HK1181418A - Alkali metal and alkaline earth metal niobates and tantalates as materials for security features - Google Patents

Description

Alkali and alkaline earth metal niobates and tantalates as security marking substances

The invention relates to a security marking (security feature) having at least one luminescent substance for authenticating objects, such as security elements (security elements), security papers (security papers) or value documents (value documents), etc., to security elements, security papers and value documents provided with such a security marking, and to the use of the luminescent substance as a security marking substance for authenticating any kind of product.

A security marking or authentication feature is a marking instrument that protects a product, such as a value document or high value merchandise, from counterfeiting, or distinguishes any counterfeiting from the original. Generally, security markers have at least one marking substance, such as a luminescent, magnetic or electrically conductive substance, which may be visually and/or machine detectable. The marking substance or substances are arranged in some way, for example, randomly or in a geometric or patterned form or in a coded form. Such an arrangement forms a so-called security mark. The security marking used for the purposes of the present invention has at least one luminescent substance (luminescent substance) as marking substance.

It is understood that the security element is an object, such as a security thread (security thread), a label, mottling fibers (mottling fibers), a transfer element, etc., which has at least one security marking and is suitable for application to or incorporation into an object to be protected.

It is understood that a security paper is a paper which has been provided with at least one security marking or security element, but is not yet suitable for circulation, and is an intermediate product for the manufacture of a value document, it being understood that a value document is a product suitable for circulation.

Value documents such as bank notes (bank notes), checks, stocks, value stamps, identification cards, credit cards, passports and other documents, as well as packaging or other elements for product authentication.

The protection of value documents against forgery by means of luminescent materials has been known for some time. For example, EP0052624B2 discloses the use of luminescent substances based on host lattices (host lattices) doped with rare earth metals.

In DE102004034189A1, doping with rare earths and transition metals is described of the general formula XZO₄As a bankSecurity marking of a document, wherein X may be selected from a series of divalent or trivalent cations, and Z may in particular be niobium or tantalum.

It is also known to use luminescent substances with host lattices of alkali metal niobates and tantalates for applications in the laser, nonlinear optics, ferroelectric, piezoelectric fields. For these applications, single crystals pulled from the melt are generally used. However, crystals pulled from the melt do not have the ideal stoichiometric composition, but rather have lattice defects. In the case of lithium niobate, for example, the result of pulling (pull) from a homogeneous melt (concount melt) deviates slightly from LiNbO₃The Li content is 48.4 atomic% (based on Li + Nb). This results in an increased number of empty sites in the structure. It is also difficult to control dopant incorporation by pulling the crystal from the melt, and the dopant concentration in the melt and the dopant concentration in the single crystal sometimes differ greatly.

It is known from US6,330,939B1 to use LiNbO₃For specifically influencing the dielectric constant of the value document. Here, however, LiNbO₃Is undoped and thus does not emit light.

For luminescent security markings, substances are preferably used in which neither the absorption nor the emission is in the visible spectral region. The luminescent material is visible to the naked eye under suitable excitation if the emission wavelength is in the range of about 400nm to about 700 nm. This is desirable in certain applications, for example, authenticity checks by illumination with UV light. However, for most applications, emission outside the visible spectral region is advantageous, since the security marking can then be provided in a hidden form. When the detection is carried out, a special detector is needed.

However, the number of luminescent marking substances for security markings, i.e. luminescent substances with properties suitable for protecting value documents and in particular for automatic authenticity detection, is limited. Most inorganic and organic luminescent substances have unusual, broad spectra, defective emission intensities, or other disadvantages such as difficult manufacturing. Security markings using commercially available luminescent substances are not very recommendable.

Starting from this prior art, the invention is based on the object of increasing the amount of luminescent substances which are suitable for producing security or authentication marks, in particular for providing security elements, security papers and value documents with security marks which do not have the disadvantages of the prior art.

Within the scope of the present invention, the essential properties of the security marking luminescent substances provided for the present invention are in particular:

simple manufacture of a given, small particle size as required for incorporation into or application to a value document;

high emission intensity, even with small particle size, and the properties, i.e. easy identification, emission spectrum and/or absorption spectrum;

preferably in the near infrared region.

