Method for identifying articles and process for maintaining security

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The invention is directed to a method by exposing at least a portion of a luminescent coating disposed on a surface of an article to ultraviolet light at one or more preselected wavelengths causing said luminescent coating to exhibit a luminescence spectrum, the luminescence spectrum exhibiting a plurality of intensity peaks that have been priorly determined to create a standard; determining the intensity of at least two peaks in the luminescence spectrum of the coating; determining a peak intensity ratio of the at least two peaks; comparing the peak intensity ratio determined with the standard; and, classifying the article according to whether or not the peak intensity ratio does or does not match the standard; wherein the luminescent coating comprises a particulate luminescent composition comprising a rare earth doped fluoride represented by the formula          RExA1-xF2+x-2yOy wherein RE represents a three-valent rare-earth element, A is alkaline earth, 0.002 ≤ x ≤0.20, and 0 ≤y ≤x.