RU2567068C1 - Determination of laminar article authentication - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: claimed invention consists in authentication of laminar article including the cattier with concealed protective marking produced with the help of luminescence bonding with crystalline structure based on yttrium oxysulphide activated by ytterbium and cerium ions, or holmium and cerium ions, or ytterbium and holmium ions. In compliance with one version, protective marking sections are subjected to constant exciting radiation in spectral band of 930-970 nm to register the source luminescence level. Then, protective marking sections are subjected to constant exciting radiation in spectral band of 330-370 nm to suppress optically the aforesaid luminescence at invariance of its spectral composition. Exciting radiation is withdrawn and, after recovery of luminescence intensity, article authentication is established. In compliance with another version, protective marking sections are subjected to pulse or variable exciting radiation in spectral band of 930-970 nm to register luminescence radiation intensity in build-up or extinction phase. Then, protective marking sections are subjected to constant exciting radiation in spectral band of 330-370 nm to register luminescence radiation intensity variation in build-up or extinction phase.

EFFECT: efficient expert or machine authentication of protective attribute on various documents including securities.

7 cl 1 tbl, 3 ex

Description

The invention relates to multilayer products from various materials using phosphors, including paper, polymer, and to the field of protection of products from counterfeiting and is intended for instrumental determination of the authenticity of protected printing products, such as banknotes and letterhead paper, labels, excise and postage stamps , payment and identification documents, as well as passports and travel documents.

Recently, with increasing competition among manufacturers of security printing products, as well as a steady increase in the technical capabilities of potential counterfeiters, complex security features have become increasingly relevant. By such protective features it is customary to understand technical solutions in which, during instrument control, authenticity is checked not one but two or more parameters related in a specified way or a certain reaction to two or more simultaneously specified actions is evaluated.

Examples of such parametric effects include the dependence of the UV luminescence of a substance on the temperature applied to it, or the angle of rotation of the plane of polarization of linearly polarized radiation under the influence of an external electric field, or a reversible color change of a substance under the influence of heat and light.

The difficulty in creating such signs often lies in the need to reliably evaluate the parameters of interest of the sign under heterogeneous exposure under conditions of a limited time interval or with a small content of the measured substance with the simultaneous presence of interfering factors (interference), i.e. with a small signal to noise ratio.

On the other hand, to complicate the chemical and / or elemental control of substances included in the protective label, it is necessary to minimize their weight (percentage) amount in the total composition. In addition, a frequent requirement for security features for instrument and machine authentication is their secrecy, that is, hardly detectable by generally accessible methods. In this regard, practical interest in creating complex security features is primarily represented by solutions that do not exhibit their properties in the visible range of the spectrum, which significantly complicates the task.

These contradictions and a wide range of generally available substances known from the prior art and available on the market determine the need to search and create new protective features of an integrated principle of action.

The proposed solution is based on the well-known physical phenomena of photostimulation (“flash”) and optical quenching of photoluminescence, which are fundamental in nature and are described below.

Inorganic compounds having photostimulated quenching of luminescence in the visible spectrum are known from the prior art. Examples of their compositions are shown in table 1.

Among the presented compounds, the compositions of ZnS — Cu, Me, Cl, should be classified as practically important, where Me = Co ²⁺ for quenching and Me = Pb ²⁺ , Sm ^3+, or Mn ²⁺ for flash. Studies of infrared sensitivity spectra, flash spectra (green for Pb ²⁺ , red for Sm ³⁺ and orange for Mn ²⁺ ), as well as the kinetics of afterglow of visible luminescence, showed that these compounds work according to the following scheme:

where e _c is the electron in the conduction band, ap _v is the hole in the valence band.

