This article is part of a continuing series that looks at security features in development for the security paper industry.
The security paper industry is no stranger to the use of fluorescence. Often used in banknotes, fluorescence provides a unique security device that can only be revealed under ultra violet (UV) lights.
On the Canadian $20 bill, for example, the words “Bank of Canada/Banque du Canada” glow red and yellow on the bill’s left side when placed under UV lights. Similarly, a security thread on the US $100 bill containing the text “USA 100” glows red under UV lights. Numbered panels printed in fluorescent ink on Indian rupees can also only
be detected under UV lights.
Scientists from the Fraunhofer Institute for Applied Polymer Research, however, are finding new ways to use fluorescence in way that is not only new and revolutionary, but also more secure.
Instead of adding individual fluorescent devices on one specific part of the banknote, researchers at Fraunhofer are testing ways to add fluorescent dyes to the entire banknote.
To understand how this research may prove to be revolutionary, you first have to understand how fluorescence works.
Professor Julian Gray of the Georgia Mineral Society explains:
“Minerals are composed of atoms, which in turn contain electrons at specific energy levels. Ultraviolet light is an energy source. When we shine an ultraviolet lamp on a mineral that fluoresces, the atoms that make up the mineral absorb energy from the light by moving electrons to higher energy levels. However, the electrons cannot remain in this unstable, excited state. When the energized electrons return to the original lower energy level, they give back the difference in energy by emitting visible light. This is what causes the mineral to produce light. As long as the ultraviolet lamp energy source is on, electrons are continually jumping from lower to higher energy levels and back, in the process producing the wonderful fluorescent colors that we see. If the mineral only produces light when ultraviolet light is shining on the mineral, this is called fluorescence.”
When it comes to security devices, typically only one or two mineral dyes are used to create the feature. Since various dyes react to different properties, the researchers at Fraunhofer decided to add multiple dyes to the whole banknote producing “an individualized marker” that is “exceedingly difficult to imitate.”
Moreover, because the mixture of dyes is a not only unique (and presumably one that will be kept secret) but is also relatively minimal (just a few parts per billion), researchers assert that it will be “virtually impossible to decode the type and quantity of the dye additives thus making the product counterfeit proof.
Because the dye is added to the entirety of the banknote, counterfeiters cannot remove the feature. Whereas fluorescent spots can – in theory – be removed from a secure document, say researchers, this feature permeates the entire material and is “itself a component of the identification label.”
Beside counterfeit protection, the process is also suitable for an effective quality assurance, such as with coatings: With the aid of various dyes, manufacturers can monitor the chemical composition, degree of dryness and the thickness of the coat during the production process.
Dr. Andreas Holländer, one of the scientists at Fraunhofer, says if this fluorescent security device is adopted by the security paper industry, the key to its success will be the creation of dye mixtures specific to individual products so a standard solution for products across the board would be highly discouraged.
“One reason for the high degree of security of our technology is precisely because there are only material-specific solutions,” says Holländer.
Nanowerk: “Brilliant Counterfeit Protection”
Science Learning: “UV and Fluorescence”
Bank of Canada
Banknote.org: “USA Banknotes’ Security Features”
Reserve Bank of India: “Fluorescence”
Georgia Mineral Society: “Fluorescence by Julian C. Gray”