Structural and spectroscopic properties of self-activated monoclinic molybdate BaSm2(MoO4)(4)

The crystal structure of new monoclinic molybdate BaSm₂(MoO₄)₄ is refined in monoclinic unit cell C2/m with cell parameters a = 5.29448 Å, b = 12.7232 Å, c = 19.3907 Å, β = 91.2812°, V = 1305.89 Å³. The crystal structure consists of the SmO₈ square antiprism joined with each other by the edges forming a 2D layer perpendicular to the c-axis. MoO₄ tetrahedra join SmO₈ by nodes and also participate in layer formation, and Ba ions are located between these layers. The lattice dynamics is theoretically calculated on the base of the crystal structure data. The Raman spectra are recorded and analyzed in comparison with theoretical calculations. The discrepancy between the experimental and calculated Raman frequencies does not exceed 2 cm⁻¹ for the most of Raman lines. The luminescence spectra of Sm³⁺ ions, which are positioned in the lowest local symmetry site C₁, strongly differ from those detected for another molybdate crystal, β-RbSm(MoO₄)₂, with the C₂ local symmetry. The ⁴G_5/2 → ⁶H_9/2 band is dominating in the BaSm₂(MoO₄)₄ luminescence.