Structural Evolution and Effect of the Neighboring Cation on the Photoluminescence of Sr(LiAl3)1-x(SiMg3)xN4:Eu2+ Phosphors

In this study, a series of Sr(LiAl3)(1-x)(SiMg3)(x)N-4:Eu2+ (SLA-SSM) phosphors were synthesized by a solid-solution process. The emission peak maxima of SLA-SSM range from 615nm to 680nm, which indicates structural differences in these materials. Li-7 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 Eu2+ concentration in SLA-SSM is much higher than that in in SrLiAl3N4:Eu2+ and SrSiMg3N4:Eu2+ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation.