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

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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 Bi³⁺ occupying the R site, i.e., BiR⁰ (R=Y, Gd, La). The variation of the electron trap depth BiR(0/-1) is shown mainly due to the shift of the conduction band, while the hole trap level BiR(+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 6s¹6p¹ configuration of Bi³⁺, except for Bi³⁺-doped LaAlO₃, which is the valence band to Bi³⁺ 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 Bi³⁺ pairs in all the five RBO₃:Bi³⁺, while the Gd³⁺-Gd³⁺ coupling in GdAlO₃ provides a ``bridge'' for energy migration from an excited isolated Bi³⁺ ion to the Bi³⁺ 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 Bi³⁺-doped perovskite oxides.