The amount of light accumulated in such luminescent compounds under optimal conditions of UV excitation reaches 10 ¹⁴ -10 ¹⁵ quanta · cm ^-2 , i.e. commensurate with the total number of impurity centers at the penetration depth of the exciting radiation (~ 50 μm for λ _exc = 365 nm and C _Cu ≈3 · 10 ¹⁷ cm ^-3 ). At the same time, the efficiency of ZnS - Cu, Me, Cl luminescent compounds is limited primarily by incomplete absorption of the recorded luminescent radiation, which is no more than 10-15%.

Thus, the currently known optically sensitive luminescent compounds based on zinc sulfide are designed to detect only quenching of visible luminescence when exposed to radiation in the region from 0.7 to 2.7 μm. The main disadvantage of these compounds, which completely excludes the possibility of their use as luminescent compounds with photostimulated quenching of luminescence upon excitation by radiation in the range from 0.7 to 2.7 μm and stimulation by UV radiation, is the absence of ions in their composition that provide, when excited by radiation in the range from 0.7 to 2.7 μm, Stokes or anti-Stokes IR luminescence in the specified area.

In this regard, to solve this problem, new classes of compounds have been developed that provide photostimulated quenching of the luminescence obtained by excitation in a given region of the spectrum due to radiation exposure in the wavelength range from 350 to 650 nm.

Let us consider the physical prerequisites for the possibility of synthesizing such luminescent compounds.

The effect of optical quenching by infrared radiation of the visible luminescence of inorganic compounds based on zinc sulfide is explained in the literature on the basis of a simplified zone model. In this model, IR quenching of luminescence is associated with the release of holes with emission centers ionized by UV radiation into the valence band, followed by their nonradiative recombination at the emission centers formed by specially introduced impurity quenching ions. The situation basically remains the same if the quencher is not a hole trap, but a deep electron trap. Here the recombination interaction of impurity centers occurs, which usually have effective charges of opposite signs. A hole freed by thermal vibrations migrates from the center of luminescence to the quenching center that has captured the electron and recombines with it. In addition, the role of quenching centers can play small electronic traps. With decreasing temperature, the time spent by electrons in them increases, and therefore the possibility of recombination of the latter with holes increases. The degree of quenching, that is, the fraction of nonradiative transitions, depends on the density of the excitation power. As in the case of the interaction of two luminescence centers, this is explained by the fact that with increasing intensity of the exciting radiation, the recombination rate grows faster (proportionally to N _a · n - where N _{a is the} number of ionized centers, n is the number of free electrons) than the rate of hole release from ionized extinguishing centers. As a result, the quenching effect changes. The degree of quenching also depends on the duration of the stimulating radiation pulses (τ). Obviously, if the pulse duration (τ) is less than the time of hole capture at the ionized emission centers, then the holes will not have time to return to the above centers.

From the above it follows that the necessary conditions for the creation of luminescent compounds with photostimulated quenching (“modulation”) of luminescence when exposed to UV radiation in the wavelength range of 300-650 nm are as follows:

- the presence of rare-earth ions or their pairs (for example, Yb - Ho) in the composition of the compounds, which, when excited by laser radiation in the range from 370 to 1550 nm, provide Stokes and anti-Stokes IR luminescence in the region of 700-2500 nm;

- the presence in the composition of compounds of ions forming donor levels in the band gap (deep electron traps) with a low probability of release of the electrons located on them. The formation of such traps can be achieved by partial heterovalent substitution of cations of the pigment matrix by other ions having a large electron capture cross section;

- the presence in the pigment of ions that form acceptor levels (deep hole traps) in the band gap of the pigment crystal. The formation of this type of traps can be achieved by partial heterovalent substitution of cations of the pigment matrix by other ions having a large hole capture cross section.

By selecting quenchers or sensitizers spatially located near the luminescence centers, it is possible to purposefully organize channels for selecting charge carriers from the luminescence centers or vice versa of the inflow. In both cases, modulation of stationary photoluminescence is observed (negative - quenching, positive - synergistic flaring). Moreover, when applying only electromagnetic oscillations corresponding to the frequency (wavelength) of the change in signal intensity, luminescence is not observed at all.

