Patent ID: 7449698

Claim:
A method for coding a luminescent tag comprising a composition of at least two luminescent compounds, each one of which luminescing within at least one luminescence band, said luminescent compounds comprising at least one donor compound and at least one acceptor compound, an emission spectrum of said donor compound overlapping with an absorption spectrum of said acceptor compound, the method comprising steps of: providing a reference tag representative of reference relative light intensities emitted within at least two luminescence bands; initially irradiating said luminescent tag with a low power source of electromagnetic radiation such that said luminescent tag emits initial relative light intensities; and coding said luminescent tag by irradiating said luminescent tag with a high power source of electromagnetic radiation and adjusting an energy of said high power source of electromagnetic radiation such that when said luminescent tag is subsequently irradiated with a subsequent low power source of electromagnetic radiation measured relative light intensities emitted by the luminescent tag are modified with respect to the initial relative light intensities to match said reference relative light intensities of said reference tag, said high power source of electromagnetic radiation comprising a wavelength which lies within an absorption spectrum of said donor compound.