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 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 = 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.

Automated summary

The study used first-principles calculations to analyze the excitation, relaxation, and emission processes of Bi3+ activated materials, revealing significant differences in emission spectra due to the substitution of Bi3+ for Ca2+ in different coordination environments. Additionally, calculations provided insights into metastable excited states and Stokes shift for different materials, explaining the differences in measured emission spectra.