Patent ID: 7622163

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 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 RE x A 1−x F 2+x−2y O y wherein RE represents a three-valent rare-earth element, A is alkaline earth, 0.002≦x≦0.20, and 0≦y≦x.