First-principles study of electronic structure of Er-doped monoclinic ZrO₂

Abstract

The electronic structure of Er-doped monoclinic ZrO₂ was investigated by the generalized gradient approximation (GGA), GGA plus on-site Coulomb interaction (GGA + U) calculation, and modified Becke-Johnson (MBJ) exchange potential calculation. In the GGA calculation, the minimum bandgap energy of ZrO₂ was estimated to be 3.74 eV. The valence band was mainly composed of O 2p states, which strongly hybridized with the Zr 4d states. The conduction band was composed of Zr 4d and O 2p states. When an Er atom replaced one of the Zr atoms, seven-fold Er 4f states appeared in the forbidden gap of ZrO₂. Considering the spin–orbit coupling, the energy positions of the seven-fold Er 4f states in the forbidden gap hardly changed. Based on the GGA + U calculation, the Er 4f states shifted to the lower energy direction and entered into the valence band of ZrO₂ with an increase in the U parameter. In addition, the MBJ calculation gave similar results using a small U parameter in the valence band energy region, while the conduction band region is similar to the GGA + U calculation result with a large U parameter. Based on these results, we concluded that the GGA calculation is the most appropriate to describe the position of Er 4f states in the bandgap of Er-doped ZrO₂ phosphors among the three kinds of calculation methods examined in the present study.