EP3866126A1 - Method for verifying a smartphone-verifiable security feature, smartphone-verifiable security feature and valuable or security document - Google Patents

Abstract

The invention relates to a method for checking a smartphone-verifiable security feature, with optical excitation of a phosphor of a security feature (1), which consists at least partially of the phosphor, by means of a light source of a smartphone (7); Detecting a luminescence of the phosphor, which the phosphor emits on the optical excitation, by means of an image acquisition device (9) of the smartphone (7); and evaluating image recordings of the security feature (1) that are recorded during the decay time by means of the image recording device (9), by means of an evaluation device of the smartphone (7) and using one or more software applications that are installed on the smartphone (7) so that they can run are. The evaluation comprises determining electronic information that is encoded in a machine-readable code, which is part of the security feature (1) and at least partially consists of the phosphor; Determining an optical parameter for the luminescence in the frequency and / or the time domain; and comparing the optical parameter with a reference parameter in order to check the authenticity of the security feature (1). In addition, a smartphone-verifiable security feature and a value or security document with a smartphone-verifiable security feature are disclosed.

Description

The invention relates to a method for checking a smartphone-verifiable security feature, a smartphone-verifiable security feature and a value or security document.

background

It is known from the prior art to use security features equipped with luminescent substances (phosphors) for the protection and authentication of documents of value and security documents. They are mostly used as so-called level 2 features. Their presence can be detected via the emission of the phosphors, which can be excited with simple hand-held devices (UV or IR radiation sources) and which usually takes place in the visible spectral range. In addition, such security features are used for copy protection. On the other hand, luminescent security features equipped with a particularly high level of protection against forgery are also used as level 3 features that can be read out by machine. The authenticity verification of such features is usually associated with a high level of technical effort.

In the area of security and value documents as well as in the area of product protection, there is increasing interest in the use of authenticity features that have a high security level (level 2+ or level 3 characteristics) but are less technical Have the effort checked.

From the document WO 2012/083469 A1 a device for authenticating documents marked with photochromic systems is known. The photochromic security feature shows a change in color and / or a change in shape under the action of a flash light excitation. It is further described that the security feature is based on a retinal protein.

The document WO 2013/034471 A1 describes a device for recognizing a document which has a phosphor-based security feature with so-called wavelength conversion properties. For this purpose, a light generating device (for example an LED flash unit), which irradiates the security feature with excitation light, and an image recording device (for example a digital camera) are provided of a mobile communication device), which is to receive the light emitted by the security feature. It has been shown, however, that the phosphors used regularly have decay times which do not allow an evaluation of the emission with widely used devices, in particular an authenticity check with the aid of commercially available smartphones.

The document WO 2013/034603 A1 describes a method for verifying a security document with a security feature in the form of a fluorescent printing element. The method provides for the printing element to be excited by means of a light source, so that it emits electromagnetic radiation as a result of this excitation, which can be detected in a further step by means of a sensor. The recorded data is evaluated by comparing it with specified data. The verification result is output in a further step depending on the result of the comparison. In particular, the method is to be carried out with a smartphone, the flashlight module of the smartphone being used as the excitation source and the photo sensor of the camera of the smartphone being used as the detection unit. Inorganic phosphors, namely nitridic phosphors, europium-doped alkaline earth orthosilicate and alkaline earth oxyorthosilicate phosphors, cerium-doped rare earth metal aluminum gallium garnet phosphors, red light emitting (Ca, Sr) S: Eu ^{2+, are mentioned as phosphors for the pigment-like fluorescent printing element} and green light emitting SrGa2S4: Eu ²⁺ . The proposed phosphors are so-called LED conversion phosphors which decay extremely quickly. It has been shown, however, that it is practically impossible to reliably detect the luminescence signals of these rapidly decaying phosphors directly during the flash light excitation, because the luminescence signals have a far too low intensity compared to the excitation light and are covered by the intense, stimulating flash light of the smartphone .

In the practical application of the phosphors described in the aforementioned prior art, two hitherto unsolved problems have emerged. These previously known phosphors are regularly used as so-called conversion phosphors for the production of white LEDs, so that these phosphors are also regularly contained as radiation-converting components in the flashlight LEDs of commercially available smartphones. This means that the excitation radiation of the smartphone flash light units used as the excitation source has a high probability of having the same luminescence signals as are expected from the security feature to be examined. A sure one Proof of authenticity of the value and security documents equipped with such security features is excluded for this reason alone.

A second problem arises from the fact that the phosphors named in the prior art for use as security features generally have just as short decay times in the ns to microsecond range as are also applicable to the flash LED for the reasons mentioned . When excited with the flash of a smartphone, the emissions originating from the security feature are either completely superimposed by the flash or they have already subsided before the image is recorded.

summary

The object of the invention is to create a method for checking a smartphone-verifiable security feature, a smartphone-verifiable security feature and a value or security document that have a security feature with extended functionality.

To solve this, a method for checking a smartphone-verifiable security feature according to independent claim 1 is created. Furthermore, a smartphone verifcable security feature and a value or security document according to the independent claims 13 and 14 are created. Refinements are the subject of dependent subclaims.

According to one aspect, a method for checking a smartphone-verifiable security feature is provided, in which the following is provided: optical excitation of a phosphor of a security feature, which consists at least partially of the phosphor, by means of a light source of a smartphone; Detecting a luminescence of the phosphor, which the phosphor emits on the optical excitation, by means of an image acquisition device of the smartphone; and evaluating image recordings of the security feature that are recorded during the decay time by means of the image recording device, by means of an evaluation device of the smartphone and using one or more software applications that are installed on the smartphone so that they can run. The evaluation of the image recordings of the security feature comprises the following: determining electronic information that is encoded in a machine-readable code, which is part of the security feature and at least partially consists of the phosphor; Determine an optical parameter for the luminescence in the frequency and / or the time domain; and comparing the optical parameter with a reference parameter in order to check the authenticity of the security feature.

