RU216603U1 - SECURITY MARKING - Google Patents

Abstract

The utility model relates to the field of protecting valuable products from counterfeiting and is intended to determine the authenticity of protected products, such as technical devices (processors, displays, etc.), banknotes, securities, passports, pharmacological preparations, branded products (professional coffee machines, cars , gadgets, clothing, perfumery), museum exhibits, jewelry. The utility model is a security marking made on the basis of crystalline inorganic luminescent compounds of rare earth elements with Stokes luminescence in the spectral range of 1440-1600 nm in the form of a relief structure, erbium is used as a rare earth element, which is introduced into silicon with the formation of submicron-sized regions located on at least 2.5 µm apart. The utility model solves the problem of increasing the level of security of the product, providing the possibility of instrumental determination of the authenticity of the product based on the use of a complex sign of authenticity and expanding the range of marked products. 11 ill.

Description

The utility model relates to the field of protecting valuable products from counterfeiting and is intended to determine the authenticity of protected products, such as technical devices (processors, displays, etc.), banknotes, securities, passports, pharmacological preparations, branded products (professional coffee machines, cars , gadgets, clothing, perfumery), museum exhibits, jewelry.

Known security paper WO 1981003507 A1 (IPC C09D 5/22, B41M 3/14, D21H 21/48, B42D 15/00, publication date 06/27/2013, priority date 12/23/2011) with a security marking, which is a material based rare earth elements (REE) in a ferrite or garnet matrix. Identification of the protective marking is carried out by the intensity of the spectral bands of photoluminescence (PL) in the near IR range. The disadvantage of this protective marking is its insufficient reliability, since the PL spectrum is determined only by the configuration of the energy levels in REE atoms. This means that several materials with different chemical compositions can have identical PL spectra.

A valuable document with a security marking is known from the prior art (RU 2379195 C, IPC B42D 15/10, V41M 3/14, C09K 11/77, publication date 01/20/2010, priority date 11/25/2008). The marking contains at least one inorganic luminescent compound with a crystalline structure doped with REE ions. To determine the authenticity of the marking, measurements and subsequent analysis of the degree of dependence of the intensity of the Stokes and anti-Stokes luminescence bands on the power density of the exciting radiation are carried out. The disadvantages of this security marking are the need to use a variable power excitation source, as well as a limited range of valuable products to be protected, since the marking can only be applied by printing.

A security marking is known that matches the declared technical solution in the largest number of essential features and is taken as a prototype (RU 2614980 C1, IPC B42D 25/21, C09K 11/08, publication date 03/31/2017, priority date 12/21/2015). The marking is made using a luminescent inorganic compound based on REE, which has a luminescence of a given composition in the spectral range of 400-2500 nm under the influence of exciting radiation, which lies in the spectral range of 700-1000 nm, and additionally has the property of changing the luminescence intensity without changing its spectral composition when exposed to stimulating radiation in the spectral range of 300-700 nm. The disadvantage is the need for an additional pulse source of stimulating radiation in the spectral range of 300-700 nm to change the intensity of the luminescent radiation, which complicates the use of this protective marking. In addition, this solution has a limited range of valuable products to be protected, since the marking can only be applied by printing and does not allow protecting all types of products. Also, the level of protection of the marking is not reliable enough, since it is made on the basis of composite crystalline inorganic luminescent compounds of rare earth and alkaline earth elements and does not have sufficient resistance to external influences (mechanical, thermal, chemical), that is, it is temporary.

The objective and technical result of the proposed utility model is to increase the level of security of the product, to provide the possibility of instrumental determination of the authenticity of the product based on the use of a complex sign of authenticity and to expand the range of marked products. Complex security features are understood as technical solutions in which, during the instrumental control of authenticity, several parameters related in a given way are checked. An important requirement for security features for device authentication control is also their secrecy, that is, the impossibility of their identification in the visible range of the spectrum.

The essence of the utility model lies in the fact that the protective marking is made on the basis of crystalline inorganic luminescent compounds of rare earth elements with Stokes luminescence in the spectral range of 1440-1600 nm, while the marking is made in the form of a relief structure, erbium is used as a rare earth element, which is introduced into silicon with the formation of regions of submicron size located at a distance of not less than 2.5 microns from each other.

