Search for: All records

Comparison of the optical properties of Co₃O₄and ZnCo₂O₄elucidates fundamental differences in mechanisms of photoinduced polaron formation based on the presence or absence of substitutional lattice defects arising from cation inversion. 

Polaron formation following optical absorption is a key process that defines the photophysical properties of many semiconducting transition metal oxides, which comprise an important class of materials with potential optoelectronic and photocatalytic applications. In this work, we use hematite (α-Fe 2 O 3 ) as a model transition metal oxide semiconductor to demonstrate the feasibility of direct optical population of band edge polaronic states. We employ first-principles electron–phonon computations within the framework of the density functional theory+ U+ J method to reveal the presence of these states within a thermal distribution of phonon displacements and model their evolution with temperature. Our computations reproduce the temperature dependence of the optical dielectric function of hematite with remarkable accuracy and indicate that the band edge optical absorption and second-order resonance Raman spectra arise from polaronic optical transitions involving coupling to longitudinal optical phonons with energies greater than 50 meV. Additionally, we find that the resulting polaron comprises an electron localized to two adjacent Fe atoms with distortions that lie primarily along the coordinates of phonons with energies of 31 and 81 meV.