Method for evaluating volatile non-resistant Anti-stokes luminescent substances on value documents, device for verifying such security elements and such security elements

Abstract

The invention relates to a security element (2) with a pattern (110) made of pattern regions (120) as a security feature (100). The pattern regions (120) comprise at least one first pattern region (121, 121-x) and a second pattern region (122, 122-x), and the first pattern region (121, 121-x) and the second pattern region (122, 122-x) have an anti-Stokes luminescent substance (200) in a non-manipulated state of the security element (2), said luminescent substance exhibiting a luminescence in an anti-Stokes wavelength range when excited with a light signal (407) with a wavelength in an excitation wavelength range. The first pattern region (121, 121-x) and the second pattern region (122, 122-x) differ in that the content of anti-Stokes luminescent material (200) which can be removed from the security element (2) by manipulation is greater in the second pattern region (122, 122-x) than in the first pattern region (121, 121-x). The invention additionally relates to a verification method and a device for verifying such a security element (2), wherein an evaluation of the anti-Stokes luminescence is carried out via a respective communication attachment.

Description

[0001] The invention relates to a method for verifying safety elements comprising anti-Stokes luminescent materials, as well as a device for verifying such safety elements and the safety elements themselves.

[0002] Anti-Stokes phosphors for use in safety documents are known from EP 1 241 242 A2. These anti-Stokes phosphors belong to the group of photoluminescent materials, which can be excited by electromagnetic radiation to emit electromagnetic luminescence. Anti-Stokes phosphors absorb electromagnetic radiation of a wavelength known as the excitation wavelength and emit at least some of the luminescence radiation at an anti-Stokes wavelength that is shorter than the excitation wavelength.

[0003] EP 1 241 242 A2 states that the decay times and / or decay times of the anti-Stokes luminescence can be evaluated for automatic detection of the anti-Stokes phosphor. These decay times and / or decay times are characteristic of the various anti-Stokes phosphors. Furthermore, it is known that the decay times of anti-Stokes phosphors are relatively long compared to many other luminescent materials and can reach up to several hundred microseconds.

[0004] WO 2006 / 099642 A1 discloses a security feature for a security document, wherein the security document comprises a base body made of a base material, comprising a first luminescent substance. To increase counterfeit protection, it is proposed that a second luminescent substance be provided, that energy transfer be provided between the first and second luminescent substances, wherein the frequency range of the excitation of one of the luminescent substances corresponds to the frequency range of the emission of the other luminescent substance, and that the first luminescent substance be thermally unstable at the ignition temperature of the base material and / or at a temperature of 185°C.

[0005] WO 2010 / 006583 A2 relates to a process for manufacturing a security and / or valuable product, in particular a security and / or valuable document, comprising the following process steps: a) a substrate is coated with a marking layer containing a luminescent substance, b) a plurality of sub-areas of the marking layer are modified, forming a defined pattern unique to the security and / or valuable product, with the proviso that the luminescence emission of the luminescent substance is increased or decreased in the sub-areas, c) a character string is assigned to the pattern produced in step b) in a preferably unique manner, d) the character string assigned in step c) is applied to the security and / or valuable product as an identification string in a readable manner and / or is integrated therein in a readable manner.Furthermore, a security and / or value product obtainable by means of the described procedure, as well as a procedure for verifying such a security and / or value product, are described.

[0006] WO 2008 / 132223 A2 describes the use of a phosphor with the formula (Y 1-xy Yb x Er y )2O3 with x = 0.20 and y = 0.075 as a security feature with anti-Stokes luminescence. When excited with an IR laser, these phosphors exhibit two peaks in the range of 540 nm and 670 nm, the intensity ratio of which varies considerably and depends not only on the proportion of Yb and Er, but also, for example, on the particle size. If the phosphor is in the form of nanoparticles, preferably with a size of 0.1–0.5 µm, not only is the peak at 670 nm favored, but there is also the advantage that the nanoparticles are invisible under normal light and do not impair print quality. A security printing ink containing such a phosphor is also described, as well as a method and a device for checking a document and a document containing such a phosphor as a security feature.

[0007] US Patent 2013 / 234043 A1 discloses a method for illuminating an object. The method comprises applying an adhesive to the object, incorporating a marking agent into the adhesive, illuminating the object with an excitation signal, detecting the luminescence emitted by the marking agent in response to the illumination by the excitation signal, and determining the authenticity of the object based on the detected emitted luminescence. The object can be any authentication item, such as a postage stamp. Additionally, a method for personalizing an object is disclosed. This method can include the following steps: preparing a substrate, applying a security feature to the substrate, printing non-customer-specific information onto the substrate, receiving image information, and printing the image information onto the substrate.

[0008] WO 2014 / 140431 A1 provides a method for applying a security mark to an object and a "hyper-spectral" imaging device for reading the information embedded in the security mark to verify the object's authenticity. The described method relates generally to the field of security marking and anti-counterfeiting. In particular, it concerns optical product authentication methods based on photoactive nanoparticles that emit light in the visible and near-infrared wavelength range when excited by ultraviolet or near-infrared light.

[0009] Security documents are known from the prior art in which anti-Stokes phosphors are integrated into security features, and anti-Stokes luminescence and, if applicable, its specific characteristics are used as a security feature. In the simplest verification, this merely checks whether anti-Stokes luminescence can be detected.

[0010] In a further developed embodiment, for example, the decay time and / or decay time are evaluated and, based on this evaluation, it is checked whether the tested security document contains the correct anti-Stokes luminescent substances for a genuine security document.

[0011] As technological advancements enable counterfeiters of security documents to imitate and / or replicate increasingly complex security features, such as anti-Stokes luminescent materials, security document manufacturers strive to use ever more sophisticated security features that are nevertheless reliably verifiable. Furthermore, it is desirable to be able to detect any tampering with security elements.

[0012] For postage stamps that are affixed to documents or objects with an adhesive and are intended for single use, a problem arises, for example, that they can be detached and reused. Various measures can be taken to prevent this. Postage stamps are canceled, for instance, by printing or stamping on information. However, during processing in sorting and / or canceling machines, it can happen that individual postage stamps are not canceled. Furthermore, it is sometimes possible to remove the printed information. Thus, detached postage stamps that have been manipulated by detaching them from the originally transported mail item and / or by removing the printed information used for cancellation are reused.

[0013] Other security elements, such as labels, visa stamps, etc., which are applied to documents or objects for security purposes, can also be manipulated and used without authorization in a similar way.

[0014] The invention is based on the objective of being able to detect and / or prevent such manipulations. Basic idea of ​​the invention

[0015] The invention is based on the idea of ​​creating a security feature comprising an anti-Stokes luminescent material. Part of the anti-Stokes luminescent material is applied to or integrated into the security feature in such a way that this portion is removed from the security feature during any tampering process. Another part of the anti-Stokes luminescent material is applied to or integrated into the security feature in such a way that it is not removed during any tampering process. The security feature is provided to include a pattern formed from patterned areas as a security feature, wherein the patterned areas comprise at least two types of patterned areas, in each of which an anti-Stokes luminescent material is applied to and / or incorporated, preferably homogeneously.The sample areas differ in that the relative proportion of anti-Stokes luminescent material that can be removed from the respective sample area upon manipulation is greater for one type of sample area than for the corresponding sample areas of the other type. Hereinafter, sample areas of one type with a greater relative proportion of removable anti-Stokes luminescent material than those of the other type are referred to, without restriction of generality, as second sample areas, and sample areas with a smaller relative proportion of removable anti-Stokes luminescent material are referred to as first sample areas.The relative proportion of anti-Stokes luminescence removable during tampering is defined as the ratio of the anti-Stokes luminescence removable during tampering to the total amount of anti-Stokes luminescence in the corresponding pattern area before tampering, i.e., in a genuine and intact security feature. The proportion of anti-Stokes luminescence removable during tampering can be zero for one type of pattern area. The security feature thus comprises a pattern that, when evaluating the anti-Stokes luminescence in the tampered state, the untampered state, or both states, can be detected as consisting of different pattern areas.

[0016] To reliably verify such a security element, particularly in situations where the time available for verification is limited, one aspect of the invention considers and evaluates the excitation of anti-Stokes luminescence in the sample areas, the detection of the anti-Stokes luminescence, and its conversion into an output signal whose amplitude is a measure of the detected anti-Stokes luminescence light intensity as a single communication process. This reduces the time required for evaluation and increases the accuracy of the verification for the presence of a specific anti-Stokes luminescent substance.This creates the possibility, firstly, of verifying that, during a scanning or scanning excitation and detection of anti-Stokes luminescence across the pattern, the detected anti-Stokes luminescence originates from a specific, expected anti-Stokes luminescent substance used in the patterns of genuine security features. This allows genuine security features to be protected against counterfeits that, while possessing an anti-Stokes luminescence security feature, are not manufactured with the correct anti-Stokes luminescent substance.In addition, the possibility is created to identify the different pattern areas either in manipulated security elements, in non-manipulated security elements or in both manipulated and non-manipulated security elements, and to detect manipulation of security elements based on information about the genuine pattern of a genuine security element, which is caused by a manipulation act, for example, detaching and reusing the security element, on an originally genuine security element.

