Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
  • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
  • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
  • G06K7/12—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using a selected wavelength, e.g. to sense red marks and ignore blue marks
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7767—Chalcogenides
  • C09K11/7769—Oxides
  • C09K11/7771—Oxysulfides
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7767—Chalcogenides
  • C09K11/7769—Oxides
  • C09K11/777—Oxyhalogenides
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7772—Halogenides
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
  • G07D7/12—Visible light, infrared or ultraviolet radiation
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
  • G07D7/12—Visible light, infrared or ultraviolet radiation
  • G07D7/1205—Testing spectral properties

Definitions

• the present invention relates to an advanced product security system and to an advanced method for authentication of a security article according to the preambles of the independent claims.
• Coating composition containing up-converting materials, particularly incorporated as pigments in coating compositions are well known and have been described for applications in document security in several publications, e.g. GB 2 258 659, GB 2 258 660, M. Martindill in Paint Polymers Color Journal, 8, 1996.
• Luminescent materials can absorb certain types of energy acting upon them and subsequently emit this absorbed energy as electromagnetic radiation. Down-converting luminescent materials absorb electromagnetic radiation at a higher frequency (shorter wavelength) and re-emit it at a lower frequency (longer wavelength). Up-converting luminescent materials absorb electromagnetic radiation at a lower frequency and re-emit part of it at a higher frequency. Luminescent materials are used for coding and marking of mass-produced goods, high value branded articles and security documents. In certain cases an up-converting luminescent is added as a hidden "taggant" to a transparent or colored coating composition or printing ink, which is applied to branded goods in form of barcodes, company emblems, labels, etc. This allows a subsequent recognition of the genuine article in the fight against counterfeiters and product piracy.
• Light emission of luminescent materials arises from excited states in atoms or molecules.
• the radiative decay of the excited states has a characteristic decay time which depend on the material and can range from a lifetime of shorter then 10 "9 s to several hours. This means that between excitation and light emission there is a certain time span.
• Most of the luminescent materials or up- converters, particularly up-converting materials are suitable for creating machine readable codes.
• Machine readability is a prerequisite for the application of up-converters in mass-produced goods since it is widely used in the automation, automatic sorting processes, in control of production batches, authentication of goods, quality and packaging. Machine readability is of course also used in security applications for the purposes of counterfeit and fraud detection, the so called "machine verification”.
• Up-converting materials are of inorganic nature and consist essentially of a crystal lattice in which rare-earth ions are present as activators and sensitizers.
• the excitation and emission characteristics of up-converting materials are inherent characteristics of the rare earths employed. Their corresponding optical absorption and emission processes are due to electron transitions within the incompletely filled 4f shell of the rare earth ion. This electron shell is strongly shielded from the chemical environment of the atom, such that variations in the crystal lattice, thermal vibrations, etc. have only a marginal influence on it. Consequently, rare-earth ions have narrow band optical absorption and emission spectra, which are to a great extent independent of the nature of the crystal lattice. The sharp, discrete bands and the low interaction with the crystal lattice usually result in a high saturation of the luminescence color and a high luminescence quantum yield.
• Rare-earth ion luminescence activators have relatively long-lived excited states and a particular electronic structure. This permits the energy of two or more photons in succession to be transmitted to one single luminescence centre and cumulated there. An electron is thus promoted to a higher energy level than that corresponding to the incoming photon energy. When this electron returns from its higher level to the ground state, a photon having about the sum of the energies of the cumulated exciting photons is emitted. In this way it is possible to convert e.g. IR radiation into visible light.
• Alkali and alkaline earth metal halides and the halides, oxyhalides and oxysulfides of yttrium and lanthanum and gadolinium are principally used as the host material, while e.g. Er 3+ , Ho 3+ and Tm 3+ serve as activators. Additionally ytterbium (3 + ) and/or other ions can be present in the crystal lattice as sensitizer to increase the quantum yield.
• Up-converting materials which are stable enough for being incorporated in carrier media have been extensively described in literature in view of quality and quantity of host lattices, manufacturing processes, rare earth activators, excitation and detection modes. Counterfeiters may therefore have access to up-converting materials and the published technology and eventually can imitate security markings; thus product security aspects are not longer provided.