This object is achieved by a security marking as claimed in independent claim 1, by a security element, security paper and value document as claimed in independent claim 12, by the use of a luminescent substance, and as claimed in independent claim 15. The subject matter of the dependent claims is a development of the invention.

The security marking according to the invention has at least one luminescent substance of the general formulae I, II, III:

AXO₃:Z (I)

B_0.5XO₃:Z (II)

A_1-2yB_yXO₃:Z (III)

y is 0 to 0.5.

A represents an alkali metal, preferably lithium, sodium or potassium, particularly preferably lithium. The oxidation state of the alkali metal is + 1.

B represents an alkaline earth metal, preferably magnesium, calcium, strontium or barium. The oxidation state of the alkaline earth metal is + 2.

X represents niobium or tantalum. Niobium and tantalum have an oxidation state of + 5.

O represents oxygen in the valence state-2.

These elements form a host lattice in which the individual elements can be substituted for one another (for example, one element a is replaced by another element a) as far as the stoichiometry, size relationship and crystal structure permit.

The host lattice is doped with at least one element or cation that emits light upon appropriate excitation, a luminescence activator (Z).

The luminescence activator Z binds to lattice sites (lattice sites) or intercrystalline sites (intercrystalline sites) of the host lattice.

Z represents a rare earth metal (scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium), or some transition metal in a suitable oxidation state. The rare earth metals typically have an oxidation state of +3, but samarium, europium, thulium, and ytterbium may also have an oxidation state of +2, and cerium, praseodymium, terbium, and dysprosium may have an oxidation state of + 4.

The preferred rare earth metal ion is Nd³⁺、Dy³⁺、Ho³⁺、Er³⁺、Tm³⁺And Yb³⁺. Preferred transition metal cations are ions of the elements titanium, vanadium, chromium, manganese, e.g. Ti³⁺、V⁴⁺、Cr^2+/3+/4+/5+、Mn^3+/4+/5+/6+。

The structures of alkali metal niobates and tantalates and alkaline earth metal niobates and tantalates allow doping with a variety of cations Z, with the preferred luminescence activators being trivalent cations (e.g., rare earth metals and chromium). The doping amount is more than 0wt%, usually 0.05 to 5wt% of Z, preferably 0.1 to 2wt% of Z, based on the total weight of the luminescent material. Depending on the oxidation state and whether the cation Z is introduced into a lattice node or an interstitial site, some additional valence state will be created in the host lattice. Vacancies are created in the crystal lattice due to charge balance.

Due to the fact thatAs a commercial significance for applications in nonlinear optics or in band-pass filters for mobile phones for high-frequency circuits, etc., a large amount of scientific research in the field of alkali metal niobates is dedicated to matrix lithium niobate (matrix niobate). Thus, the different mechanisms and the influence of vacancies were studied in the most detail in this example. In LiNbO₃SE (SE = rare earth cation), the trivalent cation substitutes for lithium ions at the lithium lattice junction, thereby generating 2 additional charges. Two Nb are generated per 5 substituted lithium ions due to charge balance⁵⁺A vacancy.

Lattice defects such as vacancies tend to cause deterioration in emission properties, so that it is preferable to introduce additional element balancing charges in the host lattice to minimize lattice defects. By minimizing lattice defects, a substantial increase in luminous intensity can be achieved. Additional doping with titanium cations has proven particularly suitable. In the case of alkali niobates and alkali tantalates, the excess positive charge of the rare earth cation on the alkali sites (3+ instead of 1+) can be balanced, for example, by incorporating two titanium cations (4+) on the niobium/tantalum sites (5 +). Consequently, in this case, a particularly preferred doping ratio is two titanium cations per rare earth cation.

The additional elements introduced into the host lattice for charge balance or other reasons are not limited in any particular manner. It is important that the appropriate ionic size and ionic charge be of primary importance in order to be tolerated by the corresponding host lattice and to be able to stabilize therein.

The further elements are introduced not only for charge balancing but also, for example, for emission in a wavelength range in which the incorporated luminescence activator does not have the desired emission. It is then also possible to suppress undesired emissions in the relevant wavelength range by introducing ions which strongly absorb this range. In order to suppress undesirable visible light emission, for example, elements which absorb strongly in the visible wavelength range can be incorporated into the host lattice, for example transition metals such as Fe³⁺、Co²⁺、Ni²⁺. At the occurrence of those emissions, observedOr the detected wavelength range, the host lattice must of course be sufficiently optically transparent.