According to a further aspect, a smartphone-verifiable security feature is created which has the following: a luminescent material which can be optically excited by means of a light source of a smartphone to emit luminescence, the luminescence being detectable by an image detection device of the smartphone by means of image recordings; and a machine-readable code consisting at least partially of the phosphor.

Furthermore, a value or security document with such a smartphone-verifiable security feature is provided.

On the one hand, the proposed technology enables an authenticity check for the security feature by means of a commercially available smartphone. In addition, the machine-readable code encompassed by the security feature creates the possibility of providing (additional) electronic information that can also be read using the functionalities of the smartphone. The electronic information can be used for an extended authenticity check when checking the security feature. However, the alternative or additional provision of electronic information, which is only used partially or not at all for checking authenticity, can also be provided.

The technical components provided with the (commercially available) smartphone are used to carry out the process. The fluorescent material is prepared so that its optical properties enable the security feature to be checked using a smartphone. This includes in particular the decay behavior of the luminescence emitted by the phosphor (light emission) when it is optically stimulated by the light source of the smartphone. The envisaged decay time allows the smartphone to detect a sufficient number of image recordings by means of the image acquisition device in order to determine the security feature for the verification, which takes place in particular on the basis of the optical parameter of the luminescence. This can be an optical parameter in the frequency and / or time domain. The frequency domain relates to frequency-dependent properties of the luminescence. In contrast, time-dependent optical properties of the luminescence are assigned to the time domain.

The smartphone can have a camera as the image capturing device. The light source is set up to emit light pulses, for which purpose a flash LED (light-emitting diode) can be used, for example. The decay time provided for the luminescence of the luminescent material makes it possible, despite the simple or limited optical image recording capability of the smartphone due to the small size, to capture images of sufficient quality so that the optical parameter of the luminescence can be determined and evaluated for checking the authenticity of the security feature .

Another aspect of the solution is that a security feature is equipped with a specific phosphor which circumvents the problems described above. The luminescent material is configured, on the one hand, to be excitable with a light source of the smartphone or a similar mobile data processing device, that is to say in particular a flashlight LED of a smartphone. At the same time, the luminescent material has such a luminescence characteristic that it is possible to detect the luminescence signals with a high degree of certainty even after the excitation process has ended with the aid of the image acquisition unit of the same smartphone (mobile data processing device). In addition to a high efficiency of the spectral excitability and a high luminescence yield, this requires above all a decay time of the phosphor that is adapted to the exceptional speed of the image acquisition unit of the smartphone.

A reliably evaluable security feature is provided which allows exclusive luminescence properties such as the spectral emission and decay characteristics of the special phosphors used to create the security feature to be included in the test as authenticity criteria. In addition, it can be provided that the decaying luminescence signals of the security feature are not visible to the human eye either during or after the end of the excitation. It has been shown that the options for providing suitable phosphors for realizing the solution shown are rather limited. This applies in particular to the required decay characteristics.

The luminescence of the phosphor emitted in response to the optical excitation can have a decay time in the range from 1 ms to 100 ms.

Provision can be made to determine electronic information that is encoded in a multi-dimensional machine-readable code in which the luminescence has a first optical parameter and a second optical parameter, which of the first optical parameter is different. The multi-dimensionality of the machine-readable code can be provided and implemented, for example, in that the luminescence in different areas or components of the machine-readable code of the security feature is different in color. As an alternative or in addition, the decay times for the luminescence can differ in different areas or components of the machine-readable code. For this purpose, it can be provided that the luminescent material is a mixture of several emitter materials (luminescent materials). Different areas of the machine-readable code can also consist of different emitter materials, each of which has decay times in the range from 1 ms to 100 ms. Such machine-readable codes are also referred to as three-dimensional codes.

The electronic information can be encoded in a one- or multi-dimensional QR code with which the machine-readable code of the security feature is formed. The QR code can be a two- or a three-dimensional QR code. In connection with the three-dimensional QR code, the explanations given above in connection with the multi-dimensional machine-readable code regarding different optical parameters apply accordingly.

When evaluating the image recordings, the electronic information can be compared with electronic reference information in order to check the authenticity of the security feature. In this embodiment, the electronic information that is read from the machine-readable code as part of the evaluation of the image recordings is used in addition to the optical parameter (or several optical parameters) to check the authenticity of the security feature. In this or other embodiments, the electronic information can include, for example, personal information, in particular when the authenticity of an identification document is checked by checking the security feature.

The smartphone can have an executable installed software application which is set up to determine a decay time for the luminescence from the image recordings and to compare the decay time of the luminescence with a reference decay time as an optical parameter for the luminescence in the time domain. The smartphone is set up here by means of the software application to examine the decay behavior of the luminescence in a time-resolved manner and from this to determine the decay time of the luminescence. The decay behavior of materials (phosphors), i.e. the decrease in the intensity of a stimulus emitted luminescence is often described using a simple exponential function: I = I ₀ e ^{- (t / τ)} . The decay constant τ contained therein denotes the period of time up to which the intensity of the luminescence has fallen to about 37% of the initial intensity after the excitation source has been switched off. The decay behavior of the phosphor can also be exponential several times, with several time constants τ contributing to the decay curve.

