Patent ID: 7517564

Claim:
A method comprising 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 wherein the luminescence spectrum exhibits a plurality of intensity peaks that have been predetermined 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 at least two peaks; comparing the peak intensity ratio thereby 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 solid-state solution of alkaline earth fluorides represented by the chemical formula RE x (Ca a Sr b Ba c ) 1−x F 2+x−2y O y wherein RE represents a three-valent rare-earth element, 0.005≦x≦0.20, and 0≦y≦0.2, a+b+c=1, with the proviso at least two of a, b, and c are not equal to zero; the particulate luminescent composition exhibiting a luminescence spectrum having a plurality of intensity peaks at characteristic wavelengths.