 <unk> europium ( <unk> + ) in small amounts is the <unk> of the bright blue fluorescence of some samples of the mineral <unk> ( <unk> ) . The reduction from <unk> + to <unk> + is induced by irradiation with energetic particles . The most outstanding examples of this originated around <unk> and adjacent parts of northern England ; it was the <unk> found here that fluorescence was named after in 1852 , although it was not until much later that europium was determined to be the cause . 