Another possibility is to change the excitation properties of the luminescent substance by introducing a sensitizer in the host lattice. Excitation of the activator can be achieved by energy transferred from the surrounding lattice ions (host lattice sensitized luminescence) or by other external ions (sensitizers) that absorb energy and transfer it to the luminescent activator. The formation of pairs of activator sensitizers results in a change of the excitation spectrum or in a higher luminescence intensity. Preferred sensitizers are rare earth cations and transition metal cations, particularly preferably chromium having a valence of + 3. For example, by introducing Cr into neodymium-doped lithium niobate³⁺The energy in exciting the chromium is obtained and transferred from the chromium to the neodymium.

If the absorbing component is also used as a cation for charge balancing, it is possible to partially replace the absorbing host lattice component by a non-absorbing component, such as aluminum, instead of introducing an additional absorbing component into the host lattice. By such a non-absorbing component part, the absorption of the luminescent substance, and thus the luminance, can be controlled. This may be desirable, for example, to use a luminescent substance that is not visible in the photoprinting ink (light printing ink), or to incorporate a luminescent substance into the light carrying material (light carrier material).

The location of doping agent incorporation is dependent on, in particular, the size of the cation to be introduced, the alkali/alkaline earth metal or niobium/tantalum location, respectively. In addition, factors such as the charge of the cation or the possible creation of an oxygen-coordinating polyhedron into which the site is introduced can influence this preference. In some cases, it is also possible to introduce at both of these locations.

In general, the incorporation behavior of the different matrices is similar, however, larger doping cations tend to enter sites for alkali or alkaline earth metals and smaller cations tend to assume sites for niobium or tantalum. Thus, for example, for lithium niobate, the ` A ` position (Li substitution) is preferably Ca²⁺、Mg²⁺、Zn²⁺、La³⁺It has been found that the 'B' position (niobium substitution) is preferably, for example: fe³⁺、Al³⁺、Sc³⁺、Cr³⁺、Zr⁴⁺、Ti⁴⁺、Sn⁴⁺、U⁶⁺、W⁶⁺. For substances having tetragonal tungsten bronze structure, e.g. potassium strontium niobate K_0.2Sr_0.4NbO₃Description of the introduction site (A')₂₍A")₄(C)₄(B')₂(B")₈O₃₀. Here the size of the introduced site is given as A'>A">The order of C decreases. Cations such as Li⁺、Na⁺、K⁺、Sr²⁺、Ba²⁺、Bi³⁺Or trivalent lanthanide ions are preferably introduced at the a site. Particular cations such as Li⁺Partial distribution can also occur at empty C sites. Cations such as Fe³⁺、Zr⁴⁺、Ti⁴⁺、W⁶⁺Preferably at the B site (Nb substitution).

In order to increase the chemical resistance of the phosphor, it is advantageous to apply the phosphor. The host lattices used according to the invention are generally quite stable with respect to external influences and are insoluble in water. However, they can be attacked by strong acids, which can adversely alter or even destroy their luminescent properties. Suitable coatings are, for example, protective layers of metal oxides, the metal component preferably being one of the group consisting of aluminum, barium, lead, boron, lanthanum, magnesium, silicon, titanium, zinc, zirconium, cobalt, copper, iron and mixtures thereof. Silica is particularly preferred. Suitable coatings and methods are as disclosed in WO 2006/072380.

As already mentioned, some individual embodiments of the phosphors used according to the invention are known in principle, but have not been considered for the validation field. They have hitherto been rendered unsuitable for this purpose. One of the reasons may be that the luminescent substances have hitherto been mainly studied in connection with laser applications and are therefore also produced in a manner suitable for laser applications. Laser applications require a single crystal, preferably as large a single crystal as possible, and the light-emitting substance is therefore produced by a method for obtaining such a single crystal, i.e. by pulling the single crystal from a homogeneous melt. However, such melts do not produce alkali metal niobates and tantalates with the exact stoichiometric ratio a: X =1:1, or alkaline earth metal niobates and tantalates with the exact stoichiometric ratio B: X =0.5: 1. The result is lattice defects. Furthermore, in the case of pulling a single crystal from a melt, it is generally not possible to obtain crystals having the same concentration of luminescence activator or other additives as the melt. In contrast, the concentration of the dopant in the melt differs greatly from the concentration of the dopant in the crystal. The resulting crystal is therefore subject to differences and gradients in dopant or additive concentration that must occur during synthesis by depletion or enrichment of dopants and additives in the melt. Such crystals are only suitable for the purpose of authenticating the marking to a very limited extent.

