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1 April 1998 Laser-induced anti-Stokes luminescence for protection of documents and security papers
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The optical properties of rare earth (RE) ions and theirs application for identification and protection of documents will be discussed. RE ions doped powders e.g. fluoride crystals, oxychlorides, oxyfluorides can be used for security printing as components of applied printing dyes. In described above compounds, the anti-Stokes emission occurs. It means that the conversion from infrared-to-visible has place. When excited with an IR diode laser with (lambda) equals 980 nm, the emission in visible is observed. The are many advantages of such security mean. The RE dyes can be invisible and the emission is induced by 'invisible' light. In order to evoke the emission, the matching between used chemical compound and laser light is necessary. The up-conversion phenomena are very rare and can be observed only in some special compounds made by specialized laboratories.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Halina Podbielska M.D. and Wieslaw Strek "Laser-induced anti-Stokes luminescence for protection of documents and security papers", Proc. SPIE 3314, Optical Security and Counterfeit Deterrence Techniques II, (1 April 1998);

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