| Summary: | 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.
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