DFT and semi-empirical analyses of Cr-3(+) and Fe3+ impurity centers in Cs2NaYF6: Microscopic insight into structural properties

A detailed microscopic study of the local geometry was performed for the cation sites in fluoroelpasolite Cs2NaYF6 crystal doped with 3d ions (Cr3+ and Fe3+). Electronic structure of pure, Crdoped and Fe-doped Cs2NaYF6 has been studied by determining various properties: substitution energies of dopant ions, ionic Mulliken charges, atomic coordinates and unit cell parameters for the optimized structures. Also, the optimized local geometry of all three cation sites before and after the possible dopant ions substitutions has been deduced by DFT calculations. It is shown that the local symmetry of both Y3+ and Na+ sites maintains its cubic form after both Fe and Cr substitution; however, Fe ions lead quite larger distortion on ligand lengths at Y-site. The optimized structure has been used independently to calculate zero-field splitting parameters (ZFSPs) and crystal field parameters (CFPs) of both Cr3+ and Fe3+ centers. The calculated ZFSPs of Fe(3+ )ions indicate that the results predicted by SPM for both Y3+ site and Na+ site agree well with the previous experimental observations of ZFSPs. It can be inferred from the findings regarding both electronic structure and local optimized geometry that substitution of both Cr3+ and Fe3+ ions for Y3+ is more likely in C(s)2NaYF(6). (C) 2019 Elsevier Ltd. All rights reserved