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 $({\mathrm{Bi}}^{1+})$ ions can replace alkaline metal ions in pollucite ${\mathrm{CsAlSi}}_{2}{\mathrm{O}}_{6}$, leucite ${\mathrm{KAlSi}}_{2}{\mathrm{O}}_{6}$, and ${\mathrm{CsGaGe}}_{2}{\mathrm{O}}_{6}$, forming ${(\text{BiO})}^{\ensuremath{-}}$ complexes with a ligand oxygen ion, producing photoluminescence with photon energy around $1\phantom{\rule{0.16em}{0ex}}\text{eV}$ with sub-ms decay time. The emission energy is predicted to decrease as the ${(\text{BiO})}^{\ensuremath{-}}$ bond length decreases, manifesting the ligand-field effect. In ${\mathrm{BaZrO}}_{3}$ and ${\mathrm{SrZrO}}_{3}$, under a sufficiently strong reducing atmosphere, Bi dopants can replace ${\mathrm{Ba}}^{2+}$ or ${\mathrm{Sr}}^{2+}$ ions as ${\mathrm{Bi}}^{1+}$ 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 ${\mathrm{BaZrO}}_{3}$ and ${\mathrm{SrZrO}}_{3}$ 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 ${\mathrm{Bi}}^{1+}$ substitution for large alkaline or alkaline earth ions, and offers a guideline for understanding the phenomena in similar systems.