Security aspects of multiexponential decays

摘要

At least two luminescent materials are intermingled within a security feature. The materials are selected from among a larger set of luminescent materials each having a different individual exponential decay characteristic (decay constant and initial amplitude response to the degree of excitation) for photo-luminescent emission from the respective material following excitation. The ratio of the decay constants for any two materials is greater than or equal to about 1.5. The selected materials are mixed in one of a plurality of predetermined ratios. The combined emissions from the intermingled materials appear, to an unsophisticated measuring device, to have a single exponential decay constant. Based on measurements for the decay of the combined emissions following excitation, estimates of the individual decay constants and associated initial emission amplitudes allow decoding of the particular combination of materials and/or their ratios to validate the security feature, authenticating the article.

主权项

1. A security feature, comprising:
an intermingled luminescent material comprising a plurality of luminescent materials that, when individually excited in an absence of other luminescent materials, each produce emissions with a respective individual exponential decay characteristic, wherein the intermingled luminescent material responds to excitation with emissions at a wavelength having a single, multi-exponential decay characteristic, the single multi-exponential decay characteristic different than all of the respective individual exponential decay characteristics for the plurality of luminescent materials.