• the product security systems as described in GB 2 258 659 and GB 2 258 660 comprise security markings based on up-converting materials which depend on absorption of two or more photons of a same wavelength. This requires active ions which have energy levels at almost regular intervals, i.e. where at least the distance between the ground and first excited state of the rare earth ion is substantial equal to the energy distance between the first and the second excited state. This requirement is approximately fulfilled only in Er + , Ho 3+ and Tm 3+ and represents thus a major limitation to the extension of the available up-converter product palette.
• composition and manufacturing process of new and uncommon up-converting materials shall be provided.
• an advanced product security system comprising at least one up- converting material which comprises at least one activator ion having discrete energy levels as at least part of a security marking and at least one authenticating equipment.
• the equipment comprises at least one source of electromagnetic radiation of at least one first preselected wavelength and at least one second source of electromagnetic radiation of at least one second preselected wavelength said first and said second wavelength being different from each other and being chosen such as to cause the up-converting material to release electromagnetic radiation upon combined irradiation with at least said first and second wavelength.
• Said released electromagnetic radiation comprises radiation of at least one further third wavelength which is specific for the return of at least one electron from an energy level at said activator ion to which the electron is excited by the combined radiation of at least said first and said second wavelength.
• the further third wavelength is different from said first and said second wavelength.
• product security system stands for the combination of a compound containing inherent properties and a corresponding authenticating equipment or reading/detecting device which is able to measure and/or analyze and/or quantify said inherent properties by an optical, electronic and/or mechanical device.
• security article is to be understood as the article comprising said up-converting material with at least one activator ion having discrete energy levels as a security marking and which releases radiation upon combined excitation with radiation of at least two wavelengths different from each other.
• the security marking can be incorporated in a coating composition, in particular in form of a printing ink, and applied as a layer to the security article.
• the security marking is incorporated in the material constituting the security article, e.g. in the paper forming the bank note.
• the security marking can also be applied or/and incorporated in other security marking such as hologramms.
• the advanced system of the present invention enlarges the capacity of product security.
• the application of up-converting materials for security marking is not longer limited to those materials which have energy levels at almost regular equal-spaced intervals but enable according to the invention any arbitrary rare-earth activator in to be used, as long as it has sufficiently long-lived intermediate excited state and a host matrix stable to the environment of application.
• the group of rare earth ions as activators are considerably expanded.
• the authentication equipment comprises two or more sources of electromagnetic radiation, wherein the first source emits radiation of the first preselected wavelength and the second source emits radiation of the second preselected wavelength. Further sources can emit radiation of further wavelengths.
• the sources can be combined in the same physical device.
• the source/sources of electromagnetic radiation is/are laser/lasers or comprise lasers.
• Simultaneous irradiation with a source of said second wavelength, corresponding to said second energy gap, can rise the ion population in said first excited state further up to said second, higher excited state.
• the resulting population of ions in said second excited state is roughly proportional to the product of the irradiation intensities of both, said first and said second light source.
• the electron is promoted from the ground to the first excited state by radiation of the first preselected wavelength and it is further promoted from the first excited state to the second excited state by radiation of the second preselected wavelength.
• the electron is promoted to even higher excited states by further exposing the up-converter to radiation of adapted wavelengths.
• the electron is promoted from the ground state to the first excited state, by radiation of the first preselected wavelength, subsequently it falls back to an "intermediate" state less in energy than the first excited state but not identical in energy to the ground state and is promoted thereafter from that "intermediate" state to the second excited state by a second preselected wavelength.
• the excitation to the second or higher excited states can thus be regarded as a cooperative excitation from at least two spectrally defined light sources.
• the authenticating equipment is portable or stationary.
• the laser or lasers can emit radiation of the preselected wavelengths in a continuous mode.
• the laser emits radiation in a pulsed mode with pulses having a peak power sufficient to induce a detectable emission of said up-converting material.
• the laser has a peak power equal or more than 1 W and even more preferably of about 10 W.
• the pulse repetition frequency and the width of the laser pulses are selected in a way that the mean power of the laser is sufficiently small so as not to produce eye hazard.
• the laser mean power is equal or less than 5 mW and more preferably equal or less than 1 mW and even more preferably equal or less than 0.5 mW.