The smartphone can have an executable installed software application that is set up to determine a spectral parameter for the luminescence from the image recordings and to compare the spectral parameter for the luminescence as an optical parameter in the frequency domain with a spectral reference parameter. In this embodiment, the optical parameter relates to a spectral (frequency-dependent) property of the luminescence, that is to say, for example, luminescence components of different wavelengths. The spectral parameter can relate to light emission at one or more different wavelengths, for example.

The electronic information can be determined indicating the optical parameter for the luminescence. In this embodiment, the electronic information that is determined when the machine-readable code of the security feature is read out indicates the optical parameter or parameters of the luminescence that are used for the authenticity check, for example a decay time of the phosphor. For example, it can be provided that, by means of the machine-readable code, the decay time for the luminescence of the luminescent material is stored in encoded form in the security features. As an alternative or in addition, the machine-readable code can contain one or more spectral parameters for the luminescence of the phosphor encoded.

The electronic information can be determined indicating cryptographic information. Cryptographic information can include, for example, one or more cryptographic keys that can be used, for example, for asymmetric cryptography, for example for subsequent data communication using the smartphone. Alternatively or in addition, the electronic information can include a serial number of a product on which the security feature is arranged. A signed identification number can also be part of the electronic information that is determined by evaluating the machine-readable code.

When evaluating image recordings, it can be determined whether a last of the image recordings is free of luminescence of the luminescence of the security feature, and it can be provided that the security feature is only determined as genuine if the last of the image recordings is free of luminescence of the phosphor. If, when evaluating the image recordings, it is found that the last of the image recordings does show (a remainder of the) luminescence of the phosphor, the security feature is determined to be not genuine.

For reading out or determining the electronic information, only one or more image recordings can be evaluated for which a presence of the luminescence of the luminescent material of the security feature was determined. Alternatively or in addition, the electronic information can be determined from one or more image recordings that are free from the luminescence of the phosphor of the security feature.

Provision can be made to check a security feature which has at least one material from the following group as a phosphor: (Ca _{1-xy CexMn y} ) ₃ (Sc _1-z / Mn _z ) ₂ Si ₃ O ₁₂ ; with 0 <x ≤ 0.1; 0 <y ≤ 0.8; and 0 <z ≤ 0.8; and y / z ≈ 2; and Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ .

^{Ce 3+} - and Mn ²⁺ - codoped silicate garnet phosphors (CSS), which are described with the formula: Ca _a Sc ₂ Si3O ₁₂ : Ce ³⁺ , Mn ^2+, have proven to be a particularly suitable phosphor class for the security feature can be. Such phosphors are distinguished by a high absorption strength at 450 nm, a high luminescence intensity and an efficient energy transfer between the Ce ³⁺ and the Mn ²⁺ ions. According to an alternative notation, the phosphor can be described with the formula: (Ca _1-x- Ce _x ) ₃ (Sc _1-z Mn _z ) ₂ Si ₃ O ₁₂ , this being often assumed on the basis of the known ion radii in the specialist literature It is found that the Ce ³⁺ ions are preferably incorporated on Ca ²⁺ and the Mn ²⁺ ions preferably on Sc ³⁺ lattice positions.

In experimental investigations it was surprisingly found that phase-pure, highly efficient and particularly stable Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ phosphors are formed above all if it is assumed when calculating the initial weights of the starting materials that the Mn ²⁺ ions are incorporated into the lattice ^{on both Ca 2+} and Sc ^{3+ sites.} Particularly good results are achieved if the weight calculations are based on the assumption that about 75% of the Mn ²⁺ coactivators replace the Ca ²⁺ and about 25% ^{replace the Sc 3+} ions as lattice components.

The phosphor can particularly preferably be described by the following general chemical formula: (Ca _1-xy Ce _x Mn _y ) ₃ (Sc _1-z Mn _z ) ₂ Si ₃ O ₁₂ with 0 <x 0.1; 0 <y 0.8; 0 <z 0.8; a y / z ratio of ≈ 2 is preferred. Taking the stoichiometric factors into account, this corresponds to the ratio given for the occupation of the Ca ²⁺ or Sc ³⁺ lattice sites by Mn ²⁺ coactivator ions.

With the Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ materials described, particularly advantageous phosphors are provided which have emissions with decay times between 5 ms and 30 ms and whose luminescence signals are used with high reliability even after the end of the flash excitation the camera modules of commercially available smartphones can be detected.

The emission spectra of the proposed phosphors each consist of three bands, those of the direct luminescence of the Ce ³⁺ activator ions (band with a λ _max of about 505 nm), as well as the ^{emissions made possible by the Ce 3+} - Mn ²⁺ energy transfer on the different Lattice sites positioned Mn ²⁺ coactivators can be assigned. The maxima of the last-mentioned emission bands are around 570 nm (Mn ²⁺ on Ca ²⁺ place) and around 700 nm (Mn ²⁺ on Sc ³⁺ place).

The relative intensities of the different emission bands can be varied and adjusted via the concentrations of the activator and coactivator ions and via the respective concentration ratios. In addition, the individual emissions have different spectral decay times. While the decay time of the quantum mechanically permitted Ce ³⁺ emission is in the nanosecond range, decay times in the single-digit (Mn ²⁺ on Ca ²⁺ space) or double-digit millisecond range ^{for the two Mn 2+} emission bands resulting from quantum-mechanically forbidden optical transitions (Mn ²⁺ on Sc ³⁺ place) reached.

