Exciton transition and electronic structure of PbMoO4 crystals studied by polarized light

Published in Physica status solidi. B, Basic solid state physics, Vol. 247, No. 2, pp405-410, 2010.Polarized reflectivity spectra of PbMoO4 crystals have been measured using synchrotron radiation up to 20 eV. The optical constants for the crystallographic axes are derived by using a Kramers-Kronig analysis. It is found that the exciton band at 3.6 eV shows a doublet structure with distinct dichroism. X-ray photoemission spectroscopy (XPS) and the calculation of the elec-tronic structure by a discrete variational Xα method are also carried out. The calculation shows that the va-lence band and the conduction band are mainly com-posed of the O 2p and Mo 4d states, respectively, and the Pb state contributes appreciably to the top of the valence band and the bottom of the conduction band. The valence-band XPS spectrum of PbMoO4 is com-pared with that of PbWO4, which reveals a remarkable difference between them. This difference reflects dif-ferent magnitude of hybridization of Mo 4d or W 5d state to the valence band. The exciton transition is ex-plained in terms of the cationic Pb 6s → 6p excitation model taking into account the crystal-field splitting and the spin-orbit interaction of Pb 6p state. From a comparison of the doublet structure of the exciton band of PbMoO4 and PbWO4, it is suggested that the electron-hole exchange interaction plays an important role for the exciton transitions in both materials.