[0017] With a verification device designed to excite anti-Stokes luminescence and detect the anti-Stokes luminescent light, and to perform such an evaluation of the information, it is possible to verify these novel security elements.

[0018] To examine the verification process from a communications engineering perspective, the verification of the security feature using anti-Stokes luminescence is first conceptually divided into different stages. Firstly, the verification process involves excitation with electromagnetic radiation in a wavelength range that can lie in the infrared (IR), visible, or ultraviolet (UV) spectrum. This electromagnetic radiation then causes a physical response in the security feature being verified in the form of a luminescence response, i.e., an emission of anti-Stokes luminescence. This emission is detected by a measuring device that provides an output signal.It has proven advantageous to consider the luminescence response of the security feature, including the measuring apparatus that detects the anti-Stokes luminescence and converts it into an output signal, as a signal transmission path and to model it using a characteristic function. This characteristic function, whose shape depends essentially on the anti-Stokes luminescent material, represents a system response to standard optical excitation with electromagnetic radiation from the excitation wavelength range of the anti-Stokes luminescent material applied to or within a sample area. The characteristic function incorporates all influences of both the security feature and the measuring apparatus and signal conversion up to the generated output signal. The characteristic function is thus preferably a system response, also called a standard system response, to standardized excitation.For example, the characteristic function describes the step response during the verification of an anti-Stokes luminescent substance in a genuine security feature. This response occurs when the measurement signal, which is the luminescence light intensity of the verification device used for further evaluation, is subjected to a sudden, otherwise constant excitation with a predefined excitation radiation. In practical terms, an impulse response can be used instead of a step response. This represents the response of the measurement signal to excitation with excitation radiation whose intensity can be specified by a function describing an impulse, such as a rectangular or triangular function.

[0019] Such a characteristic function can be determined from measurements and / or numerical simulations.

[0020] It has been shown that, based on the output signal recorded by the measuring apparatus and the characteristic function, it is possible to determine whether the output signal represents the expected response of the safety feature for the excitation used, and thus to verify whether the phosphor corresponding to the characteristic function is contained in the safety feature at the location where the excitation is carried out.

[0021] This method makes it possible to vary the excitation and to perform measurements even without a fully steady and stable state. For example, information can be transmitted in the form of symbols.

[0022] In the following, a symbol will be defined as a single unit of meaning used to transmit information. A symbol has a specific shape. Specifically, a symbol here will be understood in the context of telecommunications, where a transmission unit sends symbols over a transmission channel to transmit data, and a receiving unit recognizes these symbols and reconstructs the transmitted data.

[0023] Knowing the characteristic function, it is now possible to control the excitation, for example, via an input signal in which information is stored or encoded in the form of symbols. A symbol is defined by a function of the envelope of the intensity of the electromagnetic excitation radiation in the time domain, i.e., by a function that specifies the intensity of the electromagnetic excitation radiation as a function of time. During verification, it can then be checked whether symbols can be recognized in the output signal or the signal obtained after evaluation. It will not always be necessary to determine the symbol sequence itself. Knowledge of the symbol shape is sufficient to determine whether a symbol sequence is contained in the evaluated output signal.This alone is sufficient to achieve an improved signal-to-noise ratio compared to classical measurement methods in the state of the art, thus significantly increasing the selectivity in verification as well as the verification speed and spatial resolution of the verification. Definitions

[0024] Luminescence is the physical property of a substance to emit electromagnetic radiation after being excited. The electromagnetic radiation produced during luminescence is also called luminescent radiation or luminescent light. The wavelengths of luminescent radiation can lie in the infrared, visible, and / or ultraviolet (UV) range.

[0025] If luminescence is excited by light in the infrared, visible, or ultraviolet wavelength range, it is also called photoluminescence. Generally, the wavelength of the luminescent light is longer than the wavelength of the excitation light used to excite the luminescent substance.

[0026] However, physical processes can also occur within a luminescent material that result in the luminescence light having a shorter wavelength than the excitation light used for excitation. Such luminescence is called anti-Stokes luminescence or up-conversion luminescence, or simply upconversion, because the energy of an emitted anti-Stokes luminescence photon is higher than the energy of the photons in the excitation light.

[0027] A pattern is defined as an arrangement of pattern regions, also called pattern elements, relative to one another in space. These pattern regions can have similar properties or be different from each other. For example, pattern regions can be areas that exhibit a specific property. The shapes and arrangement of areas that, for instance, exhibit a specific anti-Stokes luminescence when excited with a particular wavelength on the surface of a security feature define a pattern. A pattern revealed by an anti-Stokes luminescence test consists of pattern regions or pattern elements, which are planar areas that can be distinguished based on their anti-Stokes luminescence in the unmanipulated state, the manipulated state, or both.A pattern region comprises a contiguous area where the same anti-Stokes luminescence is observable at every location within the region. An area exhibiting the same observable / measurable anti-Stokes luminescence properties at all locations, both in the unmanipulated and manipulated states, does not constitute a pattern as described here. A pattern must therefore have at least two pattern regions or pattern elements that differ in a measurable property of the anti-Stokes luminescence described here, in one or both states—that is, in the unmanipulated state, the manipulated state, or both.

[0028] Genuine security features always exhibit at least two distinct pattern areas, each displaying anti-Stokes luminescence in its unmodified state. However, the anti-Stokes luminescence of these areas differs in at least one of the two states. Patterns can have more than the minimum of two pattern areas. The anti-Stokes luminescence of these additional areas may be the same as, or different from, that of one of the minimum two pattern areas. Furthermore, some embodiments may also include areas that do not exhibit anti-Stokes luminescence.

[0029] Anti-Stokes luminescent materials are different within the meaning of the invention described herein if the luminescence intensities of the anti-Stokes luminescent materials integrated over a predetermined anti-Stokes luminescence wavelength range exhibit different time behaviors under the same excitation.

[0030] The anti-Stokes luminescence of one sample area differs from the anti-Stokes luminescence of another sample area if the luminescence exhibits a different time response or if their luminescence intensities differ under the same excitation, i.e., differ by a definable value, for example, by more than 20%, more than 50%, more than 200%, or more than 500% (in each case relative to the intensity of the area with the lower luminescence intensity).

[0031] The fact that an anti-Stokes luminescent material is removable by tampering means that, during an action such as peeling the security element from an object (e.g., a postage stamp from a letter), it is removed from the substrate or other physical unit that forms the security element, without the substrate or other physical unit being removed or reduced in size (except perhaps for a change in the thickness of the layer in which the anti-Stokes luminescent material is applied). As a rule, the tampering will not be detectable by visual inspection by a human observer or by image recognition analysis of a picture captured in the visible wavelength range.An anti-Stokes luminescent material is removable, for example, because the preparation with which the anti-Stokes luminescent material is applied to or integrated into the security element, or the resulting layer, is soluble in a fluid used to remove the security element, or has low abrasion resistance, or exhibits low stability under heat and, for example, shows a tendency to transition into the gaseous or liquid phase when exposed to heat, i.e., to evaporate or sublimate, whereby the anti-Stokes luminescent material is removed with or escapes from the preparation or the resulting layer.An anti-Stokes luminescent material is considered non-removable, for example, if the preparation used to apply or integrate the anti-Stokes luminescent material onto the security element, or the resulting layer, exhibits high stability against environmental influences during tampering, e.g., abrasion-resistant, insoluble, and heat-resistant, at least to the extent that occurs during tampering that would otherwise not affect the security element or would not noticeably impair it. A key aspect of the invention is that in one sample area, the anti-Stokes luminescent material is introduced in such a way that it is removed due to the environmental influences occurring during tampering, while in another sample area, it is not removed due to the same environmental influences.

[0032] A characteristic function of an anti-Stokes luminescent substance specifies the functional relationship between a predefined standardized excitation of the anti-Stokes luminescent substance in a genuine security feature and a measurement signal generated during verification in a verification device. If anti-Stokes luminescence in an area of ​​a security feature is determined not only by a single anti-Stokes luminescent substance but by a combination of anti-Stokes luminescent substances, then a characteristic function can also be assigned to this combination of luminescent substances. This characteristic function specifies the functional relationship between the predefined standardized excitation of the combination of anti-Stokes luminescent substances in a genuine security feature and a measurement signal generated during verification in the verification device. Bevorzugte Ausführungsformen

[0033] The invention provides a method for verifying security elements as defined in claim 1.

