Color and Constitution of CrVI-Doped Bi2O3 Phases: The Structure of Bi14CrO24

The structure of the deeply red chromium-doped Bi2O3 phase Bi14CrO24 is described: space group I4/m (Z=2); a=8.684 (1) ?, c=17.238 (1) ?. The BiIII polyhedra show distinct distortions due to steric lone-pair effects. There is definite spectroscopic evidence that chromium is present as CrVIO2-4 tetrahedra, which occupy rather large cages in the lattice. They are only weakly tied to the frame of BiIII cations––leading to distinct disorder phenomena. The red shift of the absorption edge with respect to the edge energies of the undoped Bi2O3 phases and the corresponding color effect are discussed as originating from a charge transfer process between BiIII and CrVI via interconnecting oxygen atoms.