Blog: There’s europium in euros

Unfortunately, with all that is happening, I seemed to have taken my eye off of sharing some interesting ‘Hey, what are the rare earths and where are they used?’ pieces. So here goes…

Some of us will remember that in early 2000, several European countries abandoned their old currencies and switched to the Euro.  As most of us know, bank notes are prime targets for counterfeiters. But did you know that the application of luminescence is one of the measures that guard against this kind of mayhem? Well, I was reminded of the aplication yesterday afternoon by Professor Andries Meijerink of the University of Utrecht, at one of the pre-conference seminars at Phosphor Global 2010 (I’ll be speaking later this morning on the delicacy of the global REE supply-demand balance)

Professor Meijerink noted that some years ago, researchers at the Department of Chemistry at Utrecht University were curious about what caused the luminescence of the Euro notes and guess what they found? … Yup!  Europium.

Europium (Eu), one of the rare earth elements (or lanthanides) and that most of the trivalent REEs are luminescent. This means that ions within these materials can be excited by shining a light of a particular wavelength at them. When the ions relax again, they emit light – of a different wavelength. That is luminescence.

As noted in an article posted on the website, “The luminescence of the REEs is unique: relatively long-lasting and producing sharp bands. It is therefore a widely used tracer and analytical tool. If you use a very intense excitation source, you can detect very low concentrations of fluorescent compounds. 

Euro notes luminesce in the red, green and blue. The red light is clearly linked to europium and most likely to a Eu3+ according to the Utrecht researchers. They found it less easy to identify the source of the blue and green luminescence. They apparently believe (or at least they did at the time of the initial investigation) that the likely source of the green color is SrGa2S4:Eu2+. As for the blue colour, the researchers suspected that Euro notes printer may integrate (BaO)x.6Al2O3:Eu3+ in some manner or another.

Apparently the Dutch Central Bank would never comment when asked to clarify the technology applied to the euro. Understandable – although I’m not sure I’ll every fully grasp the chemistry and physics that underlie phosphor technologies … save that rare earths provide the keys to CFLs, LEDs, etc, etc. and Oh yeah… the Euro.

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