Europium: Did you know?

materialsscienceandengineering:

Named for the continent of Europe, this rare earth element is actually used in the ink of the paper bills that the European Union produces. Though the actual dyes used are unknown to prevent counterfeiting, it is known that a fluorescent dye is laced with europium ions, selected so that the europium appears dull under visible light but fluoresces under lasers. 

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