SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Banknote security. Close-up of a UK twenty-pound sterling (20 GBP) banknote under visible light. This region of the banknote is where an anti-counterfeiting marker has been placed. The marker is only visible under ultraviolet (UV) light. The UV light causes chemicals in the marker to fluoresce, making the marker visible as it glows. The colours depend on the chemicals used. UK and Euro banknotes use compounds of the rare earth (lanthanide) elements europium and terbium. For this image in UV light, with the marker visible, see image C013/2679.
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