Rationalization of near-infrared luminescence of bismuth ions in mixed oxides

Bismuth-activated materials with broadband luminescence have continued to attract interest for their potential applications in phosphors and broadband optical amplifiers. This study aims to elucidate the near-infrared (NIR) luminescence observed in different oxides via first-principles predictions on the formation energies of intrinsic defects and bismuth dopants, as well as the optical transition processes. The results show that monovalent Bi (Bi¹⁺) ions can replace alkaline metal ions in pollucite CsAlSi₂O₆, leucite KAlSi₂O₆, and CsGaGe₂O₆, forming (BiO)^- complexes with a ligand oxygen ion, producing photoluminescence with photon energy around 10.16em0exeV with sub-ms decay time. The emission energy is predicted to decrease as the (BiO)^- bond length decreases, manifesting the ligand-field effect. In BaZrO₃ and SrZrO₃, under a sufficiently strong reducing atmosphere, Bi dopants can replace Ba²⁺ or Sr²⁺ ions as Bi¹⁺ ions, producing the observed emission around 1000 nm with a sub-ms decay time. The shorter wavelengths are due to the weaker ligand field in BaZrO₃ and SrZrO₃ than in pollucite and leucite. This study provides a rational interpretation for the NIR luminescence of sub-ms decay time in the Bi-doped mixed oxides, attributing it to the emission of Bi¹⁺ substitution for large alkaline or alkaline earth ions, and offers a guideline for understanding the phenomena in similar systems.