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

The Bi³⁺ ion is an excellent activator and sensitizer for luminescent materials. However, the complexity and variety of the Bi³⁺ -related transitions bring a great challenge to the study of luminescence processes of Bi³⁺ doped materials. Here, we presented first-principles calculations to determine the excitation, relaxation, and emission processes of Bi³⁺ activated materials by using CaMO₃: Bi³⁺ (M = Zr, Sn, Ti) as prototype systems, where Bi³⁺ substitutes Ca²⁺ 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 = 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- Bi³⁺ bands transition and charge transfer between Bi³⁺ 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 CaMO₃: Bi³⁺ show the potential of first-principles calculations in analyzing and predicting luminescent properties of Bi³⁺ activated materials. Copyright © 2021 American Physical Society.