Analysis of the structure and abnormal photoluminescence of a red-emitting LiMgBO3:Mn2+ phosphor

Abstract

Mn²⁺ is attracting increasing attention due to its potential application as an activated ion in the phosphors. In this study, a rare-earth free phosphor, LiMgBO₃:Mn²⁺, 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 Mn²⁺ was disclosed, revealing that Mn²⁺ 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 Mn²⁺ 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 LiMgBO₃:Mn²⁺ was significantly enhanced when Li⁺ was replaced by Na⁺ and K⁺. This study disclosed the origin of the abnormal luminescence of Mn²⁺ in LiMgBO₃ and further enriched our understanding of the abnormal luminescence of Mn²⁺ in special crystal structures (five-coordinated configuration).