Microscopic insight into electronic and structural properties of Cr3+ and Fe3+ impurities in Cs2NaAlF6 via DFT and SPM analyses


Erbahar D., EMÜL Y. , Acikgoz M.

JOURNAL OF FLUORINE CHEMISTRY, cilt.226, 2019 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

Allowing high transition metal (TM) ions doping concentrations makes the fluoroelpasolite crystals Cs2NaMF6 (M = Al, Ga) quite interesting in various laser applications. In this study, we explored the influence of the dopant ions on the electronic and structural properties of Cs2NaAlF6. Particular attention is paid to the influence of trivalent TM ions (Cr3+ and Fe3+) on the local structure around the possible substitutional cation sites by investigating the optimized geometry around impurity sites due to Cr3+ and Fe3+ using density functional theory (DFT). The obtained structural data are utilized for the calculations of zero-field splitting (ZFS) parameters (ZFSPs) and crystal field parameters (CFPs) of both dopant ions independently in the frame of semi empirical superposition model (SPM). It is shown that remarkable change on the ZFSPs comes not from the distortion on metal-ligand distance but from that on the angular positions of the ligands around the impurity centers. It is dearly shown that the substitution of both Cr3+ and Fe3+ ions take place with significant influence on electronic structure and geometry for the trivalent Al3+ sites. The presented results here have significant potential to better understand the low-symmetry effects in especially optical applications of Cs2NaAlF6:Cr3+ and Cs2NaYF6:Fe3+ systems. Particularly, the calculated CFPs for Cs2NaYF6:Fe3+ system may serve as the only record in literature.