• the pulse duration of the laser pulses is equal or less than 10 ⁇ s, preferably equal or less than 1 ⁇ s, and even more preferably equal or less than 100 ns.
• the pulse repetition frequency is equal or less than 10 kHz preferably equal or less than 1 kHz and even more preferably equal or less than 100 Hz.
• all lasers are processed in pulsed mode and in that comply with the limitations given before.
• Preferably all lasers are laser class 1 compatible.
• the authenticating equipment further comprises optical elements for directing and/or focusing the laser beam onto the up-converting material or for producing a parallel beam of light. In addition it can comprise optoelectronic detecting devices.
• the authenticating equipment can be coupled to a computer or microcontroller chip which evaluates and processes the emission data.
• the irradiation with at least the first and second preselected wavelength may occur exactly at the same time or can be delayed in time with respect to each other. Delay time must be chosen within the range of the lifetimes of the corresponding exited states.
• electromagnetic radiation encompasses radiation (for both excitation and emission) of wavelengths in the range of 1 NM to 1 mm.
• most of the excitation radiation and most of the emitted radiation is radiation with wavelengths in the range of 100 nm to 10 ⁇ m thus encompassing invisible UV - and IR - electromagnetic radiation.
• the further emitted radiation of the specific predetermined third wavelength which serves for detection is in a range of between 150 nm to 2500 nm .
• the further emitted radiation of the specific predetermined third wavelength which serves for detection is visible to the naked human eye and is in range of between 400 nm to 600 nm.
• the predetermined third wavelength is detectable by a silicon detector.
• the specific third wavelength which serves for detection is invisible to the naked human eye and is comprised preferably in the range of between 180 nm to 400 nm.
• the emitted radiation of the specific wavelength which serves for detection of the up-converting material is invisible to the naked human eye and is comprised preferably in the range of between 700 nm to 2'500 nm, preferably in the range of between I'lOO nm and 2'500 nm.
• the radiation of the specific third wavelength is machine detectable and readable.
• the sensitivity of the eye is about 1 lm/m2 for the color receptors, and 0.01 lm/m 2 for the white light receptors.
• Detectable means in this context that the emission can be detected with the help of an appropriate optoelectronic detecting device.
• Optoelectronic detection is possible down to the level of single-photon counting, that means about 10 -14 lm/m 2 .
• the up-converting material needs not to be excited with a continuous ray of said first and said second preselected wavelengths. A response can already be detected to single excitation pulses of both wavelengths.
• Up-converting materials with rare-earth activator ions having approximately regularly spaced energy intervals between ground state and the first few excited states are already well known for security applications.
• the present invention emphasizes the use of rare-earth activator ions having irregularly spaced energy intervals between their different states for up- converting phosphors of another kind, which are useful for security applications.
• the up-converting material can be a crystalline component selected from the group consisting of pure or mixed alkali and alkaline-earth lanthanide halides and pure or mixed oxyhalides and oxysulfides of yttrium and lanthanum or gadolinium as host matrix having incorporated rare earth ions as activators and optionally as sensitizers.
• the up-converting material is a pigment with a particle size in the range of between 0.1 ⁇ m to 50 ⁇ m more preferably in the range of between 1 ⁇ m to 20 ⁇ m and even more preferably of between 3 ⁇ m to 10 ⁇ m.
• the pigment which is applied in a product security system comprises glass ceramic particles.
• Glass ceramics are composite solids, which are formed by controlled devitrification of glasses. They can be manufactured by heating a suitable precursor glasses to allow for partial crystallization of part of the glass composition. Glass ceramics comprise thus a certain amount of a crystalline phase in an embedded glass phase.
• the glass ceramics crystalline phase is a luminescent material.
• a luminescent material which are not stable in an ordinary environment, and which can in this way be protected from the adverse influence of oxygen, humidity, etc.
• the glass matrix protects the crystals from dissolution in an adverse environment, and permits incorporation into a coating composition or the like. New types of luminescent materials are thus amenable to printing applications by this method.
• luminescent host materials are e.g. water soluble to a certain or a large extent, like the fluorides, chlorides or bromides of the lanthanide elements.
