Euro is an important and high profile international currency. This makes it a perfect target for counterfeiters. The banks are well-aware of this fact and they take special preventive measures to tackle the forgery of the currency. But, with modern technologies, preventing fraud to imitate the notes is a tough task.

Source: Wikipedia

Thanks to Europium for providing an anti-counterfeiting option for the Euro banknotes.

Source: Schloss

Europium is a luminescent material the bank uses in their currency. This chemical makes the Euro notes illuminate when exposed to UV light. According to a report in Fleur De Coin, you can notice the following characteristics when the note is put under ultra-violet (UV) light:

1. The fibres embedded in the paper are fluorescent and are visible in three colours (red, blue and green).

2. On the front of the banknote, two inks become visible: the blue ink becomes green and the yellow ink becomes orange. The European flag and the signature of the ECB President are green and the stars are orange. Other features on the front of the banknote will also be visible; however, this will vary between the different denominations.

3. On the reverse side, only one ink will be visible. The map of Europe, the bridge and the denomination appear in yellow.

Source: Imgur

It is one of the more expensive lanthanides (the series of chemical elements comprising of the fifteen metallic chemical elements with atomic numbers 57 through 71). This is probably a factor in its usage to prevent against forgeries.

And yes, Euro notes using the chemical Europium is just a hilarious coincidence.