| 摘要 |
A security document (1) comprises a substrate (10) including at least one layer of. polymeric material (12, 26) and containing an upconverting fluorescent material (18), and at least one coating (14) containing a refractive pigment applied to the substrate (10). When the security document is exposed to electromagnetic radiation of a particular wavelength, e.g. infra-red, the upconverting material (18) emits a signal of electromagnetic radiation of a shorter wavelength, e.g. visible light, and the coating (14) containing the refractive pigment enhances the signal. |
