Crystal structure, vibrational properties and luminescence of NaMg3Al(MoO4)5 crystal doped with Cr3+ ions

Crystals of NaMg3Al(MoO4)5 doped with 0.5% Cr3+ ions have been synthesized and characterized by a single-crystal X-ray structure analysis and IR, Raman, electron absorption and luminescence spectroscopic studies. It has been shown that NaMg3Al(MoO4)5 crystallizes in the P1¯ structure, with a=6.8744(8) Å, b=6.9342(7) Å, c=17.605(2) Å, α=87.788(8)°, β=87.727(9)°, γ=78.501(9)°, Z=2. The characteristic feature of the structure is its enormously large thermal displacement parameter for sodium, even at 105 K. The IR and Raman spectra indicate significant interactions between the MoO42− ions in the structure. The electron absorption, excitation and luminescence studies have shown that there are at least two different sites of incorporated Cr3+ ions in the NaMg3Al(MoO4)5 crystal structure. They differ themselves by strength of crystalline field. One of them is characterized by Cr3+ in low ligand field and 4T2→4A2 emission whereas the second is characterized by higher strength of the crystal field and dominant 2E→4A2 emission. Temperature-dependent studies show that the compound does not exhibit any phase transition.

Graphical abstractCrystal structure of NaMg3Al(MoO4)5. The splitting of sodium position into four contributors in the cavity formed by Mo tetrahedra and Mg octahedra is shown.Figure optionsDownload full-size imageDownload as PowerPoint slide