The fact that the emission bands encountered in the green spectral range with maxima at around 505 nm and 570 nm overlap to a pronounced degree due to their comparatively large half-widths, also leads to an overlapping of the decay curves of these emissions. Nevertheless, the modified CSS phosphors are characterized by different spectral decay curves with distinguishable decay times. On the other hand, this constellation results in the case that the entire visible spectral range is detected in the decay measurements, a significant color shift of the decaying luminescence of the phosphors results. It has also been shown that the individual emission bands have no mono-exponential decay curves due to their characteristic overlays. Rather, bi- or tri-exponential decay curves are characteristic.

The special decay behavior described contributes to a large extent to the exclusivity of the Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ phosphors. In addition, there are other properties that these phosphors recommend for use in luminescent security features, the presence and authenticity of which can be verified with the aid of commercially available smartphones. On the one hand, the luminescent substances are practically non-excitable in the ultraviolet spectral range and, on the other hand, the body color of the corresponding luminescent pigments is such that they are easily adapted or adapted to the color designs of the security and value documents to be protected (banknotes, ID cards, passports, driver's licenses, etc.). can be covered by the printing inks used to produce these documents. This means that the presence of the CSS: Ce ³⁺ , Mn ²⁺ phosphors introduced as a security feature in the security documents cannot be recognized by the viewer either with the naked eye or with the aid of conventional UV excitation sources.

It can be provided that, upon UV excitation, effectively luminescent, rapidly decaying phosphors are added to the phosphors with delayed decay behavior which emit almost exclusively in the visible spectral range, preferably at 450 nm. The stationary photoluminescence of the corresponding additional components, which is clearly perceptible upon UV excitation, can serve as a security-increasing masking of the security features integrated in the security documents.

Even if the options for providing the phosphors required to implement the solution shown are severely limited, there are, in addition to the Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ phosphors, a few other materials that, due to their Decay behavior could be used to produce the proposed security feature.

The table below summarizes some of the phosphor compositions that have been tested for their suitability, including the luminescence properties relevant for the application. link λ _em [nm] Decay time τ [ms] Luminescence yield Excitability at 450 nm Ce ³⁺ / Eu ³⁺ -, Mn ³⁺ - co-activated compounds high Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ³⁺ 470-900 5-30 strong Ca ₃ Sc ₂ Ge ₃ O ₁₂ : Ce ³⁺ , Mn ³⁺ 470-850 5- 15 weak Sr ₃ SC ₂ Ge ₃ O ₁₂ : Ce ³⁺ , Mn ³⁺ 470-800 3- 15 moderate Ca ₉ MgNa (PO ₄ ) ₇ : Eu ³⁺ , Mn ³⁺ 500-750 ∼ 26 weak - moderate BaMg ₂ Si ₂ O ₇ : Ce ³⁺ , Mn ³⁺ , Dy ³⁺ 570-800 5-10 weak - moderate BaMg ₂ Si ₂ O ₇ : Mn ³⁺ , Dy ³⁺ 570-800 ∼ 5 weak CaSiO ₃ : Eu ³⁺ , Mn ³⁺ 550-700 10-20 weak - moderate Ca ₂ P ₂ O ₇ : Eu ³⁺ , Mn ³⁺ 400-660 10-20 weak Cr ³⁺ - activated compounds high ZnGa ₂ O ₄ : Cr ³⁺ , Bi ³⁺ 650-770 5 - 10 moderate Zn ₃ Ga ₂ SnO ₈ : Cr ³⁺ , Bi ³⁺ 660-820 1 - 5 moderate Mn ⁴⁺ activated compounds high BaGeF ₆ : Mn ⁴⁺ ∼ 634 ∼ 6 moderate K ₂ SiF ₆ : Mn ⁴⁺ ∼ 631 ∼ 8 moderate - strong

In particular, the table contains information on the measured maxima of the respective emission bands and on the decay times. Verbal scaling was used to evaluate the luminescence yield and the spectral excitability at 450 nm.

The luminescent substances listed are essentially Ce ³⁺ and Mn ²⁺ codoped silicate garnets or germanate garnets, ^{activated with Mn 2+} ions and, if necessary, additionally with certain rare earth ions (Ce ³⁺ , Eu ^{2 +} , Dy ³⁺ ) co-activated complex silicate or phosphatic basic lattices, around Cr ³⁺ - activated gallate compounds and around the Mn4 + - activated phosphors BaGeF6: Mn4 + and K2SiF6: Mn4 +. This listing has no final character. It can be assumed that further suitable phosphors are also available for realizing the security feature in its various configurations.

In this context, it is to be regarded as extremely advantageous to modify phosphors that appear suitable by deliberately changing their chemical composition, ie by deliberately made substitutions in the cation and / or anion sublattice, so that their luminescence properties, in particular their characteristic decay times, become clear differ from the data described in the specialist literature. In this way, the exclusivity of the delayed decay luminescent materials and the forgery-proofness of the corresponding security features can be increased significantly.

By checking the security feature, the authenticity of a value or security document on which the smartphone-verifiable security feature is arranged can be checked.

The configurations explained above in connection with the method for checking the smartphone-verifiable security feature apply accordingly in connection with the smartphone-verifiable security feature and the value or security document.

