MACHINE READABLE SECURITY ELEMENTS AND PRODUCTS CONTAINING THEM

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This invention relates to a machine readable luminescent security element and an apparatus and method for checking the luminescent security element. The invention is characterised in that security element contains at least two pigments, the first pigment comprising a first inorganic host lattice doped with a first dopant, that is a first luminescent ion, the second pigment comprising a second inorganic host lattice doped with at least two dopants, the said first dopant and a luminescent rare earth ion to which energy may be transferred non-radiatively from the first dopant in the second inorganic host lattice and which largely quenches the emission from the first dopant in the second inorganic host lattice at one or more emission peaks.