Using this approach, it is possible to synthesize luminescent compounds with modulation of stationary Stokes and anti-Stokes luminescence based on inorganic substances - sulfides, oxides, oxysulfides, phosphates, composite compounds of alkaline-earth, rare-earth elements having both recombination and intracenter luminescence mechanisms.

The prior art solution is US 4387112 A, describing a technical solution that uses for instrument control the authenticity of valuable documents inorganic luminescent compounds with rare earth ions having anti-Stokes luminescence in the visible spectrum.

At the present stage, this solution does not provide the necessary level of security due to the availability of these luminescent compounds in the free market. Also, this solution does not have the property of changing the intensity of luminescent radiation when exposed to stimulating radiation.

Also known is the solution US 4047033 A, which describes a technical solution for instrumental verification of the authenticity of a valuable document based on the use of inorganic compounds with rare earth ions based on the Sr S compound having flare (photostimulated) luminescence in the visible range of the optical spectrum.

This solution relies on luminescent compounds widely known in the art. Its significant drawback is also the use of the visible range of the spectrum when recording a feature.

Closest to the proposed invention is a method of protecting documents, securities or products using nanodiamonds with active NV centers. This solution is based on the use of complex effects - changes in the intensity of photoluminescence under the influence of a microwave field (RU 2357866).

The disadvantage of this method is the intrinsic photoluminescence of nanodiamonds in the visible spectrum, and the depth of modulation of its intensity by the microwave field is small, which requires the use of highly sensitive methods of analysis, high concentrations of the substance and exposure to the document by intense fields.

The objective of the proposed invention is to increase the level of security, providing the possibility of expert or machine determination of the authenticity of the product based on the use of the security feature of the integrated principle of operation.

The problem is solved by the method of determining the authenticity of a multilayer product containing a carrier with a hidden protective marking deposited on its surface, the marking of which is performed using a luminescent compound with a crystalline structure based on yttrium oxysulfide activated by ytterbium and cerium ions, or holmium and cerium ions, or ions ytterbium and holmium, while the areas of the protective marking are exposed to constant exciting radiation in the spectral range of 930-970 nm, f CSIRO sink luminescence level, then produce a constant effect stimulating radiation in the spectral range of 330-370 nm and a fixed optical quenching of said luminescence at an invariance its spectral composition, relieve stimulating recovery after radiation and luminescence intensity establish the authenticity of the product. The action of the exciting radiation is produced by sequentially changing the wavelength of the stimulating radiation, the dependence of the intensity of the luminescent radiation on the wavelength of the stimulating radiation is fixed, the effect of the exciting radiation is fixed, the level of luminescence is fixed, the effect of the stimulating radiation is changed, the power of the stimulating radiation is changed, the dependence of the intensity of the luminescent radiation on the intensity of the stimulating radiation. If a change in the luminescence intensity is detected in the protective marking areas treated with stimulating radiation, a latent image and / or information is recorded.

The problem is also solved by the method of determining the authenticity of a multilayer product containing a carrier with a hidden protective marking deposited on its surface, the marking of which is made using a luminescent compound with a crystalline structure based on yttrium oxysulfide activated by ytterbium and cerium ions or holmium and cerium ions, or ytterbium and holmium ions, while the areas of the protective marking are exposed to pulsed or variable exciting radiation in the spectral in the range of 930–970 nm, the intensity of luminescent radiation is recorded in the phase of acceleration or attenuation, they are exposed to pulsed or variable stimulating radiation in the spectral range of 330-370 nm, the change in intensity of luminescent radiation is recorded in the phase of acceleration or attenuation. After exposure to exciting radiation, the temporal parameters of luminescence in the phase of acceleration or attenuation are additionally fixed, and after exposure to stimulating radiation, a change in the temporal parameters of luminescence in the phase of acceleration or attenuation is recorded. If a change in the luminescence intensity is detected in the protective marking areas treated with stimulating radiation, a latent image and / or information is recorded.