In another example, a method for checking a security feature on an article or an object, in particular a value or security document, is provided, the method having the following steps: optical excitation of a phosphor of a security feature which is arranged on an article or object and consists at least partially of the phosphor, by means of a light source of a smartphone; Detecting a luminescence of the phosphor, which the phosphor emits on the optical excitation, by means of an image acquisition device of a portable test device, wherein the luminescence can have a decay time in the range from 1 ms to 100 ms, for example; and evaluating image recordings of the security feature that are captured during the decay time by means of the image acquisition device, by means of an evaluation device of the portable test device and using one or more software applications that are installed and run on the portable test device. The evaluation includes the following: Determination of electronic information that is encoded in a machine-readable code, which is part of the security feature and at least consists partly of the phosphor; Determining an optical parameter for the luminescence in the frequency and / or the time domain; and comparing the optical parameter with a reference parameter in order to check the authenticity of the security feature. The portable test device can be any hand-held device which is set up to provide light for the optical excitation of the phosphor and to record the image recordings. Not only value and security documents can be checked for authenticity by verifying the security feature, but also any other articles or objects on which the security feature is applied with the machine-readable code. The test device then also allows the (additional) electronic information that is encoded in the machine-readable code, which in turn is part of the security feature, to be read out.

Description of exemplary embodiments

Fig. 1

eine schematische Darstellung einer Ausführungsform eines Sicherheitsmerkmals auf einem Sicherheitsdokument in Gestalt einer Banknote;

Fig. 2

eine schematische Darstellung von Komponenten einer Anordnung zur Verifikation des Sicherheitsmerkmals;

Fig. 3

eine schematische Darstellung des An- und Abklingverhaltens eines Leuchtstoffes des Sicherheitsmerkmals bei Blitzlichtanregung;

Fig. 4

eine schematische Darstellung für ein Verfahren zum Überprüfen eines smartphoneverifizierbaren Sicherheitsmerkmals der Verifikation des Sicherheitsmerkmals;

Fig. 5

ein Anregungsspektrum der 700 nm Emissionsbande eines Leuchtstoffes gemäß Ausführungsbeispiel 1;

Fig. 6

ein Emissionsspektrum der bei 450 nm angeregten stationären Photolumineszenz des Leuchtstoffes gemäß Ausführungsbeispiel 1;

Fig. 7

spektrale Abklingkurven der unterschiedlichen Emissionsbanden eines im Ausführungsbeispiel 1 beschriebenen Leuchtstoffes;

Fig. 8

eine Farbverschiebung der über den gesamten sichtbaren Spektralbereich detektierten, abklingenden Lumineszenz des Leuchtstoffes gemäß Ausführungsbeispiel 1, dargestellt anhand des zeitlichen Verlaufes der x-y-Farbkoordinaten in der CIE-Normfarbtafel;

Fig. 9

Emissionsspektren der stationären Photolumineszenz der bei 450 nm angeregten Leuchtstoffe gemäß der Ausführungsbeispiele 2 und 3; und

Fig. 10

Abklingkurven der Hauptemissionsbanden der bei 450 nm angeregten Leuchtstoffe gemäß der Ausführungsbeispiele 2 und 3;

In the following, further exemplary embodiments are explained in more detail with reference to figures of a drawing. Show it:

Fig. 1

a schematic representation of an embodiment of a security feature on a security document in the form of a bank note;

Fig. 2

a schematic representation of components of an arrangement for verification of the security feature;

Fig. 3

a schematic representation of the rise and fall behavior of a luminescent material of the security feature in the event of flash light excitation;

Fig. 4

a schematic representation of a method for checking a smartphone-verifiable security feature of the verification of the security feature;

Fig. 5

an excitation spectrum of the 700 nm emission band of a phosphor according to embodiment 1;

Fig. 6

an emission spectrum of the stationary photoluminescence of the phosphor excited at 450 nm according to embodiment 1;

Fig. 7

spectral decay curves of the different emission bands of a phosphor described in embodiment 1;

Fig. 8

a color shift of the decaying luminescence of the phosphor according to embodiment 1 detected over the entire visible spectral range, shown on the basis of the time course of the xy color coordinates in the CIE standard color table;

Fig. 9

Emission spectra of the stationary photoluminescence of the phosphors excited at 450 nm according to embodiments 2 and 3; and

Fig. 10

Decay curves of the main emission bands of the phosphors excited at 450 nm in accordance with exemplary embodiments 2 and 3;

Fig. 1 shows a security feature 1 which is applied to a value document, namely a symbolized security document 2 in the form of a bank note. The security feature serves to prove the authenticity of the security document 2. The security feature 1 here has a star shape. It is positioned below a visible feature 3, in this case the nominal value of the bank note. The security feature 1 consists of a luminescence which can be excited by means of the lighting unit of a smartphone, preferably in the blue spectral range, to luminescence decaying in the ms range, as described above.

Fig. 2 shows a schematic representation of an arrangement for the verification of the security feature 1, the security feature 1 being excited to luminescence by means of a lighting unit 4 of an image recording unit 6 of a mobile terminal, namely a smartphone 7, by the lighting unit 4 with excitation light, in particular white LED flash light 8 a spectral maximum of about 450 nm is generated. The flash light 08 has an intensity IA. During the excitation, the luminescent material of the security feature 1 emits stationary electromagnetic radiation in the visible spectral range, which decays in the ms range after the end of the excitation. The decaying emission IE of the phosphor is detected with a camera 9 of the image recording unit 06 of the smartphone 7 by triggering a series or video recording. Furthermore, the camera 9 working as a detector detects an ambient radiation I0 of the daylight or room light which strikes the security feature 1 and the bank note 2 and is reflected there. The influence of the ambient radiation I0 can be kept low during the method in that a distance d between the security feature 1 and the smartphone 7 is kept small. Due to the small distance d , which is preferably below the focus area of the image recording unit 6, the smartphone 7 largely shields the ambient radiation I0. This is because no sharp image recordings are required for the reliable verification of the diffuse luminescence signals of the security feature.

