COLOR, LUMINESCENCE AND BONDING PROPERTIES OF TETRAHEDRALLY COORDINATED CHROMIUM(IV), MANGANESE(V) AND IRON(VI) IN VARIOUS OXIDE CERAMICS

The spectroscopic properties (absorption, luminescence, EPR) of d(2)-c onfigurated cations (Fe(VI), Mn(V), Cr(VI)) doped into the tetrahedral sites of a great variety of oxidic solids are reviewed and supplement ed by new results. Angular overlap model calculations on the basis of the host site geometry, utilising a modified ligand field theory with different Racah parameters for e and t(2) orbitals, have been performe d, which nicely fit the experimental data. In particular, they give ev idence, that - in the case of Cr(IV) - the (1)E state is usually posit ioned well above the luminescing triplet state, in agreement with the experiment. Further, the calculations allow a characterization of the transition-metal-oxygen bond. It is finally shown, that the doping cat ion does not necessarily adopt the host site geometry; geometric crite ria are given.