Patent EA-004580-B1 (EA)
Title: Luminescence characteristics detector
Inventor: VASIC MILAN
IPC: B44F1/12
Filed: 2002-01-26
Abstract: 1. Method for authenticating a security marking comprising a luminescent compound by exposing the marking to an excitation, said luminescent compound being excitable by an excitation light source and measuring the intensity of the luminescence emission wherein during or after exposure to the excitation light source light-intensity values are measured during intervals of time (t1, t2, t3,t4, t5, t6, t7, t8) which are selected that, after subtracting the intensity value collected during one time interval from the intensity value collected during another time interval, the result of the subtraction is representative for light emitted from the luminescent material. 2. Method according to claim 1, wherein one of the time intervals (t5) is selected during the initial phase of the excitation of the luminescent material to reduce the proportion of light intensity (2a) resulting from emission of the luminescent material compared to measured light intensity (1a) caused by back-scattering light, stray light or other light which does not result from emission. 3. Method according to claim 1 or 2 wherein a second time interval (t6) is selected during a phase in which the intensity resulting from emission of the luminescent material has risen to its maximum. 4. Method according to claim 2 or 3 wherein the duration of one time interval(t5, t6) is shorter than 25% of the emission period (A). 5. Method according to one of the preceding claims wherein the marking comprises one or more luminescent compounds which emit light at two different frequencies and intensity values are sampled for light emitted at said frequencies. 6. Method according to claim 5 wherein the intensity values of said different frequencies are compared. 7. Method according to one of the preceding claims wherein light intensity is sampled during exposure of the marking to irradiation. 8. Method according to one of the preceding claims wherein light intensity is sampled after exposure of the marking to irradiation. 9. Method according to one of the preceding claims wherein the light intensity values during the time periods (t1 to t8) are integrated. 10. Method for the marking and authenticating of security documents or articles, said method relying on the use of at least one luminescent compound, said luminescent compound being excitable by an excitation light source and showing a build-up in time of the luminescence emission intensity after the excitation light source has been switched on, and a decay in time of the luminescence emission intensity after the excitation light source has been switched off, said method being characterized in that - said luminescent compound is part of a security document or article, and - said excitation light source is switched on during a first time interval (T1) and switched off during a second time interval (T2), and - at least two luminescence intensity values are measured for at least one luminescence wavelength at least during two subsequent time intervals (T3, T4) inside either time interval (T1) or time interval (T2) or both, and - at least two of said measured luminescence intensity values are subtracted from each other to obtain net luminescence intensity values, which are compared to reference values, as an authenticity criterion. 11. Method according to claim 10 wherein time intervals (T3, T4) are equal and comprised within time interval (T1). 12. Method according to claim11 wherein time intervals (T3, T4) are half of time interval (T1). 13. Method according to claim12 wherein time intervals (T3, T4) are equal and comprised within time interval (T2). 14. Method according to claim13 wherein time intervals (T3, T4) are half of time interval (T2). 15. Method according to one of claims 10 to 14, wherein said excitation light source is repeatedly switched on and off, and wherein said luminescence intensity values are repeatedly measured and subtracted, to obtain integrated net intensity values, which are compared to reference values, as an authenticity criterion. 16. Device for the authentication of security documents or articles, said documents or articles carrying at least one luminescent compound, said luminescent compound being excitable by an excitation light source and showing a build up in time of the luminescence emission intensity after the excitation light source has been switched on, and a decay in time of the luminescence emission intensity after the excitation light source has been switched off, said device comprising at least one excitation light source, at least one photodetector channel, and at least one microprocessor, said device being characterized in that - said excitation light source is capable of being switched on during a first time interval (T1) and of being switched off during a second time interval (T2) under control of said microprocessor, and - said photodetector channel comprises at least one photodetector, producing an analog output signal when illuminated by a light source, and at least one signal sampling unit, capable of sampling and integrating, under control of said microprocessor, non-inverted (P1) and inverted (P2) portions, respectively, of said photodetector output signal during time intervals (T3,T4), producing at least one net output signal, and - said microprocessor is capable of digitizing and storing said at least one net output signal. 17. Device according to claim 16, wherein time intervals (T3,T4) are equal and comprised within time interval(T1). 18. Device according to claim 17 wherein time intervals (T3, T4) are half of time interval (T1). 19. Device according to claim 18, wherein time intervals (T3,T4) are equal and comprised within time interval (T2). 20. Device according to claim 19 wherein time intervals (T3, T4) are half of time interval (T2). 21. Device according to one of claims 13 to 20, wherein said excitation light source is repeatedly switched on and off, and wherein said signal sampling unit is repeatedly sampling and integrating said photodetector output signal, obtaining at least one integrated net output signal. 22. Device according to one of claims 20 to 21, wherein said at least one net output signal or said at least one integrated net output signal is locally compared by said microprocessor with at least one internally stored reference value, to derive an authenticity signal. 23. Device according to one of claims 20 to 22, wherein said at least one net output signal or said at least one integrated net output signal is transmitted via a communication link to a remote server, to be compared with at least one stored reference value, to derive and send back an authenticity signal. 24. Security system comprising a number of luminescent markers having time-deferred emission characteristics and preferably different emission wavelengths, to be incorporated at different ratios into inks or plastic materials for the production of security documents or articles, and a device according to one of claims 20 to 23, preferably having a corresponding number of detecting channels, for determining the authenticity of said security documents or articles. 25. Authentication device comprising a device to emit irradiation light to a marking, a device to measure light intensity during at least two time intervals, a device to substract values of light intensity and to provide output signals for performing the method according to one of the claims 1 to 13. 26. Device according to claim 25 comprising a device to measure light intensity of a two or more frequency range of the light. 27. System comprising an authentication device according to claim 25 or 26 and a composition to create a security marking comprising luminescent material which is capable to be detected by said authentication device.