Bi³⁺-Related Multimode Emission in Garnet: A First-Principles Study

In this work, systematic first-principles calculations were performed to investigate the multiband emissions of Bi-doped Y₃Ga(Al)₅O₁₂ phosphors. The predicted emissions of Bi³⁺ show that the violet narrow-band emission can be attributed to the ³P₁-¹S₀ transition of Bi³⁺ at Y sites, and both the metal-to-metal charge transfer (MMCT) of Bi³⁺ at Ga (Al) sites and the luminescence of Bi³⁺ dimers can generate visible emissions. Detailed formation energy calculations subsequently rule out the possibility that the visible emission originates from the MMCT of Bi³⁺ at Ga (Al), as the concentration of Bi_Y is much greater than that of B_Ga (or Bi_Al). To better understand the relationship between the nephelauxetic effect and the coordination environment, the vacuum-referred binding energy (VRBE) model was utilized to determine the energy levels of bismuth ions relative to the vacuum level in different systems and at different sites. The results provide insight into the relationship between the coordination environment and the emission properties of Bi³⁺ and are helpful for analyzing and optimizing the luminescent properties of bismuth-doped garnet-like materials.