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

Abstract

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 4G5/2 → 6H9/2 band is dominating in the BaSm2(MoO4)4 luminescence.