JP5416764B2 - Machine-readable security elements and articles containing them - Google Patents

Description

  The present invention relates to machine-readable security elements and articles comprising them. Articles requiring machine-readable security elements include, for example, valuable documents (eg, paper and plastic supports such as banknotes, passports, visas, etc.), labels, tickets, and identification.

  In order to prevent counterfeiting and counterfeiting, people in the industry have attempted to manufacture articles with machine-readable security elements so that the articles to be protected are not altered or duplicated without detection by unauthorized persons.

The use of host lattices doped with rare earth ions is generally known in the art. These compounds absorb radiation at one frequency and emit radiation at a different frequency. Here, the radiation refers to UV, visible, near infrared, and infrared. When irradiated with radiation of a certain wavelength, these compounds emit at a second wavelength, and such emission is detected by a detector. Such luminescent compounds are called “luminophores” and can be ions or compounds.

A host lattice doped with a luminophore compound exhibits an emission profile that is generally characteristic of ions, but varies with the effects incorporated into the crystalline host lattice. Both absorbance and radiation can be measured with current laboratory equipment.

In order to make it more difficult for potential counterfeiters to decipher the security function, it is preferable to impersonate the spectrum created by the luminophore. Radiation can be camouflaged by using one or more rare earth metals and / or host lattices.

  WO 2006/024530 (A1) discloses the use of at least two luminescent materials that overlap the spectral emission band as a luminescent security functional system. Preferably, the luminescent materials have the same host lattice and different luminophores, or have the same luminophore and different host lattices. Here, the luminophore may be a rare earth metal.

WO 2005/035271 (A2) includes a machine readable coding system for security documents, including a first luminescent material and a second luminescent material, both of which emit light in a common emission region outside the visible spectral range. Is disclosed. Emission spectrum of the first luminescent substance and the second luminescent material, as the emission spectrum of the first luminescent material is characteristically supplemented by emission spectrum of the second luminescent material, at least a partial region of the known emission region Overlap. The luminescent material may be a host lattice doped with rare earth metals.

Emission spectrum of the luminophore can be disguised by using an absorbent material. The absorption spectrum of the absorbing material overlaps or covers the emission spectrum or the excitation spectrum of the luminophore and changes it in a specific way. These changes occur, for example, by “limiting” the spectral region or by “distorting” the excitation and / or emission spectra. In the simplest case, such a restriction is caused by separating the end regions of the spectrum, while such a deformation is caused by intentionally disappearing a narrow spectral range of a wide band spectrum or by certain spectral lines. It happens by removing.

U.S. Pat. No. 4,451,530 discloses changing the known emission spectrum and using characteristically modified parts for the authentication of security documents. Security elements are inorganic host lattices doped with luminophores such as rare earths, and dyes that change the emission spectrum of the luminophore by limiting the spectral region or by modifying the excitation and / or emission spectrum. It is made of one or more kinds of absorbent materials.

US Pat. No. 6,506,476 (B1) discloses the use of an inorganic host lattice doped with at least one rare earth metal containing thulium as an authentication feature for printed valuable documents. The authentication feature may be printed on the printed valuable document or may be added to the paper pulp. Doped host lattices generally absorb in the visible region of the spectrum, are excitable, and are transparent at least in the infrared spectral region. With high efficiency, the host lattice transfers the absorbed energy to thulium. The quantum yield of the luminescent material is preferably in the range of 50 to 90%. By absorption, the host lattice suppresses thulium radiation lines that occur in the visible region and possibly in the near infrared region.

U.S. Pat. No. 6,344,261 (B1) discloses a printed valuable document having at least one authentication feature that is a luminescent material based on a host lattice doped with at least one rare earth metal. The host lattice generally absorbs in the entire visible region of the spectrum and contains chromium as an absorbing material. This very broad band absorption by the host lattice obscures lines originating from doped rare earth metals in this region. At the same time, energy transfer occurs from the host lattice to the doped rare earth metal, thereby inducing radiation by the luminescent material. A very efficient stimulation of the rare earth metal occurs, leading to even greater radiation intensity.