[0034] One advantage over the prior art embodiments is that a much faster decision can be made regarding the existence or non-existence of an anti-Stokes luminescent substance in the currently illuminated area or the area illuminated shortly before.

[0035] A device for verifying security elements with a pattern formed from pattern areas as a security feature, wherein the pattern areas comprise an anti-Stokes luminescent material, is defined in claim 7.

[0036] Furthermore, a security element as defined in claim 8 is created with a pattern formed from pattern areas as a security feature.

[0037] One embodiment of the security feature provides that the surface concentrations of the anti-Stokes luminescent substance in the first pattern area and in the second pattern area are equal in the untampered state. This allows verification that the overall pattern formed by the first and second pattern areas, or one or more first pattern areas and one or more second pattern areas, exhibits the expected anti-Stokes luminescence at all positions in the untampered state of the security feature, thus confirming the presence of the expected anti-Stokes luminescent substance. In this case, the pattern in the untampered state is an area exhibiting uniform, homogeneous anti-Stokes luminescence.

[0038] If a security element is manipulated, for example, if a postage stamp is removed in whose second pattern area the anti-Stokes luminescent substance is applied by means of a water-soluble or steam-soluble preparation, the anti-Stokes luminescent substance will be at least partially or completely removed in the second pattern area(s) when the stamp is removed.

[0039] If, in the manipulated state, the anti-Stokes luminescent substance is completely removed from one or more of the second sample areas, the absence, i.e., the non-existence, of the anti-Stokes luminescent substance will be detected in this area or these areas during verification. This can indicate manipulation.

[0040] Patterns in which the anti-Stokes luminescent material in the second pattern area is completely removed upon manipulation preferably comprise a sequence of pattern areas of the form: first pattern area – second pattern area – first pattern area. Manipulations of such security elements can be scanned during verification regardless of orientation, i.e., in two opposite directions, without compromising detection reliability. Manipulations can thus be detected very reliably.

[0041] For security elements whose patterns consist only of the sequence first pattern area - second pattern area or the sequence second pattern area - first pattern area - second pattern area, tampering can also be detected if the extent of the area in which the correct anti-Stokes luminescence is detected is also evaluated and compared with specifications for a genuine security element.

[0042] One embodiment therefore provides that the evaluation involves creating a verification pattern based on the recognition decisions derived in temporal sequence, taking into account the movement of the illumination area relative to the security element, and deriving the verification decision based on a comparison of the verification pattern with a predetermined authenticity or counterfeit pattern.

[0043] Verification reliability is further increased, as is the "hiding" of the feature, in embodiments where the verification procedure provides that the derivation of the recognition decisions includes establishing the existence and determining a luminescence intensity attributable to the correct (i.e., expected) anti-Stokes luminescent agent, which is a measure of the amount of the expected, i.e., correct, anti-Stokes luminescent agent in the illumination area.

[0044] During evaluation, the recorded output signal is typically normalized. If the concentration of the anti-Stokes luminescent substance changes from one sample area to the next, i.e., from a first sample area to a second sample area or vice versa, this becomes apparent during evaluation because the normalization requires adjustment or would at least be advantageous. This is comparable to changing the measuring range on a measuring instrument when a parameter of the measured signal changes significantly, in order to ensure optimal data acquisition in each case.

[0045] With this embodiment, patterns can be verified very reliably even if all pattern areas exhibit the anti-Stokes luminescent substance in both the manipulated and unmanipulated states, or if not all of the removable portion of the anti-Stokes luminescent substance is removed during manipulation. However, in at least one state, the concentrations of the anti-Stokes luminescent substance differ between the various pattern areas. Without precise analysis, this is often undetectable because the anti-Stokes luminescence is observable / measurable across the entire surface of the first and second pattern areas when excited. Thus, the security feature is concealed in this case.

[0046] One embodiment of the safety element therefore provides that the anti-Stokes luminescent material of the second pattern area cannot be completely removed during manipulation.

[0047] To reliably detect the different areas of the security element that exhibit varying levels of anti-Stokes luminescence while the illumination area sweeps across the security element, it has proven advantageous to generate the time-intensity modulated light signal according to the input signal in such a way that the intensity of the light signal is modulated according to a recurring light excitation intensity pattern. The input signal thus provides the same recurring light excitation intensity pattern. Information contained within this recurring light excitation intensity pattern can be used to determine whether this information about the triggered anti-Stokes luminescence has been transferred to the output signal during verification. If so, the correct anti-Stokes luminescent material is present in the corresponding area.

[0048] A light excitation intensity pattern represents the intensity of the excitation light over time. In the context described here, a light excitation intensity pattern is assigned to a unit of information, also referred to as a symbol. The light signal modulated according to a light excitation intensity pattern, which is used for excitation, thus represents a symbol. If the light signal is iteratively modulated with the same light excitation intensity pattern, the same information is transmitted multiple times via the safety element to the evaluation unit.

[0049] In order to obtain a robust evaluation, one embodiment provides that the light signal used for excitation is modulated in time so that symbols are transmitted iteratively.

[0050] The evaluation is simplified if the iteratively transmitted symbols have the same symbol shape.

[0051] To minimize symbol interference during message transmission via light signal modulation, it is preferably provided that each symbol comprises an excitation component and a non-excitation component. In the non-excitation component, also referred to as the pause component, the light signal has no intensity or an intensity unsuitable for exciting anti-Stokes luminescence. Including the non-excitation component significantly minimizes intersymbol interference during evaluation.

[0052] Embodiments have proven advantageous in which the excitation component consists of a linear increase in intensity followed by a linear decrease in intensity. Preferably, the intensity rises from zero and then falls back to zero.

[0053] The excitation component can therefore preferably be described by a triangular signal. The light intensity initially increases linearly to a maximum value and then decreases linearly again. Preferably, the linear slopes are equal in magnitude for both the increase and the decrease, but have opposite signs. The excitation component thus represents two sides of an isosceles triangle.

[0054] Therefore, in a preferred embodiment, the excitation component consists of a linear increase in intensity and a subsequent linear decrease in intensity, wherein the slopes of the increase in intensity and the decrease in intensity are equal in magnitude.

[0055] To achieve high reliability in pattern recognition, it is advantageous to transmit multiple symbols while the illumination area scans, i.e., scans, a pattern area. To enable reliable identification of the different areas, one embodiment provides that the modulation of the light signal is synchronized with the movement speed of one of the safety elements relative to the illumination area and the extent of the illumination area along the direction of movement of the safety element. Furthermore, the modulation occurs according to several, preferably 2 to 10, more preferably 3 to 7, temporally successive symbols (light excitation intensity patterns) during the time interval in which a point of one of the safety elements moves through the excitation area or in which the excitation area scans a point of one of the safety elements.

[0056] One embodiment therefore provides that the relative movement of the illumination area and the safety element at a certain speed and the modulation of the light signal, taking into account an extension of the pattern areas parallel to the relative direction of movement, are coordinated in such a way that the anti-Stokes luminescent material is excited during the relative movement of the illumination area over the respective pattern area with a minimum number of symbols modulated onto the light signal, wherein the minimum number is greater than 2.

[0057] Preferably, the minimum number of symbols is greater than or equal to 5.

[0058] The detection of anti-Stokes luminescence is preferably performed at a frequency that is 20 times, and preferably 100 times or more, higher than the symbol modulation frequency used to modulate symbols onto the light signal. This ensures sufficient resolution of the transmitted symbol shape to guarantee reliable detection of anti-Stokes luminescent substances.

[0059] Advantageous embodiments of the safety element provide that the pattern comprises several first pattern areas similar to the one first pattern area and / or several second pattern areas similar to the one second pattern area.

[0060] In particular, patterns can be formed in which the anti-Stokes luminescence concentration fluctuates alternately between the first and second pattern regions in at least one of the states.

[0061] Preferably, the first sample area illuminated is one in which at least a large proportion of the anti-Stokes luminescent material is permanently, and in particular permanently, impervious to removal or dissolution. This allows for the verification procedure to be performed with appropriate normalization during evaluation and / or an excitation intensity of the light signal that enables optimal evaluation. If the luminescence intensity is too low, the intensity of the light signal can be increased.

[0062] For this purpose, it is advantageous if several symbols are transferred across the anti-Stokes luminescent fabric of a pattern area while it is being scanned.

[0063] If, after a normalization and excitation intensity have been selected, a transition to a different pattern area occurs, the resulting change in intensity can be reliably detected, for example, by the need for a normalization adjustment or the need to adjust the excitation intensity of the light signal. Here, too, it is advantageous if several symbols are transmitted with the illumination area while scanning a pattern area.