Fig. 3 shows a schematic representation of the rise and fall behavior of the phosphor that is used in the security feature 1. In the diagram, an emission curve 11 of the security feature 1 excited to luminescence is shown along a time axis t. Furthermore, a flash excitation curve 12 is plotted along the time axis. If the single flash is triggered using the smartphone 7 ( Fig. 2 ), the LED flash excitation curve increases 12 rises steeply, holds its level for a short time and then drops to zero in the ns to µs range. The fluorescent material of the security feature 1 is excited to luminescence by the electromagnetic radiation of the flashlight, with its emission curve 11 rising almost at the same time as the flashlight excitation curve 12. The emission of the luminescent material 11 decays significantly more slowly after the end of the flash light excitation 12 than the excitation radiation of the lighting unit of the smartphone, which is preferably equipped with white emitting LEDs. The decay time of the phosphor is in the ms range.

Below the timeline are in Fig. 3 individual by the detector 9 of the smartphone 7 ( Fig. 2 ) captured images 13 of the security feature 1 are shown. The image recordings 13 show the decaying emission intensity of the security feature 1 on the basis of the brightness of the star pattern used by way of example, which decreases over time. After the emission of the phosphor has essentially completely subsided, a reference image 14b can be recorded as the last image of the recorded image sequence. Depending on the evaluation method, an additional reference image 14a (start image) can also be recorded before the activation of the excitation radiation (triggering of the flash). Optionally, to ensure the availability of a reference image required for calculating the image differences, a start image 14a can be recorded as an additional reference image before the series or video recordings that are decisive for the detection of the decaying luminescence signals of the security feature are triggered.

Fig. 4 FIG. 11 shows a schematic illustration of a method for checking a smartphone-verifiable security feature, for example using the arrangement from FIG Fig. 2 . In step 40, a phosphor of the security feature 1, which consists at least partially of the phosphor, is optically stimulated by means of a light source of the smartphone 1, the light emitted by the lighting unit 4 being radiated onto the security feature 1, for example in the form of a or multiple flash pulses. The phosphor reacts to this excitation by means of luminescence (step 41). In step 42, one or more image recordings are captured or recorded by means of the camera 9 of the smartphone 7. The luminescence of the phosphor decays accordingly with a decay time. In one embodiment, the image recordings comprise at least one image record which is essentially free of the luminescence of the phosphor.

In step 43, the image recordings of the security feature 1, which are recorded during the decay time by means of the camera 9 forming an image recording device, are made with the aid of an evaluation device of the smartphone 7 and using one or more Software applications that are installed and ready to run on the smartphone 7 are evaluated. For this purpose, the evaluation device of the smartphone 7 has at least one processor to which a local data memory can be assigned. The evaluation of the image recordings can take place entirely locally in the smartphone 7 or, alternatively, comprise partial steps for data processing that are carried out on an external computing device (not shown), for example a remote server. For this purpose, the smartphone can exchange data with the external computing device, in particular via a wireless data communication connection.

When evaluating the image recordings, electronic information is determined which is encoded in a machine-readable code, which is part of the security feature 1 and at least partially consists of the phosphor. The electronic information can be encoded in a one-dimensional or multi-dimensional QR code with which the machine-readable code of the security feature 1 is formed. The QR code can be a two- or a three-dimensional QR code. Software applications for evaluating (reading out) such machine-readable codes are known as such in various designs.

The electronic information can then be stored in the local memory of the smartphone 1 and / or an external memory (not shown).

The evaluation of the image recordings also includes determining an optical parameter for the luminescence of the phosphor in the frequency and / or time domain. For example, the decay time of the phosphor is determined from the image recordings. This can be carried out on the basis of the image recordings, which represent a temporal sequence of image recordings after the optical excitation, so that the temporal course of the luminescence is documented in the electronic image data in an evaluable manner. The optical parameter determined in this way is then compared with a reference parameter in order to check the authenticity of the security feature 1. For this purpose, the reference parameter is stored in the local memory of the smartphone, for example.

The determination of the optical parameter can be carried out in the context of an emission analysis. Here, the recorded image series can be compared with reference recordings, for example to determine difference images. In addition to the calculation of the image differences and their analysis, methods of image processing such as contrast adjustment and histogram analysis of the different color channels can be used to selectively reduce both the spectral emission as well as to verify the exclusive decay characteristics of the phosphor used. By comparing the calculated / determined optical parameters with the authenticity / comparison parameters of the security feature 1, which are preferably stored in the data memory of the smartphone 7, the authenticity of the checked security document can be confirmed in a step 44. In particular, by verifying the security feature 1 on the security document, the authenticity and integrity of the security document can be confirmed.

Fig. 5 shows an excitation spectrum 121 of the 700 nm emission band of a phosphor according to embodiment 1. To produce this phosphor, 0.2822 g CaCO ₃ , 0.5335 g Sc ₂ (C ₂ O ₄ ) ₃ · 10.723H ₂ O, 0.1803 g SiO ₂ , 0.0052 g CeO ₂ , and 0.0358 g MnC ₂ O ₄ · 2H ₂ O completely homogenized by pestle with the addition of acetone. After the solvent has evaporated, the dry powder mixture is transferred to a corundum crucible. The sample is first pre-calcined in a chamber furnace at 500 ° C. for 2 hours in an air atmosphere and then annealed in a tube furnace at 1400 ° C. for 4 hours in a 5% H ₂ /95% N ₂ atmosphere. The resulting product is then sieved. This phosphor has the formula (Ca _2.82 Ce _0.03 Mn _0.15 ) (Sc _1.95 Mn _0.05 ) Si ₃ O ₁₂ . The excitation spectrum makes it clear that the exemplary inventive phosphor has a maximum spectral excitability in the range from 440 to 450 nm.