US Pat. No. 6,479,133 (B1) discloses the use of an inorganic host lattice doped with two rare earth metals, thulium and holmium, as an authentication feature for printed valuable documents. The authentication feature may be embedded in the paper pulp or added to the printing ink. The host lattice contains a broadband absorbing component and transfers the absorbed energy to the rare earth doped metal with high efficiency. The quantum yield of the luminescent material is preferably in the range of 50 to 90%. The emission spectrum of rare earth metals is affected in a particular way by the absorbing components.

US Pat. No. 4,463,970 discloses the use of a camouflage material that can be a detection luminophore to prevent indirect detection of the pattern of excitable marking material by chemical laboratory analysis. Excitable marking substances are used to record information in codes. For example, the signal used for coding for concealment includes the emission spectrum of a camouflage material containing a luminophore. The camouflage substance may be any substance that exhibits wide-band radioactivity , such as an organic luminophore. The characteristic signal of the excitable marking material is only seen as a small clue added to the emission spectrum. Alternatively, one or more narrow-band luminophores may be added that emit at wavelengths other than the signal being measured, thus complicating the emission spectrum.

  In this technical field, it is generally known that two types of luminescent materials are used as authentication features for printed valuable documents. One luminescent material acts as an absorber and the other luminescent material acts as an emitter. Energy is efficiently transferred from the absorbent to the emitter.

  International Publication No. 2006/099642 (A1) discloses the use of two types of inorganic luminescent materials as security elements for security documents. The first luminescent material is excited by incident radiation. Energy is transferred between the first luminescent material and the second luminescent material, whereby the excitation frequency range of one luminescent material corresponds to the excitation frequency range of the other luminescent material.

  Japanese Patent Application Laid-Open No. 2002-212552 discloses thulium absorbed in the infrared range and the thulium energy level, efficiently transfers the absorbed light energy, and is an optional active element in the infrared range. An infrared emitting fluorescent material containing an inorganic material that is simultaneously activated by holmium emitting light is disclosed.

European Patent Application No. 1241242 (A2) discloses an anti-Stokes phosphor that is a luminophore for application to security documents, wherein the phosphor has an emission wavelength band that is greater than an absorption wavelength band. Also have a short wavelength. Anti-Stokes phosphors are host lattices doped with two types of rare earth ions. One of the dopants (eg yttrium) forms an absorber and the other dopant (eg thulium) forms an emitter. The intensity level between individual groups of radiation lines varies and depends on the concentration of absorber and / or emitter in the phosphor.

International Publication No. 2006 / 024530A1 International Publication No. 2005 / 035271A2 U.S. Pat. No. 4,451,530 US Pat. No. 6,506,476 B1 US Pat. No. 6,344,261 B1 US Pat. No. 6,479,133 B1 US Pat. No. 4,463,970 International Publication No. 2006/099642 A1 JP 2002-212552 A European Patent Application No. 1241242A2

In a first aspect of the invention, the present invention provides a machine readable security element comprising a mixture of at least two pigments. In the security element, a first pigment comprises a first inorganic host lattice having a first luminescent dopant ion that emits electromagnetic radiation at a first emission wavelength band, the second pigment has at least two kinds of dopants Including a second inorganic host lattice, wherein the first dopant of the second inorganic host lattice is the same as the first light-emitting dopant ion, and the second dopant is i) non-radiative energy transfer from the first dopant of the second inorganic host lattice. And ii) rare earth ions that emit electromagnetic radiation in a second emission wavelength band, where the second emission wavelength band has a negligible overlap with the first emission wavelength band. only it does not have a large part of the radiation from the first dopant of the second inorganic host lattice second dopant at one or more emission peaks It is removed by.

  In a second aspect of the invention, the invention provides an article comprising a support having a security element according to the first aspect of the invention. The article is a valuable article. The support is a paper or plastic product comprising a paper pulp or polymer material and a mixture of at least two pigments, the pigment being added to the pulp in papermaking or the polymer being extruded in addition to the security element in the paper or plastic product. The mixture is as defined in the first aspect of the present invention.

  In a third aspect of the invention, the invention provides a collection of articles according to the second aspect of the invention.

  In a fourth aspect of the present invention, the present invention provides an ink comprising a vehicle and a mixture of at least two pigments. When the ink is applied to the support to form a security element, the mixture is as defined in the first aspect of the invention.

