Characterization of Rare Earth Elements in Scheelite (CaWO4) with Ion Beam Induced Luminescence

Scheelite is a calcium tungstate mineral (CaWO4) well known in the mining industry as a source of tungsten. This mineral fluoresces under shortwave UV and X-rays excitation with a characteristic blue luminescence centered at about 425 nm. CaWO4-based powder was commonly used as blue phosphor and scintillator (due to high Z of W) [1-3]. The emitted spectrum shifts to yellow in the presence of molybdenum in place of tungsten. Scheelite’s crystal system is tetragonal and its crystals appear as dipyramidal pseudo-octahedra where the structural unit is an atom of tungsten surrounded at four corner of the tetrahedron by four oxygen atoms. Color of crystals may vary from yellow, to green, to reddish. This mineral is usually found in association with small amounts of molybdenum and rare earth elements whose characterization give useful information to define the mineral formation process like: • geological phenomena that due formation of the mineral; • physico-chemical conditions of transport or precipitation of the ore, • identification of the source of the ore [4]. The aim of this work is to evaluate the effectiveness of Ion Beam Induced Luminescence (IBIL) in the characterization of rare earth elements into scheelite by probing samples collected in different Italian sites.