Analysis of the structure and abnormal photoluminescence of a red-emitting LiMgBO:Mn phosphor.

Mn is attracting increasing attention due to its potential application as an activated ion in the phosphors. In this study, a rare-earth free phosphor, LiMgBO:Mn, was synthesized using a high temperature solid-state reaction. Combined with X-ray diffraction and PL/PLE as well as first-principles calculation, the coordination environment of Mn was disclosed, revealing that Mn ions were inclined to occupy two partially filled Li sites. Under 427 nm-excitation, an abnormal deep red emission band centered at 705 nm was observed. This was due to the strong crystal field environment of Mn induced by the extremely distorted five-coordinated sites, which was proved by the electronic band structure obtained from the density functional theory calculations. In addition, the luminescence intensity and thermal stability of LiMgBO:Mn was significantly enhanced when Li was replaced by Na and K. This study disclosed the origin of the abnormal luminescence of Mn in LiMgBO and further enriched our understanding of the abnormal luminescence of Mn in special crystal structures (five-coordinated configuration).