Method for identifying articles and process for maintaining security

A method comprising, within a first time period, a coater causing to be disposed upon the surface of a first plurality of articles, a first luminescent coating, thereby producing a first plurality of coated articles;

• and, within a second time period, the coater causing to be disposed upon the surface of a second plurality of articles, a second luminescent coating, thereby producing a second plurality of coated articles;
• a classifier causing to be exposed at least a portion of one or more of the first or second plurality of coated articles to ultraviolet light at one or more preselected wavelengths thereby causing the coating to exhibit, respectively a first or second luminescence spectrum, each the first or second luminescence spectrum exhibiting a plurality of intensity peaks the wavelengths of the peaks having been priorly determined using light comprising the preselected wavelength or wavelengths to create a first standard corresponding to the first plurality of coated articles and a second standard corresponding to the second plurality of coated articles;
• determining the peak intensity ratio of at least two of the intensity peaks in the first or second luminescence spectrum of the first or second coating;
• comparing the peak intensity ratio so determined with, respectively, the first or second standard depending upon whether the coated article is from the first or the second plurality of coated articles;
• and, classifying the article according to whether or not the peak intensity ratio does or does not match the first or second standard, respectively;
• each the coating comprising a particulate luminescent composition, comprising a rare-earth-doped alkaline earth 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;
• the particulate luminescent composition exhibiting a luminescence spectrum having a plurality of intensity peaks at characteristic wavelengths.