The advantages of the proposed invention are based on the use of a complex feature of authenticity, consisting in a certain reaction to a double exposure to the material of the protective labeling and not appearing in other generally available materials (imitators) known from the prior art.

Also in the field of instrument control for determining the authenticity of valuable documents, technical solutions are of particular interest, which can use certain information about the document being verified and are not only inaccessible to the potential counterfeiter, but also hidden from the public.

If some non-random information is applied to the protective marking, it is necessary to ensure its safety at least during the period of authentication, and at most during the period of circulation of the product. In this regard, the most promising is the application of protective information, which is temporary in nature. For example, information can be applied to the product for use in a short period of time, that is, it is applied and stored on the product only during its verification cycle on a counting and sorting machine or at an ATM. After checking the information, it can naturally disappear, for example, being destroyed by the action of environmental components (temperature, humidity, pressure, magnetic fields, light, etc.).

One of the options for implementing the proposed invention is to increase the level of security, providing the possibility of expert or machine authentication, with the possibility of multiple verification of the authenticity of the product, eliminating the inadvertent detection of hidden information between verification cycles.

The problem is solved by the method of authenticating the product, which consists in detecting changes in the luminescence intensity of the composite material in the areas of protective markings treated with stimulating radiation, and latent image and / or information thus applied are recorded.

The advantages of the proposed invention are based on the use of a complex feature of authenticity, consisting in a certain reaction to a double exposure to the material of the protective labeling and not appearing in other generally available materials (imitators) known from the prior art.

An additional condition is the possibility of applying and reading hidden information, which is randomly generated, but appears and is read using double exposure directly in the process of machine control and, therefore, cannot be reproduced consciously.

Example 1

The product in the form of a banknote contains on the front side a colorless protective marking of a rectangular shape made by the offset printing method.

The protective marking contains 80% of a binder and 20% of an inorganic luminescent compound based on yttrium oxysulfide activated by ytterbium and cerium in the form of particles from 2 to 5 μm in size.

When processing areas of protective markings with exciting pulsed laser radiation in the range of 930–970 nm, the Stokes luminescence of ytterbium ions is observed in two main spectral bands in the range of 0.98–1.02 nm.

When exposed to areas of protective markings with stimulating radiation in the spectral range of 330-370 nm, optical quenching of the indicated luminescence is observed, the luminescence intensity changing according to a given law depending on the intensity of the stimulating radiation, and only the intensity of the spectral bands of luminescence, and not its spectral composition, changes.

After removal of stimulating UV radiation, the luminescence intensity is restored.

Thus, the totality of the measured parameters, including the luminescence spectrum, the dependence of the intensity of the spectral bands not only on the exciting, but also on the modulating radiation can be instrumentally measured, and thus the authenticity of the banknote is established.

Example 2

The product in the form of an excise stamp contains on the front side a colorless protective marking of a rectangular shape made by offset printing.

The protective marking contains 80% of a binder and 10% of an inorganic luminescent compound based on yttrium oxysulfide activated by holmium and cerium in the form of particles ranging in size from 1 to 3 microns.

When processing areas of protective markings with exciting pulsed laser radiation in the range of 930–970 nm, the Stokes luminescence of holmium ions is observed in the main spectral band of 1.18 nm with a luminescence acceleration rate characterized by a time constant of 1 ms.

When exposed to areas of protective markings with stimulating radiation in the spectral range of 330-370 nm, optical quenching of the indicated luminescence is observed. In this case, only the intensity of the luminescence spectral band and the rate of its acceleration and attenuation, but not its spectral composition, varies according to a given law depending on the intensity of the stimulating radiation.

After removal of the stimulating UV radiation, the luminescence intensity is restored, and the spectral band acceleration and attenuation rates, which are characterized by the luminescence time constant, take the previously indicated initial value.

Thus, the totality of the measured parameters, including the luminescence spectrum, the dependence of the intensity of the spectral bands not only on the exciting, but also on the modulating radiation, as well as the change in the rate of rise and decay of the luminescence depending on the intensity of the modulating radiation, can be instrumentally measured, and thus established the authenticity of the product.

