Patent ID: 8822954

Claim:
A method of authenticating a photo-luminescent security marking in which an authentic security marking comprises a blend of at least two phosphor materials, the method comprising: a) irradiating the marking with a first excitation radiation of only a first wavelength within a first wavelength range, wherein the first radiation having only the first wavelength excites both a first phosphor and a second phosphor, and measuring at least one selected parameter of light emitted by the first phosphor and the second phosphor within the marking, b) irradiating the marking with a second excitation radiation of only a second wavelength that is within a second wavelength range, wherein the second radiation having only the second wavelength excites only the second phosphor, and measuring the at least one selected parameter of light emitted by the second phosphor within the marking, c) irradiating the marking with a third excitation radiation that includes both the first and second wavelengths, wherein the third radiation having the first and second wavelengths excites both the first phosphor and the second phosphor, and measuring the at least one selected parameter of light emitted by the first phosphor and the second phosphor within the marking, and d) comparing the selected parameters measured in a), b) and c) with corresponding parameters of the known emission characteristic and if the parameters are within prescribed limits verifying the authenticity of the marking.