Yes, thulium is used in Euro banknotes to prevent counterfeiting. The element in the note displays blue fluorescence under ultraviolet light thus aiding in distinguishing between the real and the fake currency note.
Thulium gets its name from the name of an ancient place called Thule which is associated with Scandinavia. Per Teodor Cleve, the Swedish chemist discovered two new materials, one green and one brown, while working with erbia (erbium oxide) in 1879, in Uppsala, Sweden. These turned out to be oxides of two new elements: thulium and holmium. The green substance he named thulia, which he later found to be thulium oxide, and the brown substance he named holmia, which he later found to be holmium oxide. Charles James in New Hampshire prepared the first pure thulium in 1911.
This element does not have many uses as it is rare, and therefore, costly. There are many cheaper elements that can substitute thulium. It is used in laser equipment and X-ray devices. The atomic number of thulium is 69, and its atomic symbol is Tm.
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