Band gaps and electronic structure of alkaline-earth and post-transition-metal oxides

The electronic structure in alkaline-earth AeO (Ae=Be, Mg, Ca, Sr, Ba) and post-transition-metal oxides MeO (Me=Zn, Cd, Hg) is probed with oxygen K-edge x-ray absorption and emission spectroscopy. The experimental data are compared with density-functional theory electronic-structure calculations. We use our experimental spectra of the oxygen K edge to estimate the band gaps of these materials and compare our results to the range of values available in the literature. From the calculated partial density of states we conclude that the position of main O K-edge x-ray emission feature in BeO, SrO, and BaO is defined by the position of the $np$ states of the cation while in the other oxides studied here the main O K-edge x-ray emission feature is defined by the position of the (n-1)d (for CaO) or $nd$ states of the cation.