• the solubility is due to the rather weak electrostatic crystal lattice forces tied to mono-negative anions.
• the same materials show, due to the same reason and/or to the presence of heavy ions, only low-frequency vibrational modes (phonon modes) of their crystal lattices. That the absence of high-frequency vibrational modes results in largely increased excited state life times and luminescence quantum yields.
• the crystalline component of the glass ceramics has a phonon energy not exceeding 580 cm “1 , preferably not exceeding 400 cm “1 and even more preferably not exceeding 350 cm “1 .
• phonon energy not exceeding 580 cm “1 , preferably not exceeding 400 cm “1 and even more preferably not exceeding 350 cm “1 .
• These values stand for rather low-phonon energy solids, which are especially suitable as luminescence hosts because they allow for emissions from excited energy levels that would otherwise be quenched in high phonon energy solids, such as oxides or the like.
• Phonons are crystal lattice vibrations in a material.
• the ! G level of Pr 3 * is only 3000 cm “1 above the 3 F 4 level.
• an oxide matrix such as a praseodymium glass
• Si-O vibration phonons (1100 cm “1 ) are required to bridge this gap.
• any excited electron in the *G 4 level will rapidly return to the 3 F level by exciting crystal lattice phonons, and no electromagnetic radiation of the corresponding wavelength is produced.
• the phonon energy is 350 cm "1 , and the *G to 3 F transition of the Pr 3+ ion occurs radiatively. Additionally, the live time of the ! G state is strongly increased.
• the heavy metal fluoride glasses such as e.g. ZBLAN (53ZrF 4 -20BaF 2 -4LaF 3 -3AlF 3 -20NaF) have half the maximum phonon energy of silicates and thus take twice as many phonons to quench the G 4 level of Pr 3+ .
• ZBLAN glasses a well known host lattice for laser and fibre-optic applications, can also be used as the glass component of glass ceramic composites according to the present invention.
• the glass ceramic is substantially transparent to electromagnetic radiation in the range of between 400 nm to 750 nm, i.e. in the visible range of the electromagnetic spectrum.
• Transparency of glass ceramics is determined by the average dimensions of the embedded crystals and/or the refractive index difference between the crystals and the glass matrix.
• the average dimension of crystals is not exceeding 40 nm.
• the average distance from one crystal to another crystal being embedded in the glass matrix may not exceed 50 nm, preferably not exceeding 40 nm.
• the protection of the crystals by the glass matrix Apart from transparency another aspect being related with the dimension limitations of the crystals is the protection of the crystals by the glass matrix. Those host crystals up-converting properties having poor stability towards environmental influences and being neither physically or chemically resistant towards organic resins, solvents, humidity, etc. can effectively be protected by a glass-matrix having such chemical and physical resistance. Even grinding the glass ceramics to the desired particle size does surprisingly not adversely affect the up-converting properties of the glass ceramics. The crystals remain sufficiently protected by the glass matrix when the crystal is sufficiently small.
• At least one crystal embedded in the glass matrix comprises an active ion.
• the active and/or sensitizer ions being present in at least one of the crystals in the glass matrix are rare earth ions having an appropriate electronic structure, particularly suitable are rare earth ions selected from the group consisting of Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Tb 3+ , Dy 3 *, Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ .
• the glass ceramics is an oxyfluoride glass ceramics. Oxyfluorides have the low phonon energy of a fluoride matrix and the durability and mechanical properties of an oxide glass. The oxide glass will determine the mechanical and physical properties of the composite whereas the optical properties of the active ion will be controlled by the embedded fluoride crystalline phase.
• a preferred glass matrix of oxyfluorides consisting essentially of NAS glass (Na O-Al 2 O 3 SiO 2 ).
• NAS as host glass shows favorable properties with respect to melting and forming, good transparency and excellent durability.
• the content of SiO preferably is between 30 mol% to 90 mol% of the mols of the glass, preferably between 50 mol% and 80 mol%. The higher the SiO 2 content in the glasses the more viscous they get and the easier they can be formed into large blocks. However, the fluorine retention is less than in glasses which have a SiO content towards the lower limit.
• the SiO can be replaced e.g. by GeO 2 and Al 2 O 3 by Ga O 3 .