The technical result achieved in the implementation of this utility model is that a valuable product has on its surface or in its composition a carrier with a security marking containing a crystalline inorganic luminescent compound based on rare earth elements with Stokes luminescence in the spectral range of 1440-1600 nm, which is silicon doped with erbium (Er) ions. To achieve this technical result, it is proposed to use a complex security feature that occurs when creating an array of submicron-sized regions (holes) on the surface of a two-layer thin Er/Si film on a glass substrate. In the process of local laser irradiation, certain areas are doped with Er ions in accordance with a predetermined pattern and exhibit PL in the spectral range 1440-1600 nm (central wavelength 1530 nm) when excited by femtosecond laser pulses in the spectral range 510-540 nm, and the intensity and The shape of the luminescence spectrum of Er ions is determined by the parameters of laser action when Er ions are introduced into silicon. To increase the degree of protection, the security marking also includes an array of submicron-sized regions (holes) on the surface of the silicon film, which lack PL in the spectral range of 1440–1600 nm. Thus, the marking can only be read by scanning the carrier surface with simultaneous measurement of the PL spectra on a confocal spectrometer. At the same time, the complexity of the sign of authenticity lies in a certain reaction of the luminescent substance to the optical effect (the shape and intensity of the PL spectrum of each individual area), as well as the content of the protective marking as a whole, which is absent from publicly available materials known from the prior art, including in the technical solution taken as a prototype.

The proposed technical solution is based on the well-known physical phenomenon of the PL of Er ions distributed in silicon. Local femtosecond laser irradiation of a two-layer Er/Si thin film makes it possible to incorporate erbium into silicon in the affected area with high spatial precision while simultaneously crystallizing the silicon, thus creating a security mark. Then FL Er is used to read the security marking. In addition, the incorporation of erbium into the silicon matrix provides additional resistance to the security marking by limiting the possible environmental chemical attack on the luminescent regions and preventing the luminescent components from being easily detached from the carrier surface due to mechanical impact. The obtained areas of submicron size are located at a distance of not less than 2.5 microns from each other. Recording neighboring regions at a shorter distance leads to undesirable Er diffusion in silicon and, consequently, to the violation of the content of the security marking when it is read using PL signal mapping.

The essence of the utility model is illustrated in Fig. 1-11, where on:

fig. 1 shows its structure: 1 - glass substrate, 2 - silicon film, 3 - submicron-sized hole without luminescent properties, 4 - submicron-sized hole with luminescent properties;

fig. 2 shows the process of making a security marking embossed structure. Security marking is carried out on a carrier, which includes a glass substrate 1 and films of amorphous hydrogenated silicon 2 (100 nm thick) and erbium 5 (20 nm thick) located on its surface, in which, using laser radiation focused by a lens (objective) 6, an ordered array of submicron-sized regions with luminescent properties is created. Then, the erbium film is removed by chemical etching in hydrochloric acid, and non-luminescent regions (holes) located at a distance of at least 2.5 μm from each other are laser-etched under the same irradiation conditions next to the original marking, obtaining a relief structure 7 (Fig. .3);

fig. 3 is a top view of the relief structure of the security marking;

fig. 4 shows the characteristic size of one region (hole) determined using atomic force microscopy - 494±100 nm for cross section and 97±13 nm for depth;

fig. Figure 5 shows the experimentally obtained erbium PL intensity map at a wavelength of 1530 nm, where black crosses show the position of the recorded regions, white circles correspond to regions recorded later at different distances from the initial regions, and the dashed line corresponds to the boundary of the initial PL signal. The minimum distance between adjacent areas is 2.5 µm (when recording a security marking at a wavelength of 800 nm using an objective with a numerical aperture of NA=0.7). Writing neighboring regions at a distance of less than 2.5 µm leads to undesirable diffusion of Er in silicon and, consequently, to the violation of the content of the security marking when it is read using PL signal mapping;