  In a fifth aspect of the present invention, the present invention provides a printing method wherein a support is printed with ink according to the fourth aspect of the present invention.

In a sixth aspect of the invention, the invention provides a method for detecting the presence of a security element according to the first aspect of the invention. In the detection method, the element is irradiated with incident radiation at one or more wavelengths including a first dopant / first pigment absorption wavelength and a first dopant / second pigment absorption wavelength, and the radiation is passed through the detector. Use is detected in the first radiation band and the second radiation band.

It shows the absorption spectrum of the doped _Y 2 _{O 2} S in 1.0% (atomic%) Tm. The absorption spectrum is substantially identical to the absorption spectrum of Y ₂ O ₂ S doped with 1.0% (atomic%) Tm and 2.0% (atomic%) Ho. 1.0% (atomic%) emission spectrum of the doped _Y 2 _{O 2} S at Tm, and 1.0% (atomic%) Tm and 2.0% (atomic%) _Y doped with Ho 2 _{O 2} The radiation spectrum of S is shown.

In a first aspect of the invention, the invention provides a machine readable security element comprising a mixture of at least two pigments, wherein the first pigment emits electromagnetic radiation in a first emission wavelength band. The first pigment comprises a first inorganic host lattice having a first luminescent dopant ion that emits, and the second pigment comprises a second inorganic host lattice having at least two types of dopants, wherein the first dopant of the second inorganic host lattice is The same as the first light emitting dopant ion, the second dopant can be excited i) by non-radiative energy transfer from the first dopant of the second inorganic host lattice, and ii) emit the electromagnetic radiation into the second radiation. a rare earth ions emitting in the wavelength band, where the second emission wavelength band has only Gokuzu kana overlap of the first emission wavelength band, a second dough Cement erases most of the radiation from the first dopant of the second inorganic host lattice at one or more emission peaks.

“Erase most” means that the maximum intensity of the emission peak is substantially reduced and the emission peak is preferably less than 20% of the maximum intensity of the peak in the first pigment, more preferably the peak of the peak in the first pigment. Decreasing to less than 10% of the maximum intensity, most preferably less than 5% of the peak maximum intensity in the first pigment, means that the emission peak is eliminated so that it cannot be easily distinguished from the background noise of the spectrum. .

In one aspect, the first dopant absorbs electromagnetic radiation in the UV, visible or infrared spectral region at a first absorption wavelength, preferably UV in a first emission wavelength band at a wavelength higher than the first dopant absorption wavelength. Emits electromagnetic radiation in the visible or infrared spectral region.

  The first luminescent ion may be a transition metal such as chromium, vanadium, manganese, titanium, nickel, iron or cobalt. The first luminescent ions are preferably rare earth ions, more preferably lanthanides. Examples are given below.

Both the first radiation and the second radiation are in the IR region.

  Pigment host lattices include aluminate, bromide, chloride, fluoride, gallate, garnet (including all mixed garnets), germanate, molybdate, niobate, oxide, oxyfluoride, oxysulfide, sodium yttrium fluoride, silicate, sulfate , Sulfides, titanates, tungstates, and vanadates. The host lattice may be any known host inorganic lattice for rare earth cations, such as any of those disclosed in WO 2006/024530 A1.

  The host lattice for the first pigment and the second pigment may be the same or different. When the host lattices are different, in certain embodiments, the first dopant absorption is preferably in the same spectral region, and for the first pigment and the second pigment so that the same incident radiation source can be used for both pigments. It may be within a few nanometers.

  The incident radiation that excites the first dopant in the first pigment and the incident radiation that excites the first dopant in the second pigment may originate from different sources. This is because the two host lattices are substantially different, so that the absorption band of the first dopant is sufficiently different in the first pigment and the second pigment, so that narrow band excitation properly excites the main ions in both host lattices. This is necessary when using a narrow band excitation source when this is not possible. The first dopant can be excited at several wavelengths. In order to create a more compact and higher intensity excitation source, wavelength coupling is advantageous, for example two light sources are directed at the security element. An example of such a case is when there are multiple absorption peaks that provide the desired high transition state manifold.