• the alkali content (Na 2 O) can be replaced fully or partly by other alkalis, mixture of alkalis or alkaline-earths such as BaO. Many other ingredients can be added to the NAS glass in order to modify and tailor the refractive index, expansion, durability, density and color of the glass matrix.
• the crystal phase in the oxyfluorides comprises LaF 3 .
• LaF 3 -glass ceramics can be achieved by heat treating tempering Al 2 O 3 rich NAS glass saturated with LaF 3 .
• the solubility of LaF is determined by the Al 2 O in the glass.
• LaF 3 levels far below the solubility limit results in stable glasses that do not form glass ceramics when heat treated. Therefore the content of LaF in the glass has to be within ⁇ 15 %, preferably 10 % of the solubility limit of LaF .
• the solubility of LaF 3 is raised. Therefore the amount of LaF 3 should be increased.
• LaF 3 glass ceramics shows a chemical resistance which is in many aspects better than glass ceramics used before, e.g. ZBLAN glass ceramics.
• the LaF 3 crystal phase allows the partition of any rare earth. Therefore a huge variety of up- and down converting luminescent materials with very unusual electronic structures can be provided by substitution of part or all of the La 3+ by other rare earth ions, which are responsive to excitation radiation not commonly used in established document and product security phosphors.
• the use of glass ceramic luminescent materials in combination with two- or multi- photon excitation according to the advanced product security system of the present invention substantially broadens the palette of available luminescence able to emit in up-converting mode.
• the oxyfluoride glass ceramics is transparent and colorless to the human eye.
• the microstructure of the LaF glass ceramics is a function of the heat treatment temperature.
• 750°C for 4 h a large number of relatively small (ca. 7 nm) LaF 3 crystals are visible. The higher the temperature the crystallites grow larger.
• 800°C the average crystal has a dimension of 20 nm (longest room axis?) and at 825°C over 30 nm average crystallite size are observed. Since one influence factor for transparency is the appropriate crystallite size, the glass ceramics which was formed on 750°C for 4 h resulted in the most transparent of all.
• the tempered glass ceramic can be ground to pigment.
• Optimal particle size for most printing applications is in the order of 3 to 10 ⁇ m.
• an invisible product coding can be applied to a substrate. Since the oxyfluoride glass ceramic pigments can be designed with emission properties which do not respond to the excitation radiation of commonly used wavelengths it becomes very difficult for a potential counterfeiter to localize and identify the marking or to retro- engineer the pigment.
• the further wavelengths can either be the same as the first and/or the second wavelength or can be different at all.
• An alternative method for authentication of a security article comprises the steps of:
• a still alternative method for authentication of a security article comprises the steps of:
• the up-converting material in step a is at least part of the security marking applied and/or incorporated in the security article.
• Part of the present invention further is a security marking providing an electromagnetic emission of a certain wavelength as a authenticating feature, said electromagnetic emission being produced as emission from an anti-stokes material as a result of excitation of said anti-stokes material by electromagnetic radiation of at least two different wavelengths.
• the security marking is part of a security article.
• Figure 1 shows a schematic representation of a product security system embodying an up- converting material and a authenticating equipment comprising two sources of electromagnetic radiation and a detecting device.
• Figure 2 shows a schematic representation of the energy levels and optical transitions in up- converting materials representing a) a material with equally spaced energy levels, suitable for single wavelength excitation (state of the art) and b) a material with energy levels of different distance requiring multi-wavelength, at least two wavelength excitation.
• Figure 1 shows a authenticating equipment 1 which is part of the product security system of the present invention.
• Two laser diodes 2 and 3 which are capable of emitting radiation having two different wavelength ⁇ 2 and ⁇ 3 are provided. Their light is led to an optical system 4 by two dichroic minors, 5 and 6 and then focused on a marking 7 comprising up-converting material.
• the marking 7 is applied to the surface of a product 7a.
• the response signal of the marking 7 is focused by the same optical system 4 and passing the dichroic mirrors 5 and 6 directed through a filter 10 to a photodetector 8.
• This embodiment with two excitation sources allows efficiently to obtain up- conversion signals from anti-Stokes materials which do not have equally spaced energy levels in its electronic structure.
