Luminescence characteristics detector
AssigneeSicpa Holding SA
InventorsMilan Vasic, Edgar Muller, Myron Seto
Life of this patent
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Abstract
Security documents or articles carrying luminescent marker compounds which show a time-deferred emission characteristic are authenticated by a method and device which allows for rapid extraction of characteristic luminescent parameters, such as emission intensity and time constants. The method is not sensitive to perturbations by ambient light and reduces optical filtering requirements.
Claims28
A 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 specific intervals of time 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 compound, wherein the duration of one time interval is shorter than 25% of the duration of the exposure of the luminescent compound to the excitation light source.
A method for marking and authenticating 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, wherein
- said luminescent compound is part of a security document or article, and said method comprises steps of
- switching said excitation light source on during a first time interval and off during a second time interval,
- measuring at least two luminescence intensity values for at least one luminescence wavelength at least during two subsequent third and fourth time intervals inside either first time interval or second time interval or both, wherein the duration of one of said third and fourth time intervals is shorter than 25% of the duration of the exposure of the luminescent compound to the excitation light source, and
- subtracting at least one of said measured luminescence intensity values from another such value to obtain net luminescence intensity values, and
- comparing said net luminescent intensity values to reference values, as an authenticity criterion.
A device for authenticating 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 luminescent emission intensity after the excitation light source has been switched on, and a decay in time of the luminescent 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, wherein
- said excitation light source is capable of being switched on during a first time interval and of being switched off during a second time interval under control of said microprocessor,
- 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 micro-processor, non-inverted and inverted portions, respectively, of said photodetector output signal during third and fourth time intervals, wherein the duration of one of said third and fourth time intervals is shorter than 25% of the duration of the exposure of the luminescent compound to the excitation light source, producing at least one net output signal, and
- said microprocessor is capable of digitizing and storing said at least one net output signal.
Dependencies are inferred from the claim text.