The first radiation and second radiation band there is a difference of typically at least 50nm. The desired result is to have essentially a single excitation of both pigments, and the resulting spectral output of each of the different pigments may be that they may contain at least one emissive dopant in common and generally Separable. The radiation may be a narrow band or a wide band, or any combination, preferably at a wavelength of maximum intensity that is at least 50 nm apart.

Emission peak of the first dopant of the second pigment resulting from the same transition results in emission in the first emission band is largely erased by the second dopant.

The most efficient source of incident radiation is one in which light is more fully absorbed by the spectral absorption feature. Light radiation that can be part of an excitation source with non-overlapping absorption features should be avoided when high efficiency is required. The use of a relatively broad wavelength band source, such as an LED, may be selected because it is economically advantageous in that it is commercially available, robust to operation, and easy to maintain. Narrowband laser light sources are more efficient and are advantageous in that LEDs of suitable wavelengths are not available for some absorption spectra of suitable pigment combinations, but are expensive to operate and maintain. Those skilled in the art should select a suitable source that meets the system requirements. Excitation must be sufficient and the system function must meet all other performance criteria. These criteria include service life, environmental factors, eye safety and economic considerations.

The incident light has a narrow wavelength band and may be at least 50 nm shorter than the first emission band and the second emission band.

Incident light may have a very broad wavelength band, such as a light bulb or flash bulb. It is possible to pass the incident light through a filter to prevent the security element from being irradiated by light of the same wavelength as the first or second radiation, and then to detect by the detector. The incident source may be a narrower band than a general light bulb, but may be wider than a laser such as an LED.

  Incident radiation is preferably in the UV, visible and IR regions of the spectrum. The first and second pigment host lattices in the preferred embodiment are both substantially transparent in the visible region, ie, in the preferred embodiment, the host lattice is substantially colorless, but this is not a requirement. The advantage of the pigment being substantially colorless is that, for example, in a printing element, there is no substantial change in color when applied in large amounts to the support compared to the unadded state. If the pigment is not substantially colorless, in some embodiments it is used at a level that is low enough to avoid changes in the color of the support, or in other embodiments at a level where the color is visible.

The first and second dopants are M ²⁺ (eg Eu, Co, V and Dy), M ³⁺ (eg Cr, Ho, Pr and Nd), M ⁴⁺ (eg Cr) or M ⁵⁺ (eg Mn ions). ^Yes , preferably M ³⁺ , where M is a rare earth, preferably a lanthanide, or, for example, in the case of the first dopant, a transition metal, and the number + represents the valence state of the ion. The valence state affects the radiation properties of the element. The host lattice is selected to match the valence state of the element.

The first dopant in the first pigment and the second pigment may also emit electromagnetic radiation in one or more additional emission wavelength bands at wavelengths higher than the first dopant absorption wavelength. One or more such emissions are not substantially extinguished by the second dopant in the second pigment. It is useful for detecting such further radiation from the first dopant in both pigments.

In another aspect, the further emission wavelength is a wavelength higher than the first dopant absorption wavelength and the first emission wavelength, wherein in the second pigment, the second pigment is present in sufficient concentration in the second pigment. Most of the further radiation from can be eliminated. Erased radiation may correspond to a further radiation originating from the first dopant of the first pigment.

Detector is selected in consideration of the wavelength of the radiation to be detected, if necessary, the first radiation and the second (Naru and further) using a filter to separate the radiation. The detector has design parameters based on various requirements and conditions. They are selected for each individual system requirement by one skilled in the art based on, for example, spectral sensitivity, noise characteristics, impedance, cost, speed, effectiveness, and the like. Examples of the detector include a photomultiplier tube, Si, PbS, CdS, PbSe, InAs, InSb, Ge, HgCdTe, GaP, and InGaAs detectors.

Silicon detectors can detect photons up to 1100 nm, and silicon based detectors exhibit very low noise. This feature is advantageous when the phosphor emission levels are very low and require greater electronic amplification. Silicon detectors also have the advantage of being readily available and inexpensive.

InGaAs detectors can be used for higher wavelength detection. It has a lower signal to noise ratio, is generally more expensive and has fewer suppliers. Such detectors are useful for the present invention to detect radiation greater than 900 nm, and some detector models can detect up to 2600 nm. However, detector models with better sensitivity at higher wavelengths are much noisy and shunt resistance is reduced.

