with constant similarity in the spectral position and the shape of the emission band. Another advantage resides in the possibility of shifting the spectral position of the light emission band.

To illustrate the advantages of the invention of the second advantageous embodiment, Cr is used³⁺Doped europium oxide host materials are an example of such species. The depictions in fig. 3 and 4 serve as a pairThis will explain the operation. Cr (chromium) component³⁺Has (3d)³Electron alignment and ground state signed by a symmetrical energy term in octahedral oxidation coordination⁴A₂And (4) showing. In such host lattices, the first excited state is typically²And E state. Such materials typically emit light in the red spectral range upon higher energy excitation. Two narrow-band emission lines with weak photon sidebands are observed. The europium oxide host lattice shows typical Eu after higher energy excitation³⁺Light emission spectrum. The transition corresponds to Eu³⁺So-called f-transitions, signed by an energy state term^2S+1L_JExpressed, S represents the total spin, L represents the total orbital angular momentum and J represents the total angular momentum of the states. Observed in the yellow to red spectral range⁵D₀→⁷F_JA narrow-band light emitting transition.

If europium oxide host lattice is doped with Cr³⁺Ions in Cr³⁺After excitation of the ions, a new characteristic luminescence will be observed, only considering exchange-coupled Eu³⁺-Cr³⁺The new feature luminescence can only be understood when clustered. The new luminescence transition corresponds to Eu³⁺-Cr³⁺From within a cluster⁷F₀ ²E) States of to (⁷F_J ⁴A₂) A transition of the ground state energy level. In Eu³⁺-Cr³⁺In a cluster, transitions are indicated by the names of two energy state terms, e.g. the ground state of the cluster by⁷F₀ ⁴A₂) And (4) showing. The main advantage of these luminescent substances compared to other known luminescent substances is that completely new luminescence spectra occur at a constant narrow band of luminescence transitions.

By varying and combining the substances mentioned above, a multiplicity of possibilities is provided for influencing the luminescence spectrum of the luminescent substance according to the invention and thus for creating a multiplicity of security features. The synergistic effect that occurs shows a significant temperature dependence of the luminescence. This is a further advantage which allows these effects to be switched on and off with changes in the temperature under which luminescence is measured, by appropriate choice of the substance. I.e. automated tests can be performed at room temperature or selective tests can be performed at well-defined temperatures.

In addition to evaluating the luminescence spectrum, the lifetime of the luminescence can likewise be used for differentiation. When evaluating, in addition to the energy of the luminescence lines, their number and/or shape and/or their intensity may also be taken into account, with these representing any coding.

Likewise, additional luminescence centers can be introduced in the host lattice by doping with additional ions, for example transition metal ions or rare earth metal ions, and thus a combined luminescence of the two systems or an energy transfer between the systems is achieved.

When the document of value is not marked with one luminescent substance but with a plurality of luminescent substances according to the invention, the number of distinguishable combinations can be further increased.

Here, the marking can be implemented at different locations or at the same location of the value document. When the marking is applied or introduced at different locations of the value document, a spatial coding, for example a bar code in the simplest case, can be generated.

Furthermore, the forgery-proofness of the value document can be increased when, for example, a specifically selected luminescent substance in the value document is linked to further information of said value document, so that a test can be carried out by means of a suitable algorithm. Such information may be related to the value document, for example a serial number, a spatial position of certain parts of the value document, etc.

It is clear that the document of value can further have, in addition to the luminescent substance according to the invention, additional authenticity features based on, for example, classical luminescence and/or magnetism.

The luminescent substances according to the invention can be incorporated into the document of value in the most different ways according to the invention. For example, the luminescent substance may be incorporated in a printing ink. However, in the production of value documents based on paper or plastic, it is also possible to incorporate the luminescent substance into a pulp or plastic body. Likewise, the luminescent substance can be provided on or in a plastic carrier material, which can, for example, in turn be at least partially processed into pulp. The carrier material, which is based on a suitable polymer (for example PMMA) and in which the luminescent substance according to the invention is embedded, can be in the form of a security thread (security thread), a mottling fiber (mottling fiber) or a wafer (planche). Likewise, for product protection, the luminescent substance can be introduced, for example, directly into the material of the object to be protected, for example, directly into the housing and the plastic bottle.