Fig. 6 shows a corresponding emission spectrum 111 of the phosphor according to embodiment 1 at 450 nm excitation. It is found that the phosphor specially configured via the phosphor composition and the selected preparation conditions has broadband emissions over the entire visible spectral range. Three emission bands with maxima at about 505 nm, 570 nm and about 700 nm are visible, the band with a maximum of about 700 nm having the highest relative intensity. As already described, these bands of the direct luminescence of the Ce ³⁺ activator ions (Ce ³⁺ on Ca ²⁺ place), as well as the ^{emissions of the Mn 2} positioned on the different lattice sites made possible ^{by the Ce 3+} - Mn ^{2+ energy transfer, can be seen +} Assign coactivators (Mn ²⁺ on Ca ²⁺ place or Mn ²⁺ on Sc ³⁺ place).

Fig. 7 shows the spectral decay curves of the individual emission bands. Curve 1311 is the decay curve for the 505 nm emission, curve 1312 is the decay curve for the 570 nm emission, and curve 1313 is the decay curve for the 700 nm emission. It can be clearly seen that the spectral decay curves for the individual emissions differ significantly. As already explained, is for the emission with a maximum of about 505 nm a decay in the nanosecond range was found, while the luminescence bands with maxima of about 570 or about 700 nm have decay times in the single-digit or double-digit millisecond range. It is also apparent to a person skilled in the art that there is a high probability that the individual decay curves will not run exponentially. Rather, the measured curves seem to have multi-exponential decay characteristics.

Fig. 8 illustrates the color shift that results when the decaying luminescence is detected over the entire visible spectral range. The Fig. 8 first a schematic representation of a CIE standard color table of the CIE standard valence system. The CIE standard valence system was defined in 1931 to establish a relationship between human color perception and the physical causes of the color stimulus and typically covers the entirety of all perceivable colors, with color perception referring to that of a defined normal observer. Every color or every emission spectrum of a self-luminous substance is represented in the CIE standard value table by a single xy coordinate. The color coordinates of the luminescence signals, which are integrally measured as a function of the decay time, are shown in FIG Fig. 8 represented by the elements with the reference numerals 140 to 147. At the same time, the data determined for a phosphor according to exemplary embodiment 1 can be taken from the table below. Reference number Decay time in ms Color coordinates x y 140 0 0.385 0.528 141 1 0.515 0.472 142 10 0.521 0.465 143 20th 0.534 0.453 144 30th 0.554 0.432 145 40 0.577 0.407 146 50 0.595 0.385 147 60 0.603 0.374

The color shift, which tends to lead from the green to the red spectral range, results from the superposition of the Fig. 6 emission bands shown as well as from the differences and the superimposition of the corresponding in the Fig. 7 The decay curves of the phosphor according to embodiment 1 shown here. The special decay behavior described contributes to a large extent to the exclusivity of the Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ phosphor.

Fig. 9 FIG. 11 shows the emission spectra 1123, 113 of the stationary photoluminescence of the phosphors excited at 450 nm in accordance with exemplary embodiments 2 and 3. Fig. 10 shows the associated decay curves 132, 133 of the main emission bands of the phosphors excited at 450 nm in accordance with exemplary embodiments 2 and 3.

To produce the phosphor according to embodiment 2, 0.2898 g CaCO ₃ , 0.1362 g Sc ₂ O ₃ , 0.1803 g SiO ₂ , 0.0130 g Ce (NO ₃ ) ₃ · 6H ₂ O, 0.0179 g are used MnC ₂ O ⁴ · 2H ₂ O and 1.8170 g of tris (hydroxymethyl) aminomethane were completely dissolved in a mixture of 10 ml of nitric acid and 100 ml of water while stirring and heating on a hot plate. The liquid is then evaporated until the remaining gel ignites and a black foam forms. This foam is first dried in a drying cabinet at 150 ° C., then finely ground in a mortar and transferred to a porcelain crucible. In a first heating step, the mixture is calcined for 2 hours at 1000 ° C. in the air atmosphere of a chamber furnace for the purpose of decomposing residual organic constituents. The annealing material, which now has a white body color, is then mixed with two percent by mass of boric acid and this time annealed again for 4 hours at 1300 ° C. in a 5% forming gas atmosphere. The resulting phosphor has the composition (Ca _2.895 Ce _0.03 Mn _0.075 ) (Sc _1.975 Mn _0.025 ) Si ₃ O ₁₂ . The curve 112 in the Fig. 9 shows the emission spectrum of this phosphor. In the Fig. 10 the curve 132 denotes the decay curve for this phosphor which preferably emits in the green spectral range.

To produce the phosphor according to embodiment 3 with the composition (Ca _2.745 Ce _0.03 Mn _0.225 ) (Sc _1.925 Mn _0.075 ) Si ₃ O ₁₂ , 0.2747 g CaCO ₃ , 0.1327 g Sc ₂ O ₃ , 0.1803 g SiO ₂ , 0.0130 g Ce (NO ₃ ) ₃ · 6H ₂ O, 0.0537 g MnC ₂ O ₄ · 2H ₂ O and 1.8170 g tris (hydroxymethyl) aminomethane with stirring and heating in a mixture of 10 ml of nitric acid and 100 ml of water dissolved. The liquid is then evaporated until I ignite the resulting gel. The resulting black foam is dried in a drying cabinet at 150 ° C., then finely ground in a mortar and transferred to a porcelain crucible. After a first two-hour annealing at 1000 ° C in the air atmosphere of a chamber furnace and the subsequent admixing of two percent by mass of boric acid to the cooled annealing material, another four-hour thermal treatment takes place at 1100 ° C in a 5% forming gas atmosphere. That measured at 450 nm excitation The emission spectrum of the phosphor obtained is shown in curve 113 Fig. 9 shown, the associated decay curve is curve 133 of FIG Fig. 10 refer to.