According to the invention, the phosphor is produced by annealing the thoroughly (annealing) mixed starting materials. For the manufacture of a catalyst having the general formula AXO₃The luminescent material Z is prepared by mixing oxides of the element XZ thoroughly, for example, by powder mixing together in a mortar, using an oxide or hydroxide or carbonate or peroxide of the element A, preferably a carbonate or hydroxide of the element A, for example, particularly preferably a carbonate of the element A, and then annealing at 900 to 1200 ℃, preferably 1150 ℃, for 1 to 20 hours, preferably 8 to 10 hours.

For the manufacture of a compound of the formula B_0.5XO₃Z, instead of the corresponding compound of element A, an oxide or hydroxide or carbonate or peroxide of element B, preferably a carbonate of element B, is used.

By appropriate weighing of the starting materials, the stoichiometry of the phosphor to be produced can be precisely predetermined. According to the present invention, it is desirable that the stoichiometric ratio is a: X =1:1 or B: X =0.5:1, and these stoichiometric ratios can be obtained without any problem. Also, the desired concentration of the luminescence activator Z can be reliably predetermined.

It is obvious that the above-mentioned stoichiometric ratio a: X =1:1 or B: X =0.5:1 represents the value that the host lattice itself has and is changed by doping the luminescence activator Z and, if applicable, further doping the substance. If the primary crystalThe lattice is doped with additional elements, such as activators Z, sensitizers, in order to suppress charge-balancing substances or quenchers which emit light in certain wavelength ranges, the stoichiometric ratio is changed in a desired manner by introducing an amount of the added elements, i.e. depending on the degree, certain lattice constituents are replaced by additional elements. If, for example, 5% of the alkali metal A is replaced by the element A 'while the other lattice components remain unchanged, the corresponding stoichiometric ratio results in A: A': X =0.95:0.05: 1. If in LiNbO₃Nd in the host lattice, neodymium replaces 5% of Li and Nb vacancies are created to maintain charge balance, resulting in a ratio of Li to Nd =0.95 to 0.98. If 1% of Li in the host lattice is substituted by Nd and charge balance is maintained by introducing Ti at the Nb sites, the resulting ratio is Li to Nb =0.99 to 0.98.

Such as LiNbO₃The crystal structure obtained by pulling from a homogeneous melt is significantly different from that obtained by the manufacturing method according to the invention on the other hand. In the case of lithium niobate, crystals of Li (Li: Nb =48.4:51.6) with a stoichiometric ratio of 48.4% were produced by pulling from a homogeneous melt. The vacancies thus generated have been studied extensively in the literature, for example, in Chinese Physics Letters, Vol.22, No.3(2005)588, Tang Li-Qin et al, "luminescence Enhancement in Mg-and Er-Codoped LiNbO₃Crystals ". Methods have been found to reduce vacancies, for example, by co-doping with magnesium. Co-doping with magnesium results in an increase in the luminescence intensity of the crystal pulled from the melt. For example, erbium doped LiNbO pulled from a homogeneous melt₃Co-doping of magnesium has been found to enable a significant increase in luminescence by reducing certain types of vacancies. However, in the crystals produced according to the invention, the situation is surprisingly the opposite. Magnesium co-doped LiNbO₃No improvement is produced but the light emission intensity is deteriorated. This is due to the fact that lithium niobate manufactured according to the present invention has an atomic ratio of a: X =1:1 and thus has a different defect structure than "isoconstituent" lithium niobate. Stoichiometric AXO produced without problems by annealing processes (recipe-free) compared to pulling from the melt₃And B_0.5XO₃Is more advanced, andthe process is simplified.