But it is also possible to attach the plastic carrier material and/or the paper carrier material to any other object, for example for product protection. In this case, the carrier material preferably has the form of a label. When the carrier material forms part of a product to be protected, it is clear that any other design is feasible, as is the case for example with tear lines. In the case of certain applications, it can be advantageous to provide the luminescent substance as an invisible mixture as a coating on the document of value. The luminescent substance may be completely covered or in the form of a pattern, for example in the form of a strip, a line, a circle or an alphanumeric character. To ensure invisibility of the luminescent substances, according to the invention, either colorless luminescent substances in printing inks or coating lacquers (coating lacquers) have to be used, or the concentration of colored luminescent substances is so low that only the transparency of the coating is provided. Alternatively or in addition, the carrier material or the printing ink containing the luminescent substance can be dyed in a suitable manner, so that the luminescent substance is not perceptible owing to the color of the carrier material or the printing ink.

In general, the luminophores according to the invention are processed in the form of pigments. For better processing or for increasing their stability, the pigments can be present in particular as individually encapsulated pigment particles or covered with inorganic materials or organic coatings. For this purpose, for example, the individual pigment particles of the luminescent substance are encapsulated with a silicate shell and can therefore be dispersed more easily in the medium. Likewise, the different pigment particles of the combination may be jointly encapsulated, for example, in a fiber, a thread, a silicate shell. Thus, for example, it is no longer possible to change the "coding" of the combination. By "encapsulated" is meant completely surrounding the pigment particles, and by "coated" is meant partially surrounding or coating the pigment particles.

In the following, some examples of the synthesis of oxidic substances according to the invention are listed:

example 1

Manufacture of chromium activated yttrium garnet (Cr-Cr: Y)₃Al₅O₁₂)

Weighing 42.11g of alumina (Al)₂O₃) 1.02g of chromium oxide (Cr)₂O₃) 56.87g of yttrium oxide (Y)₂O₃) And mixing them with 100g of anhydrous sodium sulfate (Na)₂SO₄) Are mixed together uniformly. The mixture was filled into a corundum crucible and heated at a temperature of 1150 ℃ for 12 hours. After cooling, the resulting reaction product is ground to the desired particle size and the remaining portion of the flux (flux) is removed in a water bath. The remaining part of the chromium oxide used or by-products resulting therefrom, for example sodium chromate, is reduced (reduce) with sulfuric acid/ferrous sulfate to chromium (III) and separated. The product obtained is filtered off and dried at 100 ℃.

Example 2

Manufacture of chromium activated yttrium perovskite (Cr-Cr: YAlO)₃)

30.32g of alumina (Al) was weighed₂O₃) 1.02g of chromium oxide (Cr)₂O₃) 68.66g of yttria (Y)₂O₃) And mixing them with 100g of anhydrous sodium sulfate (Na)₂SO₄) Are mixed together uniformly. The mixture was filled into a corundum crucible and heated at a temperature of 1150 ℃ for 18 hours. After cooling, the resulting reaction product is ground to the desired particle size and the remaining portion of the flux is removed in a water bath. The remaining part of the chromium oxide used or by-products resulting therefrom, for example sodium chromate, is reduced to chromium (III) with sulfuric acid/ferrous sulfate and separated. The product obtained is filtered off and dried at 100 ℃

Fig. 5 shows an embodiment of a cryptographic element according to the invention. In this case, the security element is made of a label 2, the label 2 being constituted by a paper and/or plastic layer 3, a transparent cover layer 4, and an adhesive layer 5. The label 2 is attached to any desired substrate 1 by an adhesive layer 5. The substrate 1 may be a value document, an identity document, a passport, an escrow or the like, as well as other objects to be protected, such as CDs, packaging or the like. In this embodiment, the luminescent substance 6 is contained in the volume of the layer 3.

