B. Baloukas and L. Martinu, Département de génie physique, École Polytechnique de Montréal
Counterfeiting of products and important documents is at an all-time high and is costing the world economy hundreds of billions of dollars yearly as well as posing significant safety and health hazards through the production of uncertified goods, e.g., pharmaceutical products. To limit these effects, interference-based optical security devices offering an angular color shift are still widely in use. Unfortunately, commercial iridescent materials are now readily available and represent a potential source of counterfeiting.
In this short talk, we first briefly introduce the activities in our Functional Coatings and Surface Engineering Laboratory (FCSEL). We then describe the basic principles behind passive interference security image structures and the qualities which have resulted in their integration into most currently in use important documents.
Emphasis will then be put on active materials which have recently been proposed as a means of augmenting present-day passive technologies. While there exist many possibilities, electrochromic (EC) materials are particularly interesting candidates. We focus our discussion on WO3 and present various examples where the use of this material in different nanostructured forms can lead to innovative optical effects with an emphasis on the electrochromic performance of individual films as well as when implemented into more complex structures.
Finally, we demonstrate that these innovative structures not only possess an EC color change but also an angular color shift. While these characteristics make them interesting candidates for security features possessing two levels of authentication, they may also be of interest for applications such as EC windows and others.
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