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

Abstract

First-principles calculations using the hybrid density functional are carried out to study the defect levels and photoluminescence of bismuth doped in perovskites $R{\mathrm{AlO}}_{3}$ ($R=\mathrm{Y}$, Gd, La) and $\mathrm{La}B{\mathrm{O}}_{3}$ ($B=\mathrm{Al}$, Ga, In). Bismuth dopants are confirmed to be predominantly ${\mathrm{Bi}}^{3+}$ occupying the $R$ site, i.e., ${\mathrm{Bi}}_{R}^{0}$ ($R=\mathrm{Y}$, Gd, La). The variation of the electron trap depth ${\mathrm{Bi}}_{R}(0/\ensuremath{-}1)$ is shown mainly due to the shift of the conduction band, while the hole trap level ${\mathrm{Bi}}_{R}(+1/0)$ shows the correlation with the shortest $R\text{--}\mathrm{O}$ 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 $^{3}P_{0,1}$ levels of the $6{s}^{1}6{p}^{1}$ configuration of ${\mathrm{Bi}}^{3+}$, except for ${\mathrm{Bi}}^{3+}$-doped ${\mathrm{LaAlO}}_{3}$, which is the valence band to ${\mathrm{Bi}}^{3+}$ charge transfer state. The photoluminescence involving $^{3}P_{0,1}$ 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 $\ensuremath{\sim}0.22$. Furthermore, our calculations show that there is no tendency of forming excessive ${\mathrm{Bi}}^{3+}$ pairs in all the five $RB{\mathrm{O}}_{3}$:${\mathrm{Bi}}^{3+}$, while the ${\mathrm{Gd}}^{3+}\text{\ensuremath{-}}{\mathrm{Gd}}^{3+}$ coupling in ${\mathrm{GdAlO}}_{3}$ provides a ``bridge'' for energy migration from an excited isolated ${\mathrm{Bi}}^{3+}$ ion to the ${\mathrm{Bi}}^{3+}$ pairs that are naturally present due to random distribution, leading to the 495-nm emission being observed uniquely in bismuth-doped ${\mathrm{GdAlO}}_{3}$ among the series of systems considered. The results lay the basis for manipulating the trap levels and excitation and emission wavelengths in ${\mathrm{Bi}}^{3+}$-doped perovskite oxides.