Structure determination and a vibrational study for the hexagonal elpasolite Cs₂NaGaF₆:Cr³⁺

Single crystals of 0.5% Cr³⁺-doped Cs₂NaGaF₆ were studied by means of x-ray diffraction and polarized Raman scattering. The crystal exhibits a unique stacking interaction, with a hexagonal structure with Rm symmetry. Polarized Raman spectra recorded at 16 and 300 K reveal sidebands that are ascribed to the local vibrational of the [CrF₆] coordination unit, which differ markedly from those of the Cs₂NaGaF₆ host lattice. The results are compared to findings for other elpasolite lattices, and the room temperature luminescence quantum yields are discussed in terms of a delicate balance between electron–phonon strength and lattice distortion.