Example 3

A method for checking the authenticity of a product in the form of a banknote that contains on the front side a colorless protective marking of a rectangular shape made by the offset printing method.

The protective marking contains 80% of a binder and 20% of an inorganic luminescent compound based on yttrium oxysulfide activated by ytterbium and cerium in the form of particles from 2 to 5 μm in size.

When the protective marking surface is continuously treated with exciting pulsed laser radiation in the range of 930–970 nm, the Stokes luminescence of ytterbium ions is observed in two main spectral bands in the range of 0.98–1.02 nm.

When some areas of the protective marking are stimulated by selective exposure in the spectral range 330-370 nm, optical quenching of the indicated luminescence is observed, and the luminescence intensity changes according to a given law depending on the intensity of the stimulating radiation, and only the intensity of the spectral bands of luminescence changes, and not its spectral composition .

During selective exposure to stimulating radiation, a random code is generated on the marking surface, which can be read out in the process of determining the authenticity of a banknote.

After removing the stimulating UV radiation, the luminescence intensity is restored and the applied random code is destroyed.

The described method for verifying the authenticity of a banknote, including the application and reading of a random code due to exposure to a substance marked with stimulating radiation and analysis, the set of measured parameters, including the luminescence spectrum, the dependence of the intensity of the spectral bands on the exciting and stimulating radiation, can be implemented instrumentally, and thus can banknote authenticity to be established.

Claims (7)

1. The method of determining the authenticity of a multilayer product containing a carrier with a hidden protective marking deposited on its surface, the marking of which is made using a luminescent compound with a crystalline structure based on yttrium oxysulfide activated by ytterbium and cerium ions, or holmium and cerium ions, or ytterbium ions and holmium, namely, that the areas of the protective markings are exposed to constant exciting radiation in the spectral range of 930-970 nm, the level is fixed s sink luminescence, then produce a constant effect stimulating radiation in the spectral range of 330-370 nm and a fixed optical quenching of said luminescence at an invariance its spectral composition, relieve stimulating recovery after radiation and luminescence intensity establish the authenticity of the product. 2. The method according to p. 1, characterized in that they produce exposure to exciting radiation, sequentially change the wavelength of the stimulating radiation, fix the dependence of the intensity of the luminescent radiation on the wavelength of the stimulating radiation. 3. The method according to p. 1, characterized in that they produce exposure to exciting radiation, fix the level of luminescence, produce exposure to stimulating radiation, change the power of stimulating radiation, fix the dependence of the intensity of luminescent radiation on the intensity of stimulating radiation. 4. The method according to p. 1, characterized in that when detecting changes in the intensity of luminescence in areas of protective markings treated with stimulating radiation, a latent image and / or information is recorded. 5. A method for determining the authenticity of a multilayer product containing a carrier with a hidden protective marking deposited on its surface, the marking of which is made using a luminescent compound with a crystalline structure based on yttrium oxysulfide activated by ytterbium and cerium ions, or holmium and cerium ions, or ytterbium ions and holmium, namely, that the areas of the protective marking are exposed to pulsed or variable exciting radiation in the spectral range 930-970 nm, fi coding the intensity of luminescent radiation in the phase of acceleration or attenuation, produce exposure to pulsed or variable stimulating radiation in the spectral range 330-370 nm, fix the change in the intensity of luminescent radiation in the phase of acceleration or decay. 6. The method according to p. 5, characterized in that after exposure to exciting radiation, the temporal parameters of luminescence in the acceleration or decay phase are additionally fixed, and after exposure to stimulating radiation, a change in the temporal parameters of luminescence in the phase of acceleration or decay is recorded. 7. The method according to p. 5, characterized in that when detecting changes in the intensity of luminescence in areas of protective markings treated with stimulating radiation, a latent image and / or information is recorded.