[0064] In one embodiment of the security element, the surface concentrations of the anti-Stokes luminescent agent are equal in the first and second non-removable sample areas. In the manipulated state, uniform luminescence is observed in both sample areas. However, in the unmanipulated state, the surface concentration of the anti-Stokes luminescent agent is higher in the second sample area(s) than in the first sample area(s).

[0065] Preferably, the area concentrations are chosen such that, in the unmanipulated state, they differ from each other by a factor of 2 or more. This ensures that the intensity of the anti-Stokes luminescence increases sharply when transitioning from the first sample area to a second sample area, unless the excitation intensity is adjusted. For example, saturation of the measuring device may occur, i.e., a (preferably linear) range may be exceeded in which the generated output signal is a measure of the detected anti-Stokes luminescence. In this case, the occurrence of saturation can be used to detect the second area. However, under normal circumstances, detection of the specific anti-Stokes luminescent substance is limited or impossible at saturation, so the intensity of the light signal is adjusted to verify its "identity."As stated above, it is checked whether, after an adjustment of the excitation intensity, one or more symbols are transmitted in the output signal as expected.

[0066] This light signal adjustment can be performed proactively, i.e., before the measuring device is expected to reach saturation. The excitation intensity can thus be adapted to an expected pattern of the safety element being verified.

[0067] Particularly preferred are embodiments in which the surface concentrations of the anti-Stokes luminescent agent in the first and second sample areas are not the same in either the unmanipulated or manipulated state, so that the different sample areas can be detected based on the anti-Stokes luminescence in both the unmanipulated and manipulated states. For example, the anti-Stokes luminescent agent in the first sample areas is exclusively applied or incorporated in a non-removable manner. The proportion of non-removable anti-Stokes luminescent agent in the second sample area, on the other hand, is significantly lower or zero. However, the removable applied or incorporated portion in the second sample area is selected, for example, such that the surface concentration of the anti-Stokes luminescent agent in the unmanipulated state is significantly higher in the second sample area than in the first sample area.In the manipulated state, this relationship is reversed.

[0068] A safety element is preferably designed such that a detection direction exists with respect to which the first and second pattern areas alternate in the pattern and the first and the last of the pattern areas along the detection direction are either a first pattern area or a second pattern area.

[0069] One embodiment provides that, in the unmodified state of the security element, no areas exist within the pattern between the pattern regions that do not contain the anti-Stokes luminescent material. Thus, the extent of the entire pattern can be automatically detected, at least in the unmodified state.

[0070] In a preferred embodiment, the safety features are designed such that the graphic pattern recognizable by an evaluation of the anti-Stokes luminescence in the anti-Stokes luminescence wavelength range is not recognizable to a human observer when excited with electromagnetic radiation in the excitation wavelength range, since, for example, in addition to the anti-Stokes luminescence, a "normal" photoluminescence also occurs in the area of ​​the pattern.

[0071] "Normal" photoluminescence occurs, for example, when the anti-Stokes luminescent substance exhibits "normal" photoluminescence in addition to the anti-Stokes luminescence.Furthermore, a luminescent substance can be applied or introduced over the pattern areas, which, when excited to the anti-Stokes luminescence in the wavelength range whose wavelength is greater than that of the anti-Stokes luminescence, exhibits "normal" photoluminescence, preferably showing a higher intensity in the humanly perceptible wavelength range or over the entire emission wavelength range, including the anti-Stokes luminescence wavelength range, so that the intensity differences of the pattern due to the luminescence of the anti-Stokes luminescent substance of the security element are not perceptible in either the unmanipulated or the manipulated state, that is, the luminescence of the anti-Stokes luminescent substance is preferably at least one or more orders of magnitude smaller than the luminescence of the other luminescent substance.

[0072] To prevent interference with the evaluation of anti-Stokes luminescence by such "normal" luminescence or other light emissions outside the anti-Stokes luminescence wavelength range, one embodiment provides for wavelength-selective filtering of the luminescence light emitted by the security feature. A verification device includes a filter for this purpose. A particularly preferred option is the use of an edge filter that attenuates the intensity of light emitted by the security feature with a wavelength greater than a maximum wavelength in the anti-Stokes wavelength range by one, preferably several, orders of magnitude, and most preferably completely.

[0073] In one embodiment, it is provided that the at least two areas of the graphic pattern, when excited with the same light signal in the excitation wavelength range for anti-Stokes luminescence, each exhibit luminescence in the visible wavelength range, which produces the same color impression on a human observer.

[0074] When the light signal intended for verification is applied to excite anti-Stokes luminescence, the graphic pattern is hidden from the observer. While the observer can recognize that a luminescence security feature is present, they cannot see that it exhibits a graphic pattern, which is detectable when the luminescence is evaluated only within the anti-Stokes luminescence wavelength range.

[0075] It is also possible to implement designs in which the extent of the illumination area along the direction of movement of the safety element is smaller than the extent of the safety element along the direction of movement.

[0076] The iterative acquisition of the anti-Stokes luminescence is preferably carried out at time intervals that are at least one order of magnitude, preferably at least two orders of magnitude, smaller than the duration of the excitation component of the light excitation intensity pattern.

[0077] The invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a schematic representation of an embodiment of a device for verifying a security element on a valuable or security document; Fig. 2 a schematic top view of a security element according to Fig. 1 Fig. 3a a graphical representation of the area concentration of an anti-Stokes luminescent substance along an x-direction of a security element in the untampered state; Fig. 3b a graphical representation of the area concentration of an anti-Stokes luminescent substance along an x-direction of a security element in the tampered state; Fig. 4a a schematic representation of a security element; Fig. 4b a schematic graphical representation of the area concentration of the anti-Stokes luminescent substance versus an extent of the pattern of a security element along a spatial direction in the untampered state; Fig. 4c a schematic graphical representation of the area concentration of the anti-Stokes luminescent substance versus an extent of the pattern of a security element along a spatial direction in the tampered state; Fig.Fig. 4: A schematic representation of the intensity of the input signal used to excite and modulate the light signal, plotted against time; Fig. 4: A simplified graphical representation of the intensity of the light signal used for excitation, plotted against time; Fig. 4: A highly simplified representation of the detected anti-Stokes luminescence light intensity for a security element in its untampered state, plotted against time; Fig. 4: A highly simplified graphical representation of the determined normalization value for the detected anti-Stokes luminescence light intensity according to... Fig. 4f plotted against time; Fig. 4 a schematic representation of an input signal, where for simplification only the maximum amplitude of the transmitted symbols is plotted; Fig. 4 a highly simplified representation of the anti-Stokes luminescence light intensity for an untampered security element when excited according to the input signal according to Fig. 4h ; and Fig. 4 a highly simplified representation of the anti-Stokes luminescence light intensity for a manipulated security element when excited according to the input signal according to Fig. 4h .

[0078] In Fig. 1 Figure 1 shows a schematic representation of an embodiment of the device 1 for verifying a security element 2 having anti-Stokes luminescence on a valuable or security document 3. The device 1 comprises an excitation device 4, a detection device 5, and an evaluation device 6.

[0079] The excitation device 4 comprises a light source 401, which is preferably designed as a laser. The excitation device 4 generates a light signal 407.

[0080] The security document 3 is arranged on a transport device 7. The transport device 7 moves the security document 3, on which the security element 2 is located, preferably along a spatial direction 91. The movement preferably takes place at a constant speed in one direction.

[0081] Alternatively or additionally to the transport device 7, the illuminated area can be moved relative to the safety element 2 by means of a deflection unit 119, for example an adjustable, controllable mirror or similar device. A control unit 17 controls the transport device 7 and the excitation device 4, as well as, optionally, such a deflection unit 119, which in some embodiments completely replaces the transport device.

[0082] The excitation device 4 is configured to generate a light signal 407 and to illuminate an illumination area 71 on the valuable or security document 3 or the security element 2 located thereon. The illumination area 71 is preferably designed as a narrow strip or rectangular area which, transverse to the spatial direction 91 along which the valuable or security document 3 and thus also the security element 2 are moved, has a larger extent than the security element 2 transverse to the spatial direction 91. This ensures that the entire security element is illuminated in each case.

[0083] However, embodiments are also possible in which the extent of the illumination area 71 transverse to the spatial direction 91 is smaller than the extent of the safety element 2 transverse to the spatial direction.

[0084] The excitation device 4 is thus arranged relative to the transport device 7 such that the light signal 407 generated by the excitation device 4, with the resulting illumination area 71, sweeps over or scans the security element 2 when the valuable or security document 3 moves. In other embodiments, the relative movement between the illumination area 71 and the security element 2 can be caused, or caused exclusively, by the optical deflection unit 119. The transport device 7 and / or the deflection unit 119 form a scanning device 138 that causes the security element 2 to be scanned by the illumination area 71.

