Structure and redshift of Ce3+ emission in anisotropically expanded garnet phosphor MgY2Al4SiO12:Ce3+

Abstract

To achieve a redshift of the Ce³⁺ emission, an overall compression of a garnet phosphor with anisotropic expansion of the local environment for the activator ion Ce³⁺ was designed, by the strategy of incorporating the small cation Mg²⁺ into the dodecahedral Y³⁺ site. The successful substitution of Mg²⁺ in the dodecahedral Y³⁺ site in the novel garnet phosphor MgY₂Al₄SiO₁₂:Ce³⁺ was confirmed by the Rietveld refinements of XRD data, TEM and XPS results. The emission of MgY_1.94Al₄SiO₁₂:0.06Ce³⁺ ranges from 500 nm to 750 nm with the maximum being at 568 nm, which means that the expected redshift is realized, comparing with the commercial phosphor YAG:Ce³⁺. Furthermore, an anisotropic expansion mechanism, with a comprehensive view of crystal field splitting and the dynamic aspect factor of the Stokes shift, was proposed to interpret such a redshift, based on the bond length variation and the crystal field splitting data versus those of the counter phosphor Y₃Al₃MgSiO₁₂:Ce³⁺ and YAG:Ce³⁺. The anisotropic expansion from cation substitution could serve as a general strategy to design new phosphors for high colour rendering index white LED lamps.