Investigation Investigation on crystal structures, optical properties, and band structure calculations of In2-xMxTeO6 (M = Ga, Bi, La)

The study of structure, optical properties, and band structure of M substituted-In2TeO6 (M = Ga3+, Bi3+, and La3+) is presented. Solubility limit of each cation is different varying from 10% for La3+ to 20% for Ga3+ and 25% for Bi3+. Both XANES and XPS confirm the oxidation states of Bi3+ and Te6+. Crystallographic data of bond lengths and bond angles suggest no significant distortion of M-O6 octahedra for all samples; however, the stereoactive 6s(2) lone-pair electrons in Bi cause In/Bi cation in In/Bi-O-6 to shift toward one edge of the octahedra. The band structure calculation was useful to clarify that the fundamental band gap energies of all series originate from the direct allowed transition. Interestingly, Bi greatly influences the conduction band dispersion and Bi 6s state additionally contributes at the valence band maximum, while the valence band of other M-doped and un-doped samples are mainly O 2p and In 4d in character. All compounds similarly exhibit photoluminescence properties. The strong PL peak mainly originated from the near band edge transition and the broad peak from Te6+-O charge transfer are observed in all samples. (C) 2017 Elsevier B.V. All rights reserved.