Structural and vibrational study of chromium doped elpasolite crystals Cs2NaAlF6

The influence of site-symmetry and electron phonon coupling in Cs2NaAlF6:Cr3+ is probed by correlation of optical and structural measurements. Based on neutron and x-ray analysis the structure is a distorted R3m¯, exhibiting a unique stacking interaction. Selection rules have been used to assign the Raman-active zone-center vibrations. Although local and bulk mode frequencies differ slightly, indicating that the guest Cr3+ ion does not significantly perturb the host structure, vibrational analysis indicates the Cr3+ ion is coupled to the first coordination sphere of the Al–F lattice.