Effects of Neighboring Polyhedron Competition on the 5d Level of Ce3+ in Lanthanide Garnets

Herein, we provide a direct explanation for the reverse garnet effect based on polyhedron competition. On multisite substitution, the deformation of the dodecahedron which will accommodate Ce3+ meets suppression from a neighboring octahedron and tetrahedron. This makes the dodecahedral deformation nonisotropic. Further, it is found that the lowest 5d state of Ce3+ in garnet is closely related to the tetragonal distortion of the dodecahedron, which is characterized by a simplified cuboid model. Crystal-field calculations reveal how the edge-ratio of the cuboid affects energy levels. This model gives a satisfactory explanation for the reverse garnet effect and is helpful for seeking novel garnet-based luminescent materials.