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Europium (III) oxide (Eu2.O3), glowing pink under ultraviolet (UV) light. Europium, one of the chemical elements, is a lanthanide in period 6, and the f-block of the periodic table. The lanthanides are also referred to as the rare earth elements. This oxide contains europium in its +3 oxidation state. It is the presence of europium in this oxidation state that produces fluorescence with this specific colour under ultraviolet light. This property of europium (III) compounds is used in banknotes for anti-counterfeiting markers, and in television sets and fluorescent lights. (KEYSTONE/SCIENCE PHOTO LIBRARY/SCIENCE PHOTO LIBRARY)