| 主权项 |
1. A method of verifying the authenticity of an image article, the method comprising exposing said image article to radiation having a wavelength of between 800 and 900 nm, and measuring the reflectance of said radiation; wherein the image article comprises a substrate having a security image coated on at least a portion thereof, which security image effects less than 50% reflectance of radiation of a wavelength between 800 and 900 nm, wherein the security image comprises an infrared-absorbing compound selected from: or a salt or polymer thereof, wherein
M is a metal selected from a group 3-10 (Group IIIB-VIII) element or a lanthanide;R1 is selected from hydrogen, phosphonate, sulphonate, nitro, halo, cyano, thiocyano, thioalkyl, thioaryl, alkyl, alkoxy, aryl, aryloxy, amines, substituted amines and substituted aryl;one of R2 and R3 is oxygen and the other of R2 and R3 is NO;n is a number corresponding to half the co-ordination number of the metal M;each L and L′ is independently a ligand complexed to the metal M; andy is a number corresponding to the co-ordination number of the metal M; wherein said infrared-absorbing compound does not create a strongly coloured security image. |
