Synthesis and photoluminescence properties of a novel Sr₂Al₆O₁₁:Mn⁴⁺ red phosphor prepared with a B₂O₃ flux

A novel Mn⁴⁺-doped aluminate red phosphor Sr₂Al₆O₁₁:Mn⁴⁺ was synthesized by a solid-state reaction, and we investigated its photoluminescence properties. Sr₂Al₆O₁₁, which has a similar structure to Sr₄Al₁₄O₂₅, was formed as the main phase after heating alpha-alumina, strontium carbonate, manganese dioxide, and magnesium oxide with 2.5% B₂O₃ at 1000 °C for 12 h or more. The Sr₂Al₆O₁₁:Mn⁴⁺ phosphor exhibited red photoluminescence with peaks at around 652 and 665 nm, which arise from the spin-forbidden transition of the Mn⁴⁺ cation from the ²E to the ⁴A₂ state. The phosphor can be excited by near ultraviolet or blue LED light because it had a broad excitation band from the near-ultraviolet to the blue light region. The emission intensity was increased by co-doping with Mg²⁺ cations, which act as charge compensators. The amount of Mg required for the most effective charge compensation was 10 times the optimum Mn concentration. From these results, we confirmed that Sr₂Al₆O₁₁ could act as the host structure for Mn⁴⁺-doped phosphors.