The two exemplary embodiments and the associated figures show once again with great clarity that the Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ phosphors are a particularly suitable class of phosphors for the formation of a security feature. By varying the phosphor composition and the preparation conditions, numerous exclusive phosphor compositions with different decay behavior and distinguishable emission spectra and, for this reason, with a high level of security and authenticity can be created. The exclusive properties of the phosphors that can be used to protect valuable and security documents in the form of security features can be reliably verified with the help of commercially available smartphones.

The features disclosed in the above description, the claims and the drawing can be important both individually and in any combination for the implementation of the various designs.

List of reference symbols

1

Security feature

2

Security document / banknote

3

Face value

4th

Lighting unit

6th

Image acquisition unit

7th

Smartphone

8th

Flashlight

9

Camera / detector

11

Emission curve

12th

Flash excitation curve

13th

Image recording of the security feature 01

14a

Start screen

14b

Reference image

15th

CIE normal color table

40 - 43

Procedural steps

111

Emission spectrum of the phosphor according to embodiment 1

112

Emission spectrum of the phosphor according to embodiment 2

113

Emission spectrum of the phosphor according to embodiment 3

121

Excitation spectrum of the phosphor according to embodiment 1

1311

Decay curve for the 505 nm emission of the phosphor according to embodiment 1

1312

Decay curve for the 570 nm emission of the phosphor according to embodiment 1

1313

Decay curve for the 700 nm emission of the phosphor according to embodiment 1

132

Decay curve of the predominantly green emission of the phosphor according to embodiment 2

133

Decay curve of the predominantly green emission of the phosphor according to embodiment 3

140-147

x-y color coordinates of the decaying integral luminescence of the phosphor according to embodiment 1

Claims (14)

Method for checking a smartphone-verifiable security feature, with - Optical excitation of a luminescent material of a security feature (1), which consists at least partially of the luminescent material, by means of a light source of a smartphone (7); - Detecting a luminescence of the phosphor, which the phosphor emits on the optical excitation, by means of an image acquisition device (9) of the smartphone (7); and - Evaluation of image recordings of the security feature (1) that are captured during the decay time by means of the image capturing device (9), by means of an evaluation device of the smartphone (7) and using one or more software applications that are installed on the smartphone (7) so that they can run are, comprising: - Determination of electronic information which is encoded in a machine-readable code, which is part of the security feature (1) and at least partially consists of the phosphor; - Determining an optical parameter for the luminescence in the frequency and / or the time domain; and - Comparing the optical parameter with a reference parameter in order to check the authenticity of the security feature (1). Method according to Claim 1, characterized in that electronic information is determined which is encoded in a multidimensional machine-readable code in which the luminescence has a first optical parameter and a second optical parameter which is different from the first optical parameter. Method according to Claim 1 or 2, characterized in that the electronic information is encoded in a one-dimensional or multi-dimensional QR code with which the machine-readable code of the security feature (1) is formed. Method according to at least one of the preceding claims, characterized in that when evaluating the image recordings, the electronic information is compared with electronic reference information in order to check the authenticity of the security feature (1). The method according to at least one of the preceding claims, characterized in that the smartphone (7) has an executable installed software application which is set up to determine a decay time for the luminescence from the image recordings and as an optical parameter for the luminescence in the time domain Compare the decay time of the luminescence and a reference decay time. The method according to at least one of the preceding claims, characterized in that the smartphone (7) has an installed, executable software application which is set up to determine a spectral parameter for the luminescence from the image recordings and the spectral parameter as an optical parameter in the frequency domain for luminescence and to be compared with a spectral reference parameter. Method according to at least one of the preceding claims, characterized in that the electronic information is determined indicating the optical parameters for the luminescence. Method according to at least one of the preceding claims, characterized in that the electronic information is determined to be indicative of cryptographic information. The method according to at least one of the preceding claims, characterized in that when evaluating the image recordings it is determined whether a last of the image recordings is free of luminescence of the phosphor of the security feature (1) and the security feature (1) is only determined as genuine if the the last of the image recordings is free from the luminescence of the phosphor. The method according to at least one of the preceding claims, characterized in that a security feature (1) is checked which has at least one material from the following group as a luminescent material: - (Ca _1-xy Cex Mn _y ) ₃ (Sc _1-z / Mn _z ) ₂ Si ₃ O ₁₂ ; with 0 <x ≤ 0.1; 0 <y ≤ 0.8; and 0 <z ≤ 0.8; and y / z ≈ 2; and Ca ₃ Sc ₂ Si ₃ O ₁₂ : Ce ³⁺ , Mn ²⁺ . Method according to at least one of the preceding claims, characterized in that by checking the security feature (1) the authenticity of a value or security document on which the smartphone-verifiable security feature (1) is arranged is checked. Method according to at least one of the preceding claims, characterized in that the luminescence of the phosphor emitted in response to the optical excitation has a decay time in the range from 1 ms to 100 ms. Smartphone-verifiable security feature, with - A luminescent material which can be optically excited by means of a light source (4) of a smartphone (7) to emit luminescence, the luminescence being detectable by an image recording device (9) of the smartphone (7) by means of image recordings; and - A machine-readable code, which consists at least partially of the phosphor. Value or security document with a smartphone-verifiable security feature according to claim 13.

Images