Articles incorporating thermographic phosphors, and methods and apparatus for authenticating such articles

A method for identifying a luminescent material incorporated on or within an article, the method comprising the steps of:

• selectively exposing the article to excitation energy in an absorption band of the luminescent material;
• detecting first emission characteristics of first emitted radiation from the article within an emission band of the luminescent material when the article has a first temperature;
• detecting second emission characteristics of second emitted radiation from the article within the emission band when the article has a second temperature that is different from the first temperature;
• and
• determining whether the first emission characteristics are sufficiently different from the second emission characteristics, wherein determining whether the first emission characteristics are sufficiently different from the second emission characteristics comprises determining whether a first decay time constant of the first emitted radiation is at least about 1 percent different from a second decay time constant of the second emitted radiation for each degree of difference between the first and second temperatures.