Crystal structure, vibrational properties and luminescence of NaMg3Al(MoO4)5 crystal doped with Cr 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 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.