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Proceedings Paper

Photo-luminescent quantum dots used for security identification
Author(s): Shoude Chang; Kui Yu; Jiaren Liu
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Paper Abstract

Information retrieval is critical in security technologies such as those for status identification and documentation authentication. Ideally, coding materials should be difficult to locate, impossible to counterfeit, and easy to process. This presentation addresses a novel information retrieval technology with these ideal features of its coding materials: the photo-luminescent (PL) quantum-dots (QD) synthesized via wet-chemistry approaches. As compared to traditional PL materials, they exhibit emission with narrower full width at half maximum, greater brightness, and higher photo-stability; also, their PL wavelength can be easily and accurately tuned via their size, structure, and composition. Due to such a feasible tune-ability, mainly, QDs have demonstrated enormous potential applications in security and defense. When QDs are excited, they can provide coded information with their PL wavelength and intensity. If the coding wavelengths from the QD PL are designed as the Fraunhofer lines, i.e. black lines in solar spectrum, the retrieval system can extract the useful information even under sunshine covering areas. Multi-photon excitation (MPE) technologies can further extend applications of QDs to multi-layer information extraction. For an info-label of 2-millimeter in depth, a MPE system with the depth resolution less than one micro-meter can thus achieve 2 GB resolutions, when a coding material exhibiting 6 PL wavelengths with 10 intensity levels. In general, transparent thin-film coating of QDs can be applied to various substrates, such as documents, fingernails, and military helmets and vehicles. Moreover, QD based security information can be easily destroyed by preset expiration in the presence of timing agents.

Paper Details

Date Published: 9 October 2007
PDF: 9 pages
Proc. SPIE 6741, Optics and Photonics for Counterterrorism and Crime Fighting III, 67410K (9 October 2007); doi: 10.1117/12.736447
Show Author Affiliations
Shoude Chang, National Research Council Canada (Canada)
Kui Yu, National Research Council Canada (Canada)
Jiaren Liu, National Research Council Canada (Canada)


Published in SPIE Proceedings Vol. 6741:
Optics and Photonics for Counterterrorism and Crime Fighting III
Colin Lewis, Editor(s)

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