[0085] The security element 2 comprises a pattern 110 as a security feature 100. The pattern 110 comprises several pattern areas 120. The pattern areas 120 comprise at least two different types of pattern areas. One type of pattern area is hereinafter referred to as the first pattern area 121 and the other type as the second pattern area 122. The assignment of the ordinal numbers first and second is arbitrary. In the area of ​​both the first pattern areas 121 and the second pattern areas 122, an anti-Stokes luminescent material 200 is applied to or incorporated into the security element. The anti-Stokes luminescent material 200 is preferably homogeneously distributed in the pattern areas 120, in relation to the corresponding pattern areas 120.

[0086] The anti-Stokes luminescent substance 200 is applied to the pattern areas 120 in two different ways. At least a portion of the anti-Stokes luminescent substance 200 is applied to the second pattern areas 122 in such a way that this portion is removed upon manipulation of the security element 2. For example, the portion of the anti-Stokes luminescent substance 200 that can be removed upon manipulation is applied to the security element 2 in the second pattern areas 122 by means of a water-soluble preparation, preferably by printing. The anti-Stokes luminescent substance 200 is applied to the first pattern areas 121 with a non-removable, in particular non-soluble, preparation. The anti-Stokes luminescent substance 200 applied with the non-soluble preparation is not removed from the security element 2 upon manipulation.

[0087] The anti-Stokes luminescent agent 200 is represented by hatching. Hatching from the bottom left to the top right indicates that the anti-Stokes luminescent agent 200 cannot be removed by manipulation, e.g., it is applied or introduced with a non-soluble preparation. Hatching from the top left to the bottom right, on the other hand, indicates that it can be removed by manipulation, e.g., it is applied or introduced with a soluble preparation. For better illustration, see below. Fig. 1 The first pattern areas 121 are marked with an "I" and the second pattern area 122 with an "II".

[0088] Various configurations of the first sample areas 121 and the second sample areas 122 are possible to form a sample 110. At least a portion of the anti-Stokes luminescent agent 200 can be applied to both the first sample areas 121 and the second sample areas 122 using a non-removable, in particular non-soluble, preparation. Likewise, a portion of the anti-Stokes luminescent agent 200 can also be applied to both the first sample areas 121 and the second sample areas 122 using a removable, in particular soluble, preparation.However, it is crucial that a relative proportion of the amount of anti-Stokes luminescent material 200 that can be removed from the sample area 120 by manipulation of the security element 2, in relation to the total amount of anti-Stokes luminescent material 200 in the unmanipulated state, is greater for one type of sample area 120 (here, without loss of generality, always the second sample area 122) than for the other type of sample area 120 (here always the first sample area 121).

[0089] This ensures that the surface concentrations, i.e. the amount of anti-Stokes luminescent substance 200 per area of ​​a sample area 120, the first sample areas 121 and the second sample areas 122, differ at least in the unmanipulated or manipulated state, preferably in both the unmanipulated and manipulated state.

[0090] In Fig. 2 is a schematic top view of the safety element 2 according to Fig. 1 The first sample areas 121 show a hatching pattern running diagonally from the bottom left to the top right. The second sample area 122 shows a hatching pattern running diagonally from the top left to the bottom right.

[0091] In the following, it is initially assumed that the first sample areas 121 have a surface concentration of 100 in any units of the anti-Stokes luminescent agent 200 and that this agent is completely applied with a non-removable, in particular non-soluble, preparation. The second sample areas 122, of which sample 110 in the embodiment according to Figur 1 and 2Having only one, exhibits an area concentration of 500 in the arbitrary units in the unmanipulated state. Furthermore, it is assumed that the anti-Stokes luminescent substance 200 applied in the second sample area 122 is applied with a removable, in particular soluble, preparation, so that it is removed upon manipulation of the safety element 2.

[0092] A direction of movement 93, along which the safety element 2 moves through a stationary assumed illumination area 71, is in Fig. 2 also stated.

[0093] In Figur 3a The graph shows the area concentration 95 in arbitrary units relative to the location along a longitudinal direction 111 of the safety element 2 in its unmodified state. The hatched areas below the graph also indicate, via their hatching, whether and to what extent the anti-Stokes luminescent substance 200 is applied with a non-removable, in particular non-soluble, preparation (hatching from bottom left to top right) or with a removable, in particular soluble, preparation (hatching from top left to bottom right).

[0094] In Fig. 3b is the safety element after Fig. 3a Shown in its manipulated state. It can be seen that the proportion of the removable anti-Stokes luminescent agent is completely removed (solid line) or at least almost completely removed (dashed line).

[0095] The light signal 407, generated by the excitation device 4, excites the anti-Stokes luminescent material 200 in the illumination area 71 during verification in the safety element 2. The wavelength of the excitation light of the light signal 407 lies within an excitation wavelength range. The excitation of the anti-Stokes luminescent material 200 causes it to emit luminescent light in an anti-Stokes luminescence wavelength range. The wavelengths of the anti-Stokes luminescence wavelength range are shorter than the wavelengths of the excitation wavelength range.

[0096] The anti-Stokes luminescence light 9 emitted by the activated security feature 100 of the security element 2 is detected by the detection device 5. The detection device 5 can, for example, be a spectrometer with a downstream CCD array, which allows time-resolved detection of a corresponding part of the electromagnetic spectrum. It is also possible to detect the anti-Stokes luminescence light 9 with time resolution using a photodiode 55. The detection device 5 derives an output signal 11 from the detected anti-Stokes luminescence light 9 and forwards it to the evaluation unit 6. Furthermore, another time-resolved and intensity-resolved detector can also be used.

[0097] The anti-Stokes luminescence 9 can be in the visible wavelength range, the UV wavelength range, or the IR wavelength range. Furthermore, it is possible that, in addition to the anti-Stokes luminescence, a "normal" photoluminescence also occurs in the safety element 2 when excited with the light signal 407, the luminescence wavelengths of which are greater than the wavelengths of the excitation light of the light signal 407.

[0098] To prevent interference from luminescence light of "normal" photoluminescence or from scattered excitation light of the light signal 407, some embodiments include a filter 85 which blocks wavelengths larger than those of the anti-Stokes wavelength range. This luminescence light of "normal" photoluminescence 81 is prevented by the filter 85 from reaching the detection device 5.

[0099] The security element 2 located on the security document 3 is thus excited to anti-Stokes luminescence by means of a light signal 407, the intensity of which is controlled by a predetermined input signal 27. The predetermined input signal 27 thus determines, for example via a modulation device 10, the time-varying intensity of the light signal 407.

[0100] In particular, after the intensity of the anti-Stokes luminescence light 9 has been detected, an analog-to-digital conversion can be provided in an A / D converter 118, so that an output signal 11 of the detection device 5 can be provided in digital form, for example as a data stream. The analog-to-digital conversion can also take place in the evaluation unit 6.

[0101] The evaluation unit 6 transforms the output signal 11 in a transformation module 13 by means of a characteristic function 12 into a transformed output signal 14. Such a transformation can in particular be a deconstruction of the output signal 11 with the characteristic function 12.

[0102] The transformed output signal 14 is passed to a demodulator module 15 and demodulated there. This process takes into account input signal information 16 from the light signal 407 or the input signal 27. Such input signal information 16 could be, for example, a symbolic form used to generate the input signal 27 or the light signal 407. The demodulation can be performed, for example, using an optimal filter (matched filter) that is tuned to the symbolic form.

[0103] Subsequently, a detection module 116 determines whether the detected anti-Stokes luminescence 9 was emitted by the expected anti-Stokes luminescent substance or not. If, for example, it can be determined that the transformed signal resembles a signal in which symbols are transmitted, such as when a signal-to-noise ratio above a threshold is detected, the anti-Stokes luminescent substance is recognized as genuine or as the expected anti-Stokes luminescent substance for the area for which the evaluation is currently being performed. Thus, the existence of the correct anti-Stokes luminescent substance 200 can be confirmed. This decision as to whether the correct anti-Stokes luminescent substance has been detected or not is a detection decision 18 or a component of a detection decision 18. As explained below, there are various ways in which the existence of the correct anti-Stokes luminescent substance can be confirmed.

[0104] Since the valuable or security document 3 moves together with the security element 2 relative to the illumination area 71, it is determined in a temporal sequence for different locations on the security element 2 whether the correct anti-Stokes luminescent substance 200 is present in the security element.

[0105] Based on these recognition decisions 18, which in simple embodiments only include the existence decisions, it can be determined whether the pattern 110 formed from the first and second pattern areas 121,122 corresponds to the expected pattern of an unmanipulated security element or to the expected pattern of a manipulated security element.