The annealing process according to the present invention does not produce separate, unagglomerated single crystals, much fewer large single crystals. This makes the luminescent substances according to the invention relatively unsuitable for applications in the fields of lasers, nonlinear optics, ferroelectrics, etc., but in no way hampers the use object according to the invention. On the contrary, if the luminescent substance is incorporated into security paper or value documents, it is advantageous for the grain size to be as small as possible, preferably in the range of 1 to 20 μm. If the luminophore is to be used as a component of a printing ink, the particle size should preferably be less than 6 microns, in particular less than 3 microns. Microcrystalline material from suitably sized aggregates of crystals is also readily available for use in the present invention. After annealing, the crystals or crystal aggregates can, where applicable, be ground to a suitable grain size in a suitable grinding mill, for example in a jet mill.

In the manufacturing method used in the present invention, it is particularly advantageous to be able to produce a powder material in the desired particle size range simply by selecting suitable annealing conditions. For this purpose, it is generally advantageous to select as high an annealing temperature as possible in order to obtain complete reaction of the educts (educts) and shorter annealing times. On the other hand, the annealing temperature must be chosen below the melting point of the target matrix to prevent the particles from sintering together. In some cases, it may be advantageous to further reduce the annealing temperature to prevent over-sintering of the particles or to limit grain growth in order to obtain suitably sized grains. Furthermore, advantageously, the annealing process allows for a simple and controlled incorporation of the luminescence activator and the further dopant, since the ratio of luminescence activator/dopant in the final product is determined exclusively by the ratio of the corresponding activator/dopant in the starting raw materials.

Hereinafter, some embodiments of manufacturing a luminescent substance according to the present invention will be explained.

Example 1

Nd (1mol%) doped Ca_0.5NbO₃

2.675 g CaCO₃7.234 g Nb₂O₅And 0.092 g Nd₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 2

Tm (1mol%) doped LiNbO₃

2.140 g Li₂CO₃7.747 g Nb₂O₅And 0.113 g Tm₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 3

Nd (1mol%) doped NaTaO₅

1.913 g Na₂CO₃8.025 g Ta₂O₅0.061 g of Nd₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 4

Nd (1mol%) and Ti (2mol%) doped NaTaO₃

1.927 g Na₂CO₃7.953 g Ta₂O₃0.062 g Nd₂O₃0.059 g TiO₂Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours. Compared with example 3, the product showed a luminous intensity about 5 times stronger due to charge balance by titanium.

Example 5

Yb (1mol%) doped NaTaO₃

1.911 g Na₂CO₃8.017 g Ta₂O₅0.072 g Yb₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 6

Yb (1mol%) and Ti (2mol%) doped NaTaO₃

1.925 g Na₂CO₃7.944 g Ta₂O₃0.072 g Yb₂O₃0.059 g TiO₂Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours. Compared with example 5, the product showed a luminous intensity about 8 times higher due to charge balance by titanium.

Example 7

Er (1mol%) doped LiTaO₃

1.415 g Li₂CO₃8.511 g Ta₂O₅And 0.074 g Er₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 8

Er (1mol%) doped Na_0.2Sr_0.4NbO₃

0.523 g Na₂CO₃2.840 g SrCO₃6.543 g Nb₂O₅And 0.094 g Er₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

Example 9

Nd (1mol%) doped K_0.2Sr_0.4NbO₃

0.672 g K₂CO₃2.799 g SrCO₃6.448 g Nb₂O₅And 0.082 g Nd₂O₃Mix well in an agate mortar. The mixture was annealed in a corundum crucible at 1150 ℃ for 10 hours.

The variation and combination of luminescent materials opens up numerous possibilities to influence the excitation and emission spectra of the luminescent materials and thus to produce a variety of security markings. In addition to evaluating the excitation and/or emission spectra, it is also possible to use the lifetime or decay time of the luminescence for differentiation in the test method. With regard to the evaluation, it is also possible to consider, in addition to the wavelengths of the excitation or emission lines, their number and/or shape and/or their intensity, so that any coding can be represented. Furthermore, the luminescent substance may be combined with one or more other marker substances, such as magnetic or conductive marker substances, to constitute a security marker.