The first emission band and the second emission bands can be measured simultaneously, it is preferred that the each phosphor has a decay time constant of the similarity, this is not a necessary condition.

Those skilled in the art, selecting a first pigment and a suitable amount of the second pigment in the security element with respect to the detector used to detect a first radiation and second radiation would be possible. For example, silicon detectors exhibit very low NEP (noise equivalent power) because they can amplify the signal to a higher degree than, for example, InGaAs detectors with much higher noise characteristics. Those skilled in the art will recognize that the emission wavelength, emission intensity, emission focusing optics (if necessary), filter parameters, to obtain a satisfactory signal-to-noise ratio over all anticipated operating conditions of the security features and detection system. The amount of security features to be used will be determined based on detector type, response, area, environmental conditions and associated electronic amplification demands. It is desirable to make the security element more difficult for counterfeiters to decipher with the minimum amount of pigment and dopant in the security element. Those skilled in the art will evaluate dopants for detection systems that take into account the choice of host lattice, the ability to produce luminescent pigments, pigment size requirements, emission wavelengths, and intended use. (See PHOSPHOR HANDBOOK, Shigeo Shionogi, William M. Yen, CRD Press 1999, ISBN 0-8493-7560-6).

It may be desirable that the amount of the second dopant in the second pigment be sufficient to eliminate most of the one or more emission peaks due to the first dopant in the second pigment. The relative level of dopant can be selected by those skilled in the art according to available information regarding luminous efficiency and non-radiative energy transfer efficiency and / or empirically.

  In a second aspect of the invention, an article is provided that includes a support that holds a security element.

  The goods may be valuable documents (eg paper and plastic supports such as banknotes, passports, visas, etc.), labels, tickets and identification cards.

  The security element may be incorporated into the body of the support, in which case the support is preferably paper or plastic. Alternatively, the security element may be applied to a support, in which case the security element is preferably in the ink. One skilled in the art can select an appropriate particle size for each application. The mixture of pigments can be incorporated during the production of paper or plastic.

  U.S. Pat. No. 4,874,188 discloses that particles such as coarse particles, pellets or fibers are incorporated into paper pulp during paper making. These have coarse particles or pellets having a cross section of about 10 μm, and fiber lengths or pellet diameters of about several mm. The particle size used in the present invention is about 0.1 to 50 μm although it depends on the application.

The first pigment and the second pigment each have a particle size distribution, which is characterized by commercially available laboratory equipment such as Microtrac's laser diffraction particle size measurement system. The distribution is generally characterized by a D50 value where half of the volume is made of particles smaller than a certain diameter. Reference can also be made to the values of D90, D95 or D99. There are situations where the D50 and D90, D95 or D99 values change at far-away values. The particle size distribution is selected by their application method and final detection. When using particles, the requirements are set so that the luminous performance is within a certain tolerance. If the particle size is too large, the detected radiation standard deviation can be undesirably large. If the particle size is too small, the intensity of radiation from the two pigments is reduced and detection becomes more difficult.

  The article may have security elements applied in the layer or on the support, for example as a discontinuous layer, forming a predetermined pattern on the support. The mixture may be incorporated into fibers woven into a support to form a pattern, or may be incorporated randomly. A strip of polymer film containing the pigment may be incorporated into the article, for example, sandwiched between outer layers.

  The article may have a security element applied to the discontinuous layer by printing, which layer may contain another ink element.

  In a third aspect of the invention, a collection of articles according to the second aspect of the invention, wherein the security elements are the same in each article, for example a collection of various types of banknotes, all having the same security element. In addition, each security element can provide a collection of different articles with respect to a predetermined pattern on the support so that the printing pattern for each banknote type is different.

  In a fourth aspect of the invention, the ink comprises an excipient and a mixture, and when the ink is also applied to the support to form a security element, the mixture is as defined in the first aspect of the invention. It is.

  The ink can be used in lithographic, offset, intaglio, flexographic, gravure, ink jet, letterpress or screen printing processes. Each process has requirements set according to the type of printing process used. Larger particles clog certain print transfer surfaces, but are otherwise acceptable. Screen printing methods can accommodate fairly large particles.