[0106] In its untampered state, security element 2 exhibits anti-Stokes luminescence 9 of the correct anti-Stokes luminescent substance 200 across its entire surface. However, if security element 2, which is, for example, a postage stamp, has previously been detached from a security document (e.g., another letter) and re-affixed to the security document 3 (which is also a letter), the anti-Stokes luminescent substance 200 is removed from the area of ​​the second sample area 122. Therefore, during verification, the presence of anti-Stokes luminescent substance 200 is initially detected while the illumination area covers the first sample area 121-1. Subsequently, while the illumination area 71 covers the second sample area 122, it is determined that the anti-Stokes luminescent substance 200 is no longer present.As soon as the illumination area 71 sweeps over the next first pattern area 121-2, anti-Stokes luminescence of the correct anti-Stokes luminescent material 200 is detected again. This allows a manipulated security element 2 to be reliably distinguished from an unmanipulated security element 2. If the correct anti-Stokes luminescent material 200 is missing in an area that is a pattern area 120, then the security element 2 is manipulated. Based on the detection decisions 18, the verification decision 19 can thus be derived.

[0107] Furthermore, counterfeit security element 2 can also be detected, in which the anti-Stokes luminescence 9 is caused by a different anti-Stokes luminescent substance. Although anti-Stokes luminescence is present, the transformed output signal 14 cannot then be correctly demodulated.

[0108] The evaluation unit can be used to control, for example, access restrictions such as a lock, a barrier, etc., or sorting machine 21, in which, for example, letters with manipulated postage stamps are selected. This can be done via an output unit 20, which can also output the verification result as a data record or display it visually on a display unit.

[0109] For example, a triangular pulse followed by a constant component, preferably zero, can be used as a symbolic form to encode the input signal.

[0110] It is noted that knowledge of the symbol form allows for demodulation of the transformed output signal and reconstruction of the encoded information.

[0111] It is important to note that the information encoded by the transmitted symbol(s) does not necessarily need to be determined and evaluated. In some embodiments, it is sufficient to use knowledge of the symbol shape to establish that the symbol transmission by the anti-Stokes luminescent material used corresponds to transmission by a "real" anti-Stokes luminescent material.

[0112] For example, the detection decision 18 can be derived from determining the signal-to-noise ratio in the transformed output signal 14. Thus, the presence of the anti-Stokes luminescent substance is detected, for instance, if a certain threshold of the signal-to-noise ratio is reached or exceeded.

[0113] Another alternative demodulation method is, for example, the use of an "integrate and dump" filter. Here, a discrete input signal is cumulatively summed for a specific number of samples or a predetermined time window for each step ("integrate"). After the specified number of samples has elapsed, the sum is reset to zero ("dump") and the cumulative summation process begins again. Subsequently, the information encoded in the excitation can be recovered, for example, using threshold detection. This method can generally be used when the excitation has a simple triangular pulse shape.

[0114] Another alternative and preferred method uses a Kalman filter that determines the system response at each point in time of the sampled luminescence signal and then determines the system response despite noise. Preferably, a so-called extended Kalman filter is used, i.e., a non-linear Kalman filter. Here, it is very important to fully capture the aforementioned measurement chain, since the actual input function of the Kalman filter is the excitation signal of the anti-Stokes luminescent substance. Only with correct knowledge of the excitation signal can the system response of the system, consisting of the excitation unit, safety element, and detection device, be determined.

[0115] The advantage of this method and device is that, due to integration and longer acquisition time, small nonlinearities hardly affect the evaluation, especially when using the Kalman filter. Furthermore, spectral shifts in the frequency domain of the output signal, unlike in the prior art, no longer lead to significant errors in evaluation and verification. Additionally, the DC component of the output signal no longer needs to be considered separately. Another advantage is that phase detection is no longer necessary (phase recovery is not required). Finally, the maximum possible signal-to-noise ratio is achieved.

[0116] In a particularly advantageous embodiment, the luminescent effect of the security feature is modeled as a linear time-invariant (LTI) system for short periods. This means that, to a first approximation, anti-Stokes luminescence is assumed to exhibit both linearity with respect to excitation and independence from time shifts. This simplifies the transformation equations and thus enables particularly efficient processing of the output signal.

[0117] In a particularly advantageous embodiment, it is provided that, during the evaluation process to derive the recognition decision 18, a correlation of the transformed output signal 14 with at least a part of the input signal 27 is performed in the evaluation unit, wherein the security feature (100) exhibiting anti-Stokes luminescence is deemed genuine if a correlation function reaches or exceeds a predetermined threshold value at a predetermined time or within a predetermined time range. Thus, a cross-correlation of the transformed output signal 14 with at least a part of the input signal 27 is performed. This part of the input signal can, in particular, be a symbolic form used in the input signal.

[0118] Furthermore, it may also be stipulated that the threshold must be exceeded for several predetermined time points or time ranges for the anti-Stokes luminescent substance to be considered genuine and detected. If, however, the predetermined threshold(s) are not exceeded, the anti-Stokes luminescent substance will be considered incorrect.

[0119] The characteristic function can be derived, in particular, from a reference security feature known to be genuine. Therefore, in one embodiment, the characteristic function is determined by means of a calibration measurement, wherein a reference security feature exhibiting anti-Stokes luminescence is excited and its luminescence is detected and evaluated as a reference output signal. To derive the characteristic function, a calibration measurement is thus performed, which (like the verification procedure itself) comprises exciting the reference security feature with a predetermined input signal by means of a light signal via the excitation device, detecting the luminescence emitted by the reference security feature, and converting the detected luminescence into a reference output signal by the detection device.The characteristic function is then derived from the reference output signal and the specified input signal.

[0120] In particular, in a further advantageous embodiment, it is provided that the characteristic function is the inverse of a transfer function of the reference security feature exhibiting anti-Stokes luminescence, wherein the anti-Stokes luminescence effect of the security feature and the reference security feature is considered a linear time-invariant system.

[0121] The inverse of transfer functions cannot usually be determined analytically. Therefore, in a further advantageous embodiment, the inverse of the transfer function is calculated using numerical methods. This can be done, for example, using the Matlab function "fmincon()" (e.g., in Matlab ®< Version 2016a, a software product of the company The MathWorks, Inc. in Natick, Massachusetts, USA).

[0122] Especially when using a Kalman filter, normalization can be performed during the evaluation. This normalization depends, among other things, on the detected intensity of the anti-Stokes luminescence. Therefore, the evaluation of this information can be included in the detection decision 18. In addition to determining the presence or absence of the correct anti-Stokes luminescent substance 200 in the examined scanning / illumination area 71 and the associated pattern area 120, the intensity of the detected anti-Stokes luminescence 9 is also evaluated. The intensity assigned to a pattern area 120 in this way is compared to the anti-Stokes luminescence intensities determined for other pattern areas 120 in order to derive a pattern 110.

[0123] This will be described in more detail below.

[0124] In Fig. 4a A safety element 2 with a pattern 110 is shown schematically. The pattern 110 comprises a first pattern area 121-1, a second pattern area 122-1, and another first pattern area 121-2.

[0125] The suffix "-x" is used to number sample areas 120 of a type, where x is a natural number. The first sample area 121-1, located on the left, is thus designated "-1" and is distinguished from the next first sample area "121-2" by the suffix "-2". Otherwise, the first sample areas 121-1 and 121-2 are identical with respect to the applied anti-Stokes luminescent agent 200. This means that the surface concentration of anti-Stokes luminescent agent 200 is identical in the first sample areas 121-1 and 121-2. Furthermore, the application method is the same; that is, the proportions applied with a non-removable preparation and the proportions applied with a removable preparation are also identical for both sample areas 121-1 and 121-2.

[0126] In the example shown, the entire anti-Stokes luminescent agent 200 applied in the first sample area 121, 121-1, 121-2 is applied with a non-removable, in particular non-soluble, preparation. The surface concentration is 100 arbitrary units.

[0127] On the second sample area 122, 122-1, the anti-Stokes luminescent agent 200 with a surface concentration of 500 arbitrary units is completely applied with a removable, in particular soluble, preparation. Fig. 4b The area concentration 95 is plotted against an extension of the pattern along an x-direction 92.

[0128] The first pattern area 121-1 extends from X0 to X1, the second pattern area 122-1 extends from X1 to X2, and the other first pattern area 121-2 extends from X2 to X3.

[0129] The x-direction 92 and the corresponding positions X0, X1, X2, X3 are in Fig. 4a The hatching below the function graph, which indicates the surface concentration 95 of the anti-Stokes luminescent substance 200 compared to the position in the pattern 110, indicates the proportions that are applied with non-removable preparation (hatching from top left to bottom right) or with removable preparation (hatching from bottom left to top right).

