Security device
A security device with multiple layers. A substrate provides the backing to a first luminescent layer. An optically variable structure is positioned between the first luminescent layer and a second luminescent layer. Both the first and second luminescent layers emit luminescent radiation when stimulated. When the first layer is stimulated, the optically variable structure filters the emitted luminescent radiation such that the emitted luminescent radiation only escapes the optically variable structure at a predetermined range of emission angles. A user, when viewing the security device from the predetermined range of angles as both layers are stimulated, can see a completed image of a predetermined indicia. When the security device is viewed at angles other than the predetermined range of angles as both layers are stimulated, a user will only see an incomplete image of the predetermined indicia.
1. A security device comprising:
luminescent materials in distinct, non-overlapping regions of the device from one another, that are the same or different from one another, with no overlap between any luminescent materials, that when stimulated emit luminescent radiations from the distinct, non-overlapping regions of the security device;
an angle-dependent optical filter coupled to one of the luminescent materials so that luminescent radiation emitted therefrom is transmitted through and emitted from the filter only at certain angles, to selectively coincide with luminescent radiation emitted from another of the luminescent materials, thereby to form a composite image comprising the luminescent radiations emitted from the luminescent materials in said distinct, non-overlapping regions of the device only when the device is viewed at said certain angles.
2. The security device of claim 1 , wherein the luminescent materials, when stimulated, emit luminescent radiations having different wavelengths from one another.
3. The security device of claim 1 , wherein the angle-dependent optical filter, after filtering the luminescent radiation of the coupled luminescent material, emits luminescent radiation of the same wavelength as unfiltered luminescent radiation emitted from the other luminescent material(s).
4. The security device of claim 1 , wherein the composite image forms one or more letter, number, icon or picture.
5. The security device of claim 1 , wherein at least two of the luminescent materials are separated from one other by the angle-dependent optical filter, which overlies the luminescent material to which it is coupled, so that luminescent radiation emanating from the coupled luminescent material passes through the angle-dependent optical filter, whereas the luminescent radiation emanating from at least one of the other luminescent materials does not pass through the angle-dependent optical filter.
6. The security device of claim 1 , wherein the angle-dependent optical filter comprises a chromatic filter, an optical interference structure, or a Fabry-Perot optical cavity.
7. The security device of claim 1 , wherein the angle-dependent optical filter selectively modifies the emission of the luminescent radiation from one of the luminescent materials, but not the others.
8. The security device of claim 1 , further comprising one or more further luminescent materials each, when stimulated, emitting further luminescent radiations from the device, so that the luminescent radiations selectively coincide with one another to form one or more composite images when the device is viewed at different angles.
9. A security document comprising:
a. a substrate; and
b. one or more security devices of claim 1 attached thereto, or integrated therein.
10. The security document of claim 1 , wherein the substrate comprises a polymer.