Photoluminescence Spectra Correlations with Structural Distortion in Eu³⁺- and Ce³⁺-Doped Y₃Al_5-2(Mg,Ge)O₁₂ (x = 0,...

Garnet-type materials consisting of Y₃Al_5-2(Mg,Ge)O₁₂ (x = 0, 1, 2), combined with Eu³⁺ or Ce³⁺ activator ions, were prepared by a solid-state method to determine the structural and optical correlations. The structure of Y₃Al_5-2(Mg,Ge)O₁₂ (x = 1, 2) was determined to be a cubic unit cell (Ia-3d), which contains an 8-coordinated Y³⁺ site with octahedral (Mg,Al)O₆ and tetrahedral (Al,Ge)O₄ polyhedra, using synchrotron powder X-ray diffraction. When Eu³⁺ or Ce³⁺ ions were substituted for the Y³⁺ site in the Y₃Al_5-2(Mg,Ge)O₁₂ host lattices, the emission spectra showed a decrease in the magnetic dipole f-f Eu³⁺ transition and a redshift of the d-f Ce³⁺ transition, related to centrosymmetry and crystal field splitting, respectively. These changes were monitored according to the increase in Mg²⁺ and Ge⁴⁺ contents. The dodecahedral and octahedral edge sharing was identified as a key distortion factor for the structure-correlated luminescence in the Eu³⁺/Ce³⁺-doped Y₃Al_5-2(Mg,Ge)O₁₂ garnet phosphors.