fig. Figure 6 shows the PL spectra of the Er ion. It is known from the current technical level that the structure of the energy levels of the Er ion depends on its environment. Due to the Stark effect, the energy sublevels ₄ I ^15/2 and ₄ I ^13/2 of the Er ion are split, which can be detected in its PL spectrum as several individual peaks. If Er ions are surrounded by a crystalline phase, then its effect on each Er ion is equivalent. The spectral width of each peak can be quite narrow and determined by the uniform broadening and temperature of the material, so these peaks can be resolved spectrally. However, when Er ions are included in an amorphous (partially crystalline) matrix, each ion is affected differently by the disordered matrix. This leads to an additional inhomogeneous spectral broadening of each peak. Thus, the PL spectrum of Er in an amorphous matrix is a smooth PL curve with one peak at about 1530 nm, corresponding to the ₄ I ^15/2 → ₄ I ^13/2 radiative transition. The phase state of silicon, in which Er ions are located, is determined by the energy density of laser irradiation when writing a security marking;

fig. Figure 7 shows the measured dependence of the PL intensity on the energy density of laser irradiation when writing a security marking. It was also experimentally determined that the threshold for the formation of a crystalline phase is 1.0 mJ/cm ² , amorphous - 2.7 mJ/cm ² ;

fig. 8 shows the PL spectra of a separate area of the security marking after etching in hydrochloric acid for 10, 20 and 30 minutes, confirming the resistance of the luminescent area to the chemical attack of the environment;

fig. 9-10 show the process of reading a security mark;

fig. 11 shows the optical image of the security mark and the corresponding PL signal map.

Security marking works as follows. A carrier with a security marking is placed on the surface or as part of a valuable item. The user checks a complex security feature: the shape and intensity of the PL spectrum of each individual area (hole), as well as the content of the security marking as a whole (for example, a QR or alphanumeric code). In FIG. 9-10 shows the process of reading the security marking. When a carrier with a protective marking 7, consisting of a glass substrate 1 and an erbium-doped silicon film 2, is illuminated by femtosecond laser radiation 8, the wavelength of which is in the spectral range 510-540 nm, erbium ions are excited to a level of ₂ H ^11/2 and their subsequent relaxation corresponding to the radiative transition ₄ I ^15/2 → ₄ I ^13/2 in the spectral range 1440-1600 nm (central wavelength 1530 nm). In this case, luminescence is observed only for regions 4 containing erbium ions, and is absent in regions 3 where there are no erbium ions. The PL spectrum of a separate region is recorded by a spectrometer, and a piezo-shifter synchronized with the spectrometer is used to map the protective marking.

The proposed technical solution is illustrated by an example of a specific implementation.

A glass substrate 1 with a two-layer film consisting of silicon 2 and erbium 5, 100 nm and 20 nm thick, respectively, is proposed as a security marking carrier. Under point-by-point laser irradiation of film 2, silicon is doped with erbium with the simultaneous formation of holes 4 of submicron size on the surface of film 2 and a change in the phase state of silicon. Then the carrier is placed in a 10% HCl solution for 10 minutes to etch off the erbium 5 film, followed by cleaning with distilled water. After that, repeated point-by-point laser irradiation of the film 2 is performed to record holes of submicron size 3, which have no photoluminescence. The readout of the security marking was realized by point-by-point measurement of the photoluminescence spectra (mapping) when it was excited by femtosecond laser radiation at a wavelength of 525 nm. In FIG. 11 shows an optical image of the security mark (left) and the corresponding photoluminescence map (right).

Thus, the claimed utility model solves the problem of increasing the level of security of the product, providing the possibility of instrumental determination of the authenticity of the product based on the use of a complex sign of authenticity (the shape and intensity of the photoluminescence spectrum of each individual region, as well as the content of the security marking as a whole) and expanding the range of marked products (technical devices (processors, displays, etc.), banknotes, securities, passports, pharmaceuticals, branded products (professional coffee machines, cars, gadgets, clothes, perfumes), museum exhibits, jewelry and other luxury items).

Claims (1)

Protective marking made on the basis of crystalline inorganic luminescent compounds of rare earth elements with Stokes luminescence in the spectral range of 1440-1600 nm, characterized in that the marking is made in the form of a relief structure, erbium is used as a rare earth element, which is introduced into silicon with the formation of submicron size regions located at a distance of at least 2.5 microns from each other.

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