Alternatively, the luminescent substance can also be contained in a not shown printing ink which is printed onto one of the label layers, preferably onto the surface of layer 3.

Instead of providing the luminescent substance on or in a carrier material which is subsequently attached as a security element to an object, it is also possible according to the invention to apply the luminescent substance in the form of a coating directly in the document of value to be protected or directly on its surface.

Claims (23)

1. Authenticity feature for a document of value, in the form of a luminescent substance based on a doped host lattice, characterized in that doped ions form exchange-coupled clusters with each other, which provide a synergistic effect, and/or that the doped ions form exchange-coupled clusters with the ions of the host lattice, which provide a synergistic effect, the luminescence spectrum of which is only understood when the exchange-coupled clusters are regarded as a luminescence entity.

2. The authenticity mark of claim 1 wherein said synergistic effect results from an exchange interaction between unpaired electrons of adjacent ions.

3. The authenticity mark according to claim 1 or 2, wherein said dopant ions have an electronic arrangement (3d)²、(3d)³Or (3d)⁶Or with the respective electronic arrangement of the (4d) or (5d) transition metals.

4. Authenticity mark according to any of claims 1-3, wherein said host lattice is a pure or mixed compound with at least one representation from the group of group 1 main group metals, 1I main group metals, transition metals and/or rare earths of the periodic Table of the elements and at least one representation from group 1II to VII of the periodic Table of the elements.

5. The authenticity mark according to any of claims 1-3, wherein said host lattice is a pure or mixed compound having at least one representation of rare earths (cerium-ytterbium) and at least one representation of a non-metal from main groups 1II to VII of the periodic Table of the elements.

6. Authenticity mark according to claim 5, wherein said compound additionally contains a representation from the group of group 1 main group metals, 1I main group metals and/or transition metals.

7. Authenticity mark according to any one of claims 1 to 6, wherein said host lattice is additionally co-doped with at least one representation from the group of rare earth metals.

8. The authenticity mark according to any of claims 1 to 7, wherein said luminescent substance is present as pigment particles.

9. Value document having an authenticity feature according to any of claims 1 to 8, wherein the value document consists of paper and/or plastic.

10. The value document according to claim 9, wherein the authenticity mark is incorporated into the volume of the value document and/or is coated on the value document.

11. A document of value according to claim 9 or 10, wherein the luminescent substance is applied to the document of value as an invisible at least partial coating.

12. A value document according to any one of claims 9 to 11, wherein the luminescent substance is incorporated into a printing ink.

13. A document of value according to any of claims 9 to 12, wherein the luminescent substance is combined with at least one different authenticity feature.

14. The document of value of any of claims 9 to 13, wherein the at least two luminescent substances form a spectral coding in at least one spatial dimension.

15. Cryptographic element having a carrier material and at least one authenticity feature according to any of claims 1 to 8, wherein the authenticity feature is embedded in and/or coated on the carrier material.

16. The cryptographic element of claim 15, wherein the cryptographic element has the form of a strip or a band.

17. A security element as claimed in claim 15 or claim 16 in which the carrier material is formed as a security thread, disc or speckle fibre.

18. The cryptographic element of any of claims 15-17, wherein the cryptographic element is formed as a label.

19. Method for producing a document of value according to one of claims 9 to 14 or a cryptographic element according to one of claims 15 to 18, wherein the luminescent substance is added to a printing ink.

20. Method for manufacturing a document of value according to any of claims 9 to 14 or a cryptographic element according to any of claims 15 to 18, wherein the luminescent substance is applied by a coating process.

21. Method for producing a document of value according to one of claims 9 to 14 or a security element according to one of claims 15 to 18, wherein the luminescent substance is processed into the volume of the document of value.

22. Method for producing a document of value according to one of claims 9 to 14 or a security element according to one of claims 15 to 18, wherein the luminescent substance is provided to the document of value by means of correspondingly produced speckle fibres.

23. Method for producing a document of value according to one of claims 9 to 14 or a security element according to one of claims 15 to 18, wherein the luminescent substance is provided to the document of value by means of a correspondingly produced security thread.