Electronic structures and nature of host excitation in borates

We report the electronic structures of three large band gap berates beta-BaB2O4, YBO3 and LuBO3, and corresponding binary oxides BaO, Y2O3, Lu2O3 and B2O3. The main objective of this investigation is to explore how the electronic structures of complex oxides relates to their binary oxides, and how tightly bound anionic groups lead to large gap oxides. The calculated electronic structures lead to good agreement between observed optical gap and structure of the valence band for these oxides. While the orates lead to large gap materials, the excitations across the band gap do not always involve bonding and antibonding states of berate groups that are common to all the ternary oxides considered in this work. Although the top of the valence band is characterized by hybridized O 2p- and B 2p-like states, the bottom of the conduction band can be due to metallic states. The presence of such stales near the bottom of the conduction band was speculated earlier from the excitation properties of YBO3. We have also explored the possibility of designing a multiphoton phosphor through core valence luminescence from a ternary oxide of Ba.