First-principles study of Bi3+ -related luminescence and traps in the perovskites CaMO3(M=Zr,Sn,Ti)

Abstract

The ${\mathrm{Bi}}^{3+}$ ion is an excellent activator and sensitizer for luminescent materials. However, the complexity and variety of the ${\mathrm{Bi}}^{3+}$-related transitions bring a great challenge to the study of luminescence processes of ${\mathrm{Bi}}^{3+}$ doped materials. Here, we presented first-principles calculations to determine the excitation, relaxation, and emission processes of ${\mathrm{Bi}}^{3+}$ activated materials by using $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}(M=\mathrm{Zr},\phantom{\rule{0.28em}{0ex}}\mathrm{Sn},\phantom{\rule{0.28em}{0ex}}\mathrm{Ti})$ as prototype systems, where ${\mathrm{Bi}}^{3+}$ substitutes ${\mathrm{Ca}}^{2+}$ in similar coordinate environments but presents tremendously different excitation and emission spectra. The equilibrium geometric structures of excited states were calculated based on density-functional theory (DFT), with appropriately constraining the electron occupation and including the spin-orbit couplings. Then the hybrid DFT calculations were carried out to obtain the electronic structures and defect levels. Different metastable excited states and Stokes shift were obtained for $M=\mathrm{Zr}$, Sn, and Ti, which explain the remarkable differences in the measured emission spectra. The energies of three types of transitions are obtained from the calculations, including intra-${\mathrm{Bi}}^{3+}$ bands transition and charge transfer between ${\mathrm{Bi}}^{3+}$ ions and the band edges. This leads to a clear and reliable interpretation of all the excitation spectra in the series. The method and its applications to $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}$ show the potential of first-principles calculations in analyzing and predicting luminescent properties of ${\mathrm{Bi}}^{3+}$ activated materials.