The optical gap of NiO

Abstract

The nature of the optical absorption gap in NiO at 4.0 eV is investigated. It is found that this gap is due to a band to band transition, where an electron is taken out of the valence band and placed into the conduction band. The optical gap of 6.0 eV found in Ni∶MgO is of a nature, where an electron is taken out of the oxygen 2p band and placed into the first affinity level of the Ni²⁺ ion (3d ⁸L»3d ⁹L⁻¹). The impurity band created in Ni_1−x Li _x O by the Li ions is found 2.3 eV below the bottom of the conduction band in agreement with model predictions.