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 $\left({\mathrm{Bi}}^{1+}\right)$ ions can replace alkaline metal ions in pollucite ${\mathrm{CsAlSi}}_2{O}_6$, leucite ${\mathrm{KAlSi}}_2{O}_6$, and ${\mathrm{CsGaGe}}_2{O}_6$, forming ${\left(\text{BiO}\right)}^{-}$ complexes with a ligand oxygen ion, producing photoluminescence with photon energy around $1\text{eV}$ with sub-ms decay time. The emission energy is predicted to decrease as the ${\left(\text{BiO}\right)}^{-}$ 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.