Local lattice distortion induced by substitution of Si for Ge in Li₂CaGe_1−xSi_xO₄ solid solutions

Possible reasons for essential differences in values of the total crystal field splitting and centroid shift of Ce³⁺ 5d configuration for isostructural Li₂CaGeO₄ and Li₂CaSiO₄ were analyzed by means of X-ray diffraction method and luminescent spectroscopy. It was found that the increase in Si concentration in Ce³⁺-doped Li₂CaGe_1−xSi_xO₄ solid solutions leads to increasing of noncubic crystal field splitting parameter (∆) of the Ce³⁺ 5d configuration, indicating to an enhancement of distortion from the cubic symmetry of the calcium dodecahedral site upon going from Li₂CaGeO₄ to Li₂CaSiO₄. The results of X-ray diffraction analysis of Li₂CaGe_1−xSi_xO₄ show that the linear decrease of the unit-cell parameters with increasing Si-content is followed by complex changes in the geometry of the Ca polyhedra. Changes in the electronic structure with the composition of the solid solutions are also discussed. - Highlights: • The luminescence properties of Ce³⁺ ions in Li₂CaGe_1−xSi_xO₄ are analyzed. • The results of XRD analysis show changes in the geometry of the Ca polyhedra with the composition. • The increase in Si content leads to increasing of Ce³⁺ noncubic crystal field splitting parameter. • Local lattice distortion induced by substitution of Si for Ge as an explanation