Exploration of the Electronic Structure of Monoclinic α-Eu2(MoO4)3: DFT-Based Study and X-ray Photoelectron Spectroscopy

The powder α-Eu2(MoO4)3 sample was prepared by the solid-state reaction method. The phase purity of the final powder product was verified by X-ray diffraction analysis. The constituent element core levels and valence band are measured by X-ray photoelectron spectroscopy as a function of Ar+ ion (2.5 keV, 7–8 μA/cm2) bombardment time. The formation of Mo5+ and Mo4+ states at high bombardment times was detected. The Eu–O and Mo–O bonding was considered in comparison with other Eu3+- and Mo6+-containing oxides using binding energy difference parameters. The transparency range obtained for the pure α-Eu2(MoO4)3 tablet is λ = 0.41–0.97 μm, as estimated at the transmission level of 5%. The short-wavelength cut edge in α-Eu2(MoO4)3 is governed by the direct allowed optical transitions within the band gap of Eg = 3.74 eV (300 K). The band structure of α-Eu2(MoO4)3 was calculated by ab initio methods and strongly different results were obtained for the spin up/down configurations. The Eu-4f states are located around 2.2 eV and −4.0 eV for spin up (↑) and the structures situated at around 6.5 and 5.5 eV for spin down (↓) configuration. The calculated spin magnetic moments are in excellent relation to the Slater-Pauling rule and within the Eu sphere the magnetic moment of 4f electrons is ∼5.99 μB.