Local lattice distortion induced by substitution of Si for Ge in Li2CaGe1−xSixO4 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 Li2CaGe1−xSixO4 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 Li2CaGe1−xSixO4 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.