Influence of Co³⁺ spin-state on optical properties of LaCoO₃ and HoCoO₃

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Optical properties of the isoelectronic compounds LaCoO₃ and HoCoO₃ has been experimentally and theoretically investigated. We've measured the real ε₁(ω) and imaginary ε₂(ω) parts of the dielectric function, reