Understanding the defect levels and photoluminescence in a series of bismuth-doped perovskite oxides: First-principles study

First-principles calculations using the hybrid density functional are carried out to study the defect levels and photoluminescence of bismuth doped in perovskites RAlO₃ (R=Y, Gd, La) and LaBO₃ (B=Al, Ga, In). Bismuth dopants are confirmed to be predominantly Bi^3+ occupying the R site, i. e. , Biₑ^0 (R=Y, Gd, La). The variation of the electron trap depth Biₑ (0/-1) is shown mainly due to the shift of the conduction band, while the hole trap level Biₑ (+1/0) shows the correlation with the shortest R--O bond length in hosts. Based on the defect level diagram from the first-principles calculation, the transition types of excitation and emission are predicted. Among the systems considered, the lowest excited level that produces the photoluminescence is the ^3P₀, ₁ levels of the 6s^16p^1 configuration of Bi^3+, except for Bi^3+-doped LaAlO₃, which is the valence band to Bi^3+ charge transfer state. The photoluminescence involving ^3P₀, ₁ states shows similar Stokes shift in the series, and the excitation and emission energies exhibit almost linear correlation with the band gaps of hosts of a slope 0. 22. Furthermore, our calculations show that there is no tendency of forming excessive Bi^3+ pairs in all the five RBO₃: Bi^3+, while the Gd^3+-Gd^3+ coupling in GdAlO₃ provides a ``bridge'' for energy migration from an excited isolated Bi^3+ ion to the Bi^3+ pairs that are naturally present due to random distribution, leading to the 495-nm emission being observed uniquely in bismuth-doped GdAlO₃ among the series of systems considered. The results lay the basis for manipulating the trap levels and excitation and emission wavelengths in Bi^3+-doped perovskite oxides.