[0130] A direction of movement 93, along which the safety element 2 moves through a stationary assumed illumination area 71, is in Fig. 4a as indicated and is, for the purpose of illustrating the invention in conjunction with the further, following figures, "contrary" to the representation in Fig. 1 and 2 chosen.

[0131] In the Figuren 4a und 4b In the example shown, the anti-Stokes luminescent material 200 is applied or introduced in each of the pattern areas 120, i.e., in the first pattern areas 121-1, 121-2 and the second pattern area 122-1, either completely non-removable or completely removable.

[0132] The Fig. 4c Figure 1 shows the surface concentrations 95 of sample 110 plotted against the X-direction 92 of the safety element 2 in the manipulated state. The anti-Stokes luminescent agent 200, originally applied in the second sample area 122-1 with a removable, for example, soluble, preparation, is completely or almost completely removed (shown as a dashed line) in the manipulated state.

[0133] During verification, excitation is performed with a light signal 407. This signal is intensity-modulated. The intensity is modulated according to an input signal 27. This input signal 27, which is in Fig. 4d The schematic representation is divided into individual recurring sections 28, each section 28 representing a symbol 29. A single symbol 29 comprises an excitation component 30 and a pause component 31. In the illustrated example, these are of equal duration. The pause component 31 is preferably selected such that intersymbol interference during the transmission of the symbols via the transmission channel, which includes the safety element 2 and parts of the verification device, is avoided or at least minimized. The excitation component 30 is generally a triangular pulse comprising a linearly rising component 30A and a linearly falling component 30B, which are of equal duration and whose slopes have opposite signs.

[0134] During the excitation phase 30, the amplitude of the input signal 27 rises from 0 to a maximum amplitude 35 and then falls back to zero.

[0135] Other symbolic forms can also be used for stimulation. However, triangular stimulation elements have proven to be particularly effective.

[0136] The functional structure of the light signal 407, which is used for excitation, is identical to that of the input signal 27, since the light signal 407 is modulated with respect to its intensity according to the input signal 27. For the sake of simplicity, the maximum amplitude value (the maximum amplitude 35) of a symbol represented in the input signal 27 or modulated onto the light signal will be used below as the amplitude of the input signal 27 and the amplitude of the light signal 407, respectively, which is used to excite the safety element.If excitation occurs with a light signal 407 in which symbols with the same maximum amplitude 35 of the excitation component 30 are encoded iteratively via modulation, then in the simplified representation the amplitude of the light signal 407 is represented as a constant value that corresponds to the maximum amplitude of the excitation component 30 of the respective symbols. If the intensity of the light signal 407 is increased, this is equivalent to a corresponding increase in the maximum amplitude of the symbols encoded in the light signal 407.

[0137] In Fig. 4e The graph shows the intensity of the excitation light signal 407 versus time. As mentioned above, the intensity is represented by the maximum amplitude 35 of the excitation component of the transmitted symbols in this graph. For the sake of simplicity, an intensity curve reflecting the symbol shape is not shown. The graph shows the times TX0 to TX3, which correspond to the times at which positions X0 to X3 pass through the illumination area 71.

[0138] In Figur 4f For an intact, untampered security element, the anti-Stokes luminescence intensity 96, measured without adjusting the excitation light signal, is greatly simplified and presented neglecting transient processes, intensity fluctuations due to modulation, intersymbol interference, or similar factors. Fig. 4g A corresponding normalization value 97, determined based on the detected intensities, is specified, which would normalize a received symbol to a unit intensity at the corresponding detected intensity of the anti-Stokes luminescent light. It is always assumed that the safety element 2 scans equally sized areas of the pattern regions 120 through the illumination region 71.If, for example, the surface concentration of anti-Stokes luminescent substance 200 in the illumination area 71 of the swept pattern area 121 is 100 in any units, then, after capturing the generated luminescence and decongesting it with the characteristic function assigned to the anti-Stokes luminescent substance 200, and performing a corresponding demodulation, a normalization value 97 of, for example, 50 in any units is set as the value by which the total intensity of the symbol must be divided to normalize a received symbol to a standard intensity. If the surface concentration then increases, for example, because at a later time the second pattern area 122 with a surface concentration of 500 in any units of surface concentration of anti-Stokes luminescent substance 200 is located in illumination area 71, then the generated luminescence increases, and consequently, so does the intensity.An area below the curve described by the symbol. To normalize this area to the unit area, i.e., to bring the intensity to the standard intensity, a normalization value of, for example, 97 out of 250 in any normalization units is now necessary. It thus becomes clear that the intensity of the received demodulated signal, or a normalization value in the evaluation, is each a measure of the combination of the area concentration of the anti-Stokes luminescent agent 200 and the excitation intensity of the light signal 407.

[0139] An increase in the intensity of the light signal 407 also leads to an increase in the resulting intensity of the anti-Stokes luminescent light. This makes it possible to utilize the transmitted intensity to identify, based on the normalization intensity 97, the pattern areas 120 along the spatial direction 91, which is parallel to the direction of movement 93 of the safety element through the illumination area, taking into account the temporal sequence and the relative movement of safety element 2 and illumination area 71 or light signal 407.

[0140] In addition, the evaluation also provides information on whether the correct anti-Stokes luminescent substance 200 is present in the corresponding sample area. If this is not the case, correct symbol transfer does not occur, and therefore the normalization value cannot be determined. Depending on the evaluation method used, the anti-Stokes luminescence intensity can be determined with finer or coarser temporal resolution, and from this, the existence of the correct, i.e., expected, anti-Stokes luminescent substance and its surface concentration can be determined with finer or coarser spatial resolution. This then allows the security element 2 to be structured into different sample areas 120, and the resulting sample 110 can be identified, for example, by comparison with target data or other expert knowledge about correct, intact, and manipulated security elements 2.

[0141] It is also possible that the intensity increases so significantly due to a change in the surface concentration that a measuring range is exceeded in which linear intensity detection by the detection device 5 is possible. In this case, the detection device 5 is said to be saturated. In the saturated state, a correct determination by evaluation based on the characteristic function is no longer possible in such a way as to determine whether the correct anti-Stokes luminescent agent 200 is present in the corresponding area of ​​the safety element or not. Therefore, it is advantageous to dynamically adjust the intensity of the light signal 407 by adjusting the input signal so that the achieved luminescence intensity also returns to the linear measuring range of the detection device.

[0142] To reliably check sample areas for the presence of the correct anti-Stokes luminescent substance 200, it is advantageous if a plurality of symbols are transmitted in the light signal while the illumination area 71 scans over a sample area 120. A preferred minimum number is 5 symbols.

[0143] Even during the transmission of the first symbol, when the detection device 5 becomes saturated by the luminescence of the anti-Stokes luminescence 9, the intensity of the light signal 407 for the subsequent transmitted symbol can often be reduced by a correct amount. This is because the time interval between reaching the upper threshold of the linear measurement range and falling below this threshold again provides a rough measure of the maximum anti-Stokes luminescence intensity achieved during excitation. This holds true at least when there is no excessive intersymbol interference. It should be noted that the excitation, even if the graphical representation does not show this, always fluctuates between zero and the depicted maximum symbol intensity.

[0144] If intersymbol interference is extremely strong, a larger number of transmitted symbols are required to correctly reduce the excitation intensity. Depending on the intersymbol interference occurring, the symbol transmission rate used via the light signal 407, and the relative speed used between the light signal 407 and the safety element 2, a setting must be found that enables a reliable and correct evaluation of the individual pattern areas 120 of the safety element 2.

[0145] In Fig. 4h, 4i und 4j are the input signal 27 ( Fig. 4h ), which is identical to light signal 407 except for a factor and other units, as well as the greatly simplified anti-Stokes luminescence light intensities 96 for an untampered security element ( Fig. 4i ) and a manipulated security element ( Fig. 4jThe schematic representation shows the case where the maximum amplitude 35 in the input signal 27 is adapted to the expected increase in intensity for an intact, untampered security element in the time range between TX1 and TX2. The input signal is again simplified to represent only the maximum amplitude of the transmitted symbols. The actual modulation of the input signal 27 and the resulting light signal 407 are not shown. In this time range between TX1 and TX2, the maximum amplitude 35 is reduced to 1 / 5 of its original value in the time range between TX0 and TX1. In the time range between TX2 and TX3, the maximum amplitude 35 is increased again to its original value.

[0146] In the unmanipulated state, the anti-Stokes luminescence intensity 96 is constant throughout the entire measurement. In the manipulated state, the anti-Stokes luminescence intensity 96 drops to 0 when the anti-Stokes luminescent substance is completely removed and is significantly reduced when it is partially removed.