  Suitable particle sizes for each printing method can be selected by those skilled in the art, as are suitable excipients and additives and formulation methods. In GB 2258660, the maximum diameter of particles suitable for use in a series of printing techniques is 40 μm or less, preferably 20 μm or less, most preferably less than 10 μm, for example 1-5 μm, even 1-2 μm. It is disclosed that there is. Such particle sizes can be used in the present invention.

  In a fifth aspect of the invention, the ink according to the fourth aspect of the invention is used to print on a support, preferably by a lithographic, offset, intaglio, flexographic, gravure, ink jet, letterpress or screen printing process. can do.

In a sixth aspect of the invention, a method for detecting the presence of a security element according to the first aspect of the invention is provided. In general, in the method, the element is irradiated with incident radiation at one or more wavelengths including a first dopant / first pigment absorption wavelength and a first dopant / second pigment absorption wavelength, and the radiation is obtained by using a detector. detected by the first emission band and a second radiation band.

In some embodiments, different detectors are used in the detection of the first radiation and second radiation, passes through the filter before reaching each detector by case radiation, filters one of the first radiation and second radiation Is selected such that the transmission of the other of the first radiation and the second radiation can be prevented. The detectors may be of the same type or different types.

The detector is selected according to individual job requirements. This is based on performance, environment, availability and economy. The present invention requires that each radiation to be detected has its own detection system that can include appropriate detectors and filters.

  A further embodiment of the sixth aspect of the present invention includes moving the security element to the detection position by a mechanical conveyor. This is done to ensure that the security element is correctly created during the manufacture of the article. This is also done at a later stage when the security element needs to be authenticated. The conveyor may or may not cause the security element to rest at the detection position. A conveyor is a member of a machine that contains a detector and makes machine readings of the security element used available. The detector can also be manufactured for static measurements such as those used in quality control. The design considerations for the various detectors can vary according to individual requirements.

  There are several known methods for producing appropriately sized pigment particles for use in printing and for incorporation into a support for printed valuable documents. A person skilled in the art can select an appropriate method for the two types of pigments used in the present invention. The method shown below is a method capable of producing a pigment. However, they do not limit the scope of the claims. Of course, other suitable methods may be used to produce the particles.

  German Patent Application Publication No. 10056462 (A1) discloses a method for producing a luminescent material. The method includes charging the ion exchange material with a rare earth metal cation and heat treating the charged ion exchange material. Examples of rare earth cations are mixtures of Yb and Er cations, or Nd and Cr cations or Yb and Y cations or Yb cations. Preferably, the charged ion exchange material is crushed to pigment size, preferably by grinding, before or after heat treatment. The ion exchange material is preferably a silicate, most preferably a zeolite. The heat treatment is performed at 1100 to 1200 ° C., preferably 1150 ° C. for 2 to 5 hours.

  EP 1386708 (A2) describes an ultrasonic aerosol generator, for example, a number of ultrasonic transducers installed under a liquid supply reservoir that forms aerosol droplets and energizing ultrasonically. An aerosol method and related apparatus for producing a powder product including use is disclosed. The carrier gas is delivered to different parts of the storage tank by a number of gas outlets that transport the gas from the gas delivery system. The aerosol is pyrolyzed to form particles, which are then cooled and collected. The powder product may comprise an inorganic host lattice doped with rare earth metal ions.

  WO 2006/078826 (A2) discloses a method of forming nanoparticles in a thermal spray system. The disclosed nanoparticles comprise an inorganic host lattice doped with rare earth metal ions. The method includes (a) applying a precursor medium comprising a liquid vehicle and a precursor to the element; and (b) spraying the precursor medium under conditions effective to form a population of nanoparticles. Wherein the formed nanoparticles comprise less than about 5% by volume of particles having a particle size greater than 1 μm.

  U.S. Pat. No. 6,344,261 (B1) discloses grinding and grinding an inorganic host lattice doped with rare earth ions to produce particles having an average particle size of less than 1 μm.

  The figure is described below.

