Sr 1/2 Ce 5/14 □ 1/7 WO 4 : a new modulated ternary scheelite compound.

For the first time, a ternary tetragonal scheelite structure tungstate with strontium and cerium cations, (Sr,Ce)WO4 , was synthesized. As much as 35% Ce could be inserted into the structure, leaving 1\over 7 of the (Sr,Ce) cation sites vacant. Partial ordering of Sr and Ce, with atomic displacements, were shown by high-resolution electron microscopy. Two-dimensional incommensurate modulations occur in this material, in small domains 20 nm in size. The band gap of this compound is significantly lower than the band gap of SrWO4 and this was related to the distortions of WO4 and (Sr,Ce)O8 polyhedra. The band gap value of 3.2 eV makes Sr1/2 Ce5/14 □1/7 WO4 a promising candidate for violet luminescence.