Electronic structure of β-RbSm(MoO4)2 and chemical bonding in molybdates

Microcrystals of orthorhombic rubidium samarium molybdate, beta-RbSm(MoO4)(2), have been fabricated by solid state synthesis at T = 450 degrees C, 70 h, and at T = 600 degrees C, 150 h. The crystal structure has been refined by the Rietveld method in space group Pbcn with cell parameters a = 5.0984(2), b = 18.9742(6) and c = 8.0449(3) angstrom (R-B = 1.72%). Thermal properties of beta-RbSm(MoO4)(2) were traced by DSC over the temperature range of T = 20-965 degrees C, and the earlier reported beta <-> alpha phase transition at T similar to 860-910 degrees C was not verified. The electronic structure of beta-RbSm(MoO4) 2 was studied by employing theoretical calculations and X-ray photoelectron spectroscopy. It has been established that the O 2p-like states contribute mainly to the upper part of the valence band and occupy the valence band maximum, whereas the Mo 4d-like states contribute mainly to the lower part of the valence band. Chemical bonding effects have been analysed from the element core level binding energy data. In addition, it was found that the luminescence spectrum of beta-RbSm(MoO4)(2) is rather peculiar among the Sm3+ containing materials. The optical refractive index dispersion in beta-RbSm(MoO4)(2) was also predicted by the first-principles calculations.