FIG. 1 shows the absorption spectrum of Y ₂ O ₂ S doped with 1.0% (atomic%) Tm. This is substantially identical to the absorption spectrum of Y ₂ O ₂ S doped with 1.0% (atomic%) Tm and 2.0% (atomic%) Ho.

FIG. 2 shows the emission spectrum of Y ₂ O ₂ S doped with 1.0% (atomic%) Tm; and also doped with 1.0% (atomic%) Tm and 2.0% (atomic%) Ho. The emission spectrum of Y ₂ O ₂ S is shown.

The figure was prepared using a high resolution optical spectrometer. The curve in FIG. 1 was generated by monitoring the emission peak and scanning the desired excitation region (eg, 500-1000 nm). In FIG. 1, the excitation result was due to the designated emission peak in the wavelength region indicated by the scan. FIG. 2 was created by setting the excitation wavelength and scanning the specified emission spectral region monitored by the detector.

The following examples illustrate the invention. These examples do not limit the scope of the claims. The pigments in the examples were evaluated as a powder state on a non-optical brightener with a paper backing in a multi-grating spectrometer device configured with adjustable excitation and various radiation detections.

Example 1a
The first pigment was Y ₂ O ₂ S doped with 1.0% (atomic%) Tm. The first pigment containing the Tm dopant was manufactured using a general phosphor manufacturing method. The first pigment can be excited using, for example, 700 nm, 805 nm, or 910 nm light corresponding to the absorption peak shown in FIG. A suitable LED is Roithner-laser. com. Can be obtained from The emission spectrum is shown in FIG. Tm radiation centered at about 1800 nm was detected by an extended InGaAs detector equipped with a high resolution spectrometer. This radiation may correspond to the first radiation band in the present invention.

Example 1b
The second pigment was Y ₂ O ₂ S doped with 1.0% (atomic%) Tm and 2.0% (atomic%) Ho. The second pigment containing both Tm and Ho dopants was prepared using a general phosphor manufacturing method. The second pigment was excited using the same light source as in Example 1a. The absorption spectrum is substantially the same as in FIG. The Tm radiation that was present in Example 1a centered at about 1800 nm (FIG. 2, trace A) was substantially erased in the second pigment, as seen in trace B of FIG. Ho emits in bands with main peaks at 1975 nm and 2050 nm. Ho radiation in this spectral region can be detected using an extended InGaAs detector equipped with a high resolution spectrometer. This radiation may correspond to the second radiation band in the present invention.

Example 1c
The first pigment and the second pigment were produced separately. The first pigment was prepared as described in Example 1a and the second pigment was prepared as in Example 1b. The two pigments were then mixed in a 1: 1 ratio to produce a homogeneous mixture. This mixture was used as a machine readable security element. The first emission band and the second emission band was measured as described in Example 1a and 1b.

Example 1d
Printing inks can be produced by mixing the mixture described in Example 1c with a vehicle. When printing a support using this ink, when the ink is dried, the ink is illuminated by the light source of Example 1a. Detection system according to Example 1a and 1b identifies the first emission band and the second emission band of the present invention.

Claims (3)

A machine-readable security element comprising at least two mixtures of pigments, a first pigment comprises a first inorganic host lattice having a first luminescent dopant ion that emits electromagnetic radiation at a first emission wavelength band And the second pigment comprises a second inorganic host lattice having at least two types of dopants;
Here, the first dopant of the second inorganic host lattice is the same as the first light-emitting dopant ion, and the second dopant is excited by (i) non-radiative energy transfer from the first dopant of the second inorganic host lattice. And (ii) rare earth ions that emit electromagnetic radiation in a second emission wavelength band, and the second emission wavelength band has only a slight overlap with the first emission wavelength band. The machine readable security element, wherein the second dopant eliminates most of the radiation from the first dopant of the second inorganic host lattice at one or more emission peaks.   An ink comprising a vehicle and a mixture of at least two pigments, wherein when the ink is applied to a support to form a security element, the mixture is as defined in claim 1. The element is illuminated with incident radiation at one or more wavelengths including a first dopant / first pigment absorption wavelength and a first dopant / second pigment absorption wavelength, and the radiation uses a detector to emit a first radiation band and The method of detecting the presence of a security element according to claim 1 detected in a second radiation band.

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