• a micro controller circuit 9 is connected to a power supply 12 and activates the pulse lasers 2 and 3 with an appropriate excitation timing sequence.
• the controller circuit 9 also receives the output from the photodetector 8 to evaluate the up-converting response signal.
• the purpose of the filter 10 is to select the appropriate wavelength of the response signal.
• a display 11 may be provided for indicating the result of the authentication operation.
• Figure 2 shows schematically two electron energy level situations which are encountered in rare earth ion based up-converting materials.
• Fig. 2a shows the energy level scheme of a material having approximately equally spaced energy levels. Such materials are suitable for single wavelength excitation.
• ytterbium(3+) acts as a sensitizer ion and erbium(3+) as an activator ion.
• an ytterbium ion is promoted from its ground state ( 2 F 7/2 ) to a first excited state ( 2 F 5 / 2 ).
• the energy of the excited Yb 3+ is subsequently transferred to an Er 3+ ion, promoting it from its ground state ( 4 I 15 / 2 ) to a first excited state (% 2 ).
• a first excited state % 2
• IR radiation 980 nm wavelength
• This second excited state decays in a non radiative way to the long-lived 4 S 3/ state which, in turn, decays to the Er 3+ ground state ( 4 I ⁇ 5/2 ) under emission of green light of 550 nm wavelength.
• Fig. 2b shows the energy level scheme of an up-converting material with unequally spaced energy levels as they are comprised in the marking 7 of Fig.1.
• Such materials require two- or multi- wavelength excitation, using a combination of two or several lasers.
• the luminescent host matrix is LaF 3 :Pr, the crystalline component of the glass ceramic in question. Irradiation of the material with IR radiation of a first preselected wavelength (1014 nm) promotes part of the Pr 3+ ions from the 3 H 4 ground state into the 1 G 4 excited state. From this latter, no further excited state can be reached with 1014 nm radiation.
• the pulsed excitation of the up-converting material has to occur in appropriate coincidence in space and time, in order to guarantee the success of the second excitation, which must occur during the life-time of the first excited state population.
• a time delay in the region of 0.1 ⁇ s to 1000 ⁇ s between the pulses of different wavelengths can prove useful, in order to allow the material to undergo determinate internal energy transfer processes, which result in the population of a desired excited state.
• two or multi- wavelength pulse excitation with appropriate time delays offers a way to design and identify even more specifically identifiable luminescent materials.

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• 2000
  • 2000-01-10 EP EP00810018A patent/EP1117060A1/en not_active Withdrawn
  • 2000-12-21 HU HU0301570A patent/HUP0301570A2/hu unknown
  • 2000-12-21 KR KR1020027008915A patent/KR100750574B1/ko not_active IP Right Cessation
  • 2000-12-21 MX MXPA02006792A patent/MXPA02006792A/es active IP Right Grant
  • 2000-12-21 WO PCT/EP2000/013062 patent/WO2001052175A1/en not_active Application Discontinuation
  • 2000-12-21 PT PT00987429T patent/PT1247245E/pt unknown
  • 2000-12-21 JP JP2001552325A patent/JP2003524839A/ja active Pending
  • 2000-12-21 DK DK00987429T patent/DK1247245T3/da active
  • 2000-12-21 EP EP00987429A patent/EP1247245B1/en not_active Revoked
  • 2000-12-21 RU RU2002121492/09A patent/RU2261479C2/ru not_active IP Right Cessation
  • 2000-12-21 CN CNB008182922A patent/CN1205586C/zh not_active Expired - Fee Related
  • 2000-12-21 CZ CZ20022355A patent/CZ20022355A3/cs unknown
  • 2000-12-21 ES ES00987429T patent/ES2208458T3/es not_active Expired - Lifetime
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  • 2000-12-21 TR TR2003/02264T patent/TR200302264T4/xx unknown
  • 2000-12-21 DE DE60006004T patent/DE60006004T2/de not_active Revoked
  • 2000-12-21 NZ NZ520039A patent/NZ520039A/en unknown
  • 2000-12-21 CA CA002394879A patent/CA2394879A1/en not_active Abandoned
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  • 2002-07-09 ZA ZA200205454A patent/ZA200205454B/xx unknown
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