Influence of co-doping of divalent ions on the photoluminescence intensity of Mn⁴⁺ doped CaAl₁₂O₁₉

Influence of co-dopings of divalent ions such as Mg²⁺, Zn²⁺, Cd²⁺ and Sr²⁺ ions in Mn⁴⁺-doped CaAl₁₂O₁₉ red phosphor on its photoluminescence characteristics has been investigated. Samples of Mn⁴⁺-doped CaAl₁₂O₁₉ and co-doped with Mg²⁺, Zn²⁺, Cd²⁺ and Sr²⁺ ions were synthesized by a solid-state reaction method. Significant enhancement of photoluminescence intensity was observed, when Mg²⁺ and Zn²⁺ were co-doped in Mn⁴⁺-doped CaAl₁₂O₁₉, while only slight enhancement was seen with Cd²⁺ and Sr²⁺ co-dopings. To investigate these differences in photoluminescence enhancement, change in local environment of Mn⁴⁺ ions due to co-dopings of divalent ions was examined by electron spin resonance (ESR) measurements and first principles calculations within a density functional theory. From these experimental and theoretical analysis, it has been confirmed that the local environment of Mn⁴⁺ changes significantly with Mg²⁺ and Zn²⁺ co-dopings, while Cd²⁺ and Sr²⁺ alter minimally the local environment of Mn⁴⁺ due to different substitution site.