[0147] It is understood by those skilled in the art that only exemplary embodiments of patterns and possible area concentrations are shown here. Reference symbol list

[0148] 1 Device 2 Safety element 3 Safety document 4 Excitation device 5 Detection device 6 Evaluation device 7 Transport device 8 Luminescent light 9 Anti-Stokes luminescence 10 Modulation device 11 Output signal 12 Function 13 Transformation module 14 Output signal 15 Demodulator module 16 Input signal information 17 Control device 18 Detection decisions 19 Verification decision 20 Output device 21 Sorting machine 27 Input signal 28 Sections 29 Symbol 30 Excitation component 30A Increasing component 30B Decreasing component 31 Pause component (Non-excitation component) 35 Maximum amplitude 55 Photodiode 71 Illumination area 81 Photoluminescence 85 Filter 91 Spatial direction 92x direction 93 Direction of movement 94 Detection direction 95 Area concentration (function graph of) 96 Anti-Stokes luminescence intensity 100 Safety feature 110 Pattern 111 Longitudinal direction 116 Detection module 118 A / D converter 119 (Optical) deflection unit 120 Pattern areas 121, 121-1x first pattern area 122,122-x second sample area 138 scanning device 200 anti-Stokes luminescent material 401 light source 407 light signal,

Claims

1. Method for verifying security elements (2), wherein a security element (2) comprises a pattern (110) formed from pattern areas (120) as a security feature (100), wherein the pattern areas (120) comprise at least one or several first pattern areas (121, 121-x) and one or several second pattern areas (122, 122-x), wherein one and the same anti-Stokes luminescent substance (200) is present both in the one or the several first pattern areas (121, 121-x) and in the one or the several second pattern areas (122, 122-x) in an unmanipulated state of the security element (2), wherein the anti-Stokes luminescent substance is excited by a light signal whose wavelength or wavelengths lie within an excitation wavelength range, exhibits anti-Stokes luminescence in an anti-Stokes wavelength range, wherein the one or the several second pattern areas (122, 122-x) each differ from the one or the several first pattern areas (121, 121-x) in a way that a relative proportion of the anti-Stokes luminescent substance (200) removable from the corresponding pattern area (120) upon manipulation is greater for the second pattern area or the several second pattern areas (122, 122-x) than for the respective first pattern areas (121, 121-x) or the respective several first pattern areas (121, 121-x), comprising the steps of: Generating a light signal (407) which is intensity-modulated over time in accordance with an input signal (27) and whose wavelength or wavelengths lie in the excitation wavelength range, and radiating the light signal (407) into a limited illumination area (71); providing one of the security elements (2); moving said one of the security elements (2) relative to the illumination area (71) so that the illumination area sweeps over at least two different ones of the pattern areas (120) of the graphic pattern (110) of the security element (2) over time; iteratively detecting luminescent light in the anti-Stokes wavelength range and converting it into an output signal (11) which represents an intensity of the detected luminescent light, transforming the output signal (11) by means of at least one provided characteristic function (12) for an expected anti-Stokes luminescent substance (200) by an evaluation device (6) into a transformed output signal (14), evaluating the transformed output signal (14), taking into account at least one input signal information (16) of the input signal (27), for deriving recognition-decisions (18) for the anti-Stokes luminescent substance (200) by the evaluation device (6), deriving a verification decision based on the recognition-decisions (18) and outputting the verification decision (19) by the evaluation device (6).

2. Method according to claim 1, characterized in that deriving the detection decisions comprises determining the existence of the expected anti-Stokes luminescent substance (200) and a luminescence intensity which can be assigned to the expected anti-Stokes luminescent substance, which is a measure of the amount of the expected anti-Stokes luminescent substance (200) in the illumination area.

3. Method according to claim 1 or 2, characterized in that the evaluation comprises creating a verification pattern on the basis of the detection decisions derived in temporal sequence, taking into account the movement of the illumination area (71) relative to the security element (2), and the verification decision (19) is derived based on a comparison with a predetermined authenticity or forgery pattern.

4. Method according to one of the preceding claims, characterized in that the light signal (407) is modulated in time such that symbols (29) are transmitted iteratively.

5. Method according to one of the preceding claims, characterized in that the relative movement of the illumination area (71) and the security element (2) at a speed and the modulation of the light signal (407) are coordinated with each other, taking into account an extension of the pattern areas (120) parallel to the relative direction of movement (93), that the anti-Stokes luminescent substance (200) is excited with a minimum number of symbols modulated onto the light signal during the relative movement of the illumination area over the respective pattern area, the minimum number being greater than two.

6. Method according to one of the preceding claims 4 to 5, characterized in that the detection is carried out at a frequency which is greater by a factor of 20, preferably by a factor of 100 or more, than a symbol modulation frequency at which symbols are modulated onto the light signal (407).

7. A device (1) for verifying security elements (2) according to one of the claims 8 to 15, comprising a pattern (110) formed of pattern areas (120) as a security feature (100), wherein the pattern areas (120) comprise an anti-Stokes luminescent substance (200),wherein the device (1) comprises: a control device (17) for generating an input signal (27), an excitation unit (4) for generating a light signal (407) temporally intensity modulated in accordance with the input signal (27), the wavelength or wavelengths of the light signal being in the excitation wavelength range, and for irradiating the light signal (407) into a limited illumination area (71), a scanning device (138) coupled to the control device (17) for moving one of the security elements (2) according to one of the claims 8 to 15 relative to the illumination area (71), so that the illumination area (71) sweeps over different ones of the at least two pattern areas (120) of the graphic pattern (110) of the security element (2) over time; a detection device (5) for iteratively detecting luminescent light (8) in the anti-Stokes wavelength range and converting it into an output signal (11) which represents an intensity of the detected luminescent light, and an evaluation device (6) which comprises a transformation module (13) for transforming the output signal (11) by means of at least one characteristic function (12) provided into a transformed output signal (14) and is designed for evaluating the transformed output signal (14), to derive recognition decisions (18) for the anti-Stokes luminescent substance (200) when evaluating the transformed output signal (14), taking into account at least one input signal information (16) of the input signal (27), and to derive a verification decision (19) based on the recognition decisions (18), and an output device (20) for outputting the verification decision (19) of the evaluation device (6).

8. Security element (2) with a pattern (110) formed from pattern areas (120) as a security feature (100), the pattern areas (120) comprising at least a first pattern area (121, 121-x) and a second pattern area (122, 122-x), wherein the first pattern area (121, 121-x) and the second pattern area (122, 122-x) having an anti-Stokes luminescent substance (200) in an unmanipulated state of the security element (2), which, upon excitation with a light signal (407) having wavelengths in an excitation wavelength range, exhibits luminescence in an anti-Stokes wavelength range, wherein the first pattern area (121, 121-x) and the second pattern area (122, 122-x) differ in that a proportion of the anti-Stokes luminescent substance (200), which can be removed from the security element (2) during manipulation, is greater in the second pattern area (122, 122-x) than in the first pattern area (121, 121-x).

9. Security element (2) according to claim 8, characterized in that the pattern (110) comprises a plurality of first pattern areas (121-x) of the same type as the one first pattern area (121-1) and / or a plurality of second pattern area (122-x) of the same type as the one second pattern area (122-1).

10. Security element (2) according to one of the claims 8 or 9, characterized in that the surface concentrations of the anti-Stokes luminescent substance (200) in the first pattern area (121) and in the second pattern area (122) are the same in the non-manipulated state.

11. Security element (2) according to one of the claims 8 or 9, characterized in that the surface concentrations of the anti-Stokes luminescent substance (200) in the first pattern area and in the second pattern area, which are not removable, are the same.

12. Security element (2) according to any one of the claims 8 to 11, characterized in that the areal concentrations of the anti-Stokes luminescent substance (200) in the first pattern area (121) and in the second pattern area (122) are unequal in the non-manipulated state and the areal concentrations of the anti-Stokes luminescent substance (200), which are removable, in the first pattern area (121) and in the second pattern area (122) are also unequal.

13. Security element (2) according to one of the claims 8 to 12, characterized in that the anti-Stokes luminescent substance (200) of the second pattern area (122) is not completely removable during the manipulation.

14. Security element (2) according to one of the claims 8 to 13, characterized in that a detection direction (94) exists with respect to which the first pattern areas (121) and second pattern areas (122) occur alternately in the pattern and the first and the last pattern area (120) along the detection direction (94) are either a first pattern area (121) or a second pattern area (122), respectively.

15. Security element (2) according to one of the claims 8 to 14, characterized in that the pattern (110) comprises one or several pattern areas (120) that are different from the first pattern areas (121) and the second pattern areas (122) and contain the anti-Stokes luminescent substance (200).

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