Structural Evolution and Effect of the Neighboring Cation on the Photoluminescence of Sr(LiAl 3 ) 1-x (SiMg 3 ) x N 4 :Eu 2+ Phosphors.

In this study, a series of Sr(LiAl ₃ ) _1-x (SiMg ₃ ) _x N ₄ :Eu ²⁺ (SLA-SSM) phosphors were synthesized by a solid-solution process. The emission peak maxima of SLA-SSM range from 615 nm to 680 nm, which indicates structural differences in these materials. ⁷ Li solid-state NMR spectroscopy was utilized to distinguish between the Li(1)N ₄ and Li(2)N ₄ tetrahedra in SLA-SSM. Differences in the coordination environments of the two Sr sites were found which explain the unexpected luminescent properties. Three discernible morphologies were detected by scanning electron microscopy. Temperature-dependent photoluminescence and decay times were used to understand the diverse environments of europium ions in the two strontium sites Sr1 and Sr2, which also support the NMR analysis. Moreover, X-ray absorption near-edge structure studies reveal that the Eu ²⁺ concentration in SLA-SSM is much higher than that in in SrLiAl ₃ N ₄ :Eu ²⁺ and SrSiMg ₃ N ₄ :Eu ²⁺ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation.
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