Security system with different size emissive particles

摘要

A security marker material comprising emissive particles selected from at least two groups with different size distributions and the size distributions satisfy the formula: [(x−z)2/(Sx2 +Sz2)]1/2 >1 wherein x and z are the volume-weighted mean equivalent-spherical diameters of the two particle distributions and Sx and Sz are the standard deviations of the same two distributions. The emissive materials are placed in or on an item. The emissive materials are excited with electromagnetic radiation in one or more specified spectral bands. The electromagnetic radiation is detected in one or more spectral bands from the emissive materials in an image-wise fashion. The attributes of the image are analyzed and characterized and are compared to authentication criteria to determine the authenticity of the marked item.