A security element comprising a first and a second pattern PAT1 and PAT2 formed in or on a substrate, the first pattern PAT1 being formed by a first material INK1 applied to a first region of the substrate, the second pattern PAT2 being formed by a second material INK2 applied to a second region of the substrate, said first and second regions of the substrate overlapping,

wherein a part of the first pattern PAT1 overlaps with a part of said second pattern PAT2, the first material INK1 comprises a first luminescent dye or pigment DYE1, which upon excitation by electromagnetic radiation falling within an excitation wavelength range 1a of the first luminescent dye or pigment DYE1 is capable of emitting electromagnetic radiation in at least one first emission wavelength range 1e, and the second material INK2 comprises a second luminescent dye or pigment DYE2, which upon excitation by electromagnetic radiation falling within an excitation wavelength range 2a of the second luminescent dye or pigment DYE2 is capable of emitting electromagnetic radiation in at least one second emission wavelength range 2e, and said first emission wavelength range 1e of the first luminescent dye or pigment DYE1 overlaps with the excitation wavelength range 2a of the second luminescent dye or pigment DYE2, so that upon irradiation with electromagnetic radiation within the excitation wavelength range 1a of the first luminescent dye or pigment DYE1 the second luminescent dye or pigment DYE2 is excited, in the area of overlap of the patterns, to emit electromagnetic radiation in the emission wavelength range 2e.

A method of illuminating an item is disclosed. The method includes applying adhesive to the item, interspersing a taggant in the adhesive, illuminating the item with an excitation signal, sensing luminescence emitted by the taggant in response to illumination by the excitation signal, and determining the authenticity of the item based on the sensed emitted luminescence. The item can include any item benefited by authentication, and can include a postage stamp. A method of customizing an item is disclosed. This can include the steps of preparing a substrate, applying a security feature to the substrate, printing non-customized information on the substrate, receiving image information, and printing the image information on the substrate.

A method of illuminating an item is disclosed. The method includes applying adhesive to the item, interspersing a taggant in the adhesive, illuminating the item with an excitation signal, sensing luminescence emitted by the taggant in response to illumination by the excitation signal, and determining the authenticity of the item based on the sensed emitted luminescence. The item can include any item benefited by authentication, and can include a postage stamp. A method of customizing an item is disclosed. This can include the steps of preparing a substrate, applying a security feature to the substrate, printing non-customized information on the substrate, receiving image information, and printing the image information on the substrate.

A security document with unidirectional visual illumination is disclosed. A security feature is positioned within the document and not visible in normal ambient lighting conditions but becomes visible under specialized lighting conditions, for example in the presence of ultraviolet light. The security feature is constructible such that it is visible only from a single side of the security document, with the side being predeterminable regardless of the orientation of the specialized light.

A security document with unidirectional visual illumination is disclosed. A security feature is positioned within the document and not visible in normal ambient lighting conditions but becomes visible under specialized lighting conditions, for example in the presence of ultraviolet light. The security feature is constructible such that it is visible only from a single side of the security document, with the side being predeterminable regardless of the orientation of the specialized light.

A plastic card includes a multi-layer card body into which is integrated a window-type security feature. The card body includes a core layer that is laminated between top and bottom opaque print layers. The security feature includes a transparent insert incorporated into the core layer that serves as a light-transmissive card window. Overt and covert print elements are printed onto the top and bottom surfaces, respectively, of top print layer in alignment with the clear insert, with only the overt print element visible in natural light. By contrast, covert print element is only viewable by illuminating the partially light-transmissive top print layer through the insert. Preferably, the overt and covert print elements are tightly nested design elements that render the resulting harmonized image more difficult to replicate by unscrupulous individuals. Additionally, the insert is preferably dosed with a UV brightener to provide a forensic-level of security to the plastic card.

A plastic card includes a multi-layer card body into which is integrated a window-type security feature. The card body includes a core layer that is laminated between top and bottom opaque print layers. The security feature includes a transparent insert incorporated into the core layer that serves as a light-transmissive card window. Overt and covert print elements are printed onto the top and bottom surfaces, respectively, of top print layer in alignment with the clear insert, with only the overt print element visible in natural light. By contrast, covert print element is only viewable by illuminating the partially light-transmissive top print layer through the insert. Preferably, the overt and covert print elements are tightly nested design elements that render the resulting harmonized image more difficult to replicate by unscrupulous individuals. Additionally, the insert is preferably dosed with a UV brightener to provide a forensic-level of security to the plastic card.

A method of illuminating an item is disclosed. The method includes applying adhesive to the item, interspersing a taggant in the adhesive, illuminating the item with an excitation signal, sensing luminescence emitted by the taggant in response to illumination by the excitation signal, and determining the authenticity of the item based on the sensed emitted luminescence. The item can include any item benefited by authentication, and can include a postage stamp. A method of customizing an item is disclosed. This can include the steps of preparing a substrate, applying a security feature to the substrate, printing non-customized information on the substrate, receiving image information, and printing the image information on the substrate.

A method of illuminating an item is disclosed. The method includes applying adhesive to the item, interspersing a taggant in the adhesive, illuminating the item with an excitation signal, sensing luminescence emitted by the taggant in response to illumination by the excitation signal, and determining the authenticity of the item based on the sensed emitted luminescence. The item can include any item benefited by authentication, and can include a postage stamp. A method of customizing an item is disclosed. This can include the steps of preparing a substrate, applying a security feature to the substrate, printing non-customized information on the substrate, receiving image information, and printing the image information on the substrate.

A new concept of bi-luminescent security pigments includes lanthanide doped rare-earth compound with rare-earth free compound and its ink formulation. The unique features of this bi-luminescent security ink is that it emits two different colors when it is illuminated by using two different excitation wavelengths. This important feature makes it most suitable for printing of security codes or QR codes/security images on currency, important official documents, food and medicinal packaging etc. The prospective use of this bi-luminescent security ink provides a ground-breaking opening for easily printable, highly stable and unclonable bi-luminescent security codes for anti-counterfeiting applications.