The security marking according to the invention is formed on or in a carrier material, so that a security element, security paper or value document is produced depending on the type of carrier material.

For example, in the case of the production of security papers or documents of value on the basis of paper or plastic, the luminescent substance can be mixed into the paper stock or plastic stock (plastic mass) during the production thereof, so that a security marking is formed in the body of the security paper or document of value.

Alternatively, the luminescent substance may be added to the printing ink or coating composition and printed or applied in another way on the whole area (full area) or partial areas of the value document or security paper, for example in the form of letters or patterns. The security marking thus produced can be formed, for example, as a geometric or pattern drawing, writing or coding.

As an alternative to being applied to, or incorporated into, the carrier material in the form of security paper or value documents, the security symbol according to the invention can also be formed on or in a separate carrier material made of paper or plastic. For this purpose, the luminophore is mixed into the paper stock or the plastic web at the time of production of the separate carrier material, or into the coating composition, or into the printing ink, which is then applied or printed onto the surface of the separate carrier material, as described above, as carrier material for security papers and documents of value. The carrier material provided with the security symbol in this way can be used as a security element and be embedded wholly or partly in the security paper or value document or fastened to the surface of the security paper or value document. The security element according to the invention may be, for example, a security thread, mottled fiber, a label or a transfer element (transfer element).

The security marking, security element, security paper or value document having at least one luminescent substance is excited for checking authenticity, the light used having a suitable wavelength in the range from 400 to 1600nm, particularly preferably in the range from 500 to 1000 nm. Thus, at least one property of the light emitted (confined) as a result of excitation of the at least one luminescent substance (e.g. band intensity, band position, decay time) is obtained and, compared to the known property of the at least one luminescent substance (e.g. in example 7, emission of Er bands at 983 and 1543 nm), authenticity can be confirmed if the obtained and expected properties sufficiently match, i.e. within a preset, tolerable deviation range.

Hereinafter, the present invention will be described with reference to the accompanying drawings. The scale shown in the figures does not correspond to the scale that exists in reality and is primarily intended to improve clarity.

Figure 1 is a cross-section of a value document according to the invention.

Fig. 1 shows an embodiment of a value document according to the invention in the form of a bank note 7. The bank note 7 has a paper carrier material 1 to which the security element 2 according to the invention is affixed. The security element 2 is a sticker (packer) with a paper or plastic layer 3, a transparent cover layer 4 and an adhesive layer 5. The sticker 2 is attached to the value document base 1 by means of an adhesive layer 5. Luminescent substances 6 are contained in the layer 3, the luminescent substances 6 being randomly arranged, forming the security marking according to the invention of the sticker 2.

In addition, the luminescent substance may also be contained in a printing ink (not shown) which is printed on one of the sticker layers, preferably on the surface of layer 3.

Claims (15)

1. A security marking having at least one luminescent substance for authenticating a security element, security paper, value document or another object, which at least one luminescent substance has a host lattice doped with at least one luminescence activator, wherein the at least one luminescent substance has the general formula:

AXO₃:Z (I)

B_0.5XO₃:Z (II)

A_1-2yB_yXO₃:Z (III)

wherein

A is at least one element from the group consisting of alkali metals, preferably Li, Na and K,

b is at least one element from the group consisting of alkaline earth metals, preferably Mg, Ca, Sr and Ba,

x is Nb and/or Ta,

z is a luminescence activator and is at least one element from the group consisting of rare earth metals and transition metals in an oxidized state, wherein the relevant transition metal is activatable to luminesce, and

0<y<0.5，

and wherein optionally the host lattice is additionally doped with one or several elements E

As a luminescent sensitizer, and/or

For suppressing certain emission wavelengths, and/or

-for charge balancing.

2. The security symbol according to claim 1, wherein the luminescent substance has the general formula:

AXO₃:Z

wherein

A represents Li, Na or K,

x represents Nb or Ta, and

z represents a rare earth metal in oxidation state +3 or represents Ti³⁺Or V⁴⁺Or Cr²⁺Or Cr³⁺Or Cr⁴⁺Or Cr⁵⁺Or Mn³⁺Or Mn⁴⁺Or Mn⁵⁺Or Mn⁶⁺。

3. The security symbol according to claim 1, wherein the luminescent substance has the general formula:

B_0.5XO₃:Z

wherein

B represents Mg, Ca, Sr or Ba,

x represents Nb or Ta, and

z represents a rare earth metal in oxidation state +3 or represents Ti³⁺Or V⁴⁺Or Cr²⁺Or Cr³⁺Or Cr⁴⁺Or Cr⁵⁺Or Mn³⁺Or Mn⁴⁺Or Mn⁵⁺Or Mn⁶⁺。

4. The security marking according to any one of claims 1 to 3, wherein the luminescent sensitizer is selected from the group of rare earth cations or transition metal cations and is preferably chromium in oxidation state + 3.

5. The security marking according to any one of claims 1 to 4, wherein the element for suppressing certain emission wavelengths is selected from the group of transition metal cations, preferably coloured transition metal cations, and particularly preferably iron in the oxidation state + 3.

6. The security symbol according to any one of claims 1 to 5, wherein the element for charge balancing is selected from the group of transition metal cations or rare earth cations or cations of third and fourth main group elements, and preferably titanium in oxidation state +4 or aluminium in oxidation state + 3.

7. The security symbol according to any one of claims 1 to 6, wherein the luminescent substance is present in powder form with a particle size in the range from 1 μm to 20 μm, preferably <6 μm, particularly preferably <3 μm.

8. The security symbol according to any one of claims 1 to 7, wherein the luminescent substance is obtained by a method having the following steps:

-intimately mixing an oxide or hydroxide or carbonate or peroxide of element A and an oxide or carbonate of element X and an oxide or carbonate of element Z in such a ratio in number that the atomic ratio A: X: Z corresponds to the luminescent substance AXO₃Z, wherein for the assumed ratio Z =0, the desired atomic ratio is a: X =1:1,

annealing the mixture at a temperature of 900 to 1200 ℃, preferably 1150 ℃, for a time of 1 to 20 hours, preferably 8 to 10 hours,

optionally grinding the product to the desired particle size, and

-optional use of a protective coating, preferably SiO₂A coating coats the luminescent substance particles.

9. The security symbol according to any one of claims 1 to 7, wherein the luminescent substance is obtained by a method having the following steps:

-thoroughly mixing the oxide or hydroxide or carbonate or peroxide of the element B and the oxide or carbonate of the element X and the oxide or carbonate of the element Z in such quantitative ratios that the atomic ratio B: X: Z corresponds to the luminescent substance B_0.5XO₃Z, wherein for the assumed ratio Z =0, the desired atomic ratio is B: X =0.5:1,

annealing the mixture at a temperature of 900 to 1200 ℃, preferably 1150 ℃, for a time of 1 to 20 hours, preferably 8 to 10 hours,

optionally grinding the product to the desired particle size, and

-optional use of a protective coating, preferably SiO₂A coating coats the luminescent substance particles.

10. Security marking according to claim 8 or 9, wherein a further oxide of at least the element E is added, mixed and annealed sufficiently to form the host lattice AXO₃Or B_0.5XO₃In which, when element E is incorporated in the host lattice in place of one of the elements a, B or X, the quantitative ratios are selected such that the following atomic ratios are present in the doped phosphor:

(A + E): X =1:1, or

A (X + E) =1:1, or

(B + E) X =0.5:1, or

B:(X+E)=0.5:1。

11. A security element, security paper or value document, which is provided with a security marking according to any one of claims 1 to 10.

12. A security element, security paper or document of value according to claim 11, wherein the luminescent substance is incorporated into the security element, security paper or document of value.

13. Security element, security paper or document of value according to claim 11, wherein the luminescent substance is applied or printed by means of a coating composition or by means of a printing ink over the entire area or certain regions on the surface of the security element or security paper or document of value.

14. Use of a security marking having at least one luminescent substance as a marking substance for authentication, wherein the security marking is defined by any one of claims 1 to 10.

15. A method for checking the authenticity of a security marking according to one of claims 1 to 10 or a security element, security paper or value document according to one of claims 11 to 13, wherein the at least one luminescent substance is excited, a property of the light emitted by the at least one luminescent substance as a result of the excitation is captured, the obtained property is compared with a known property of the at least one luminescent substance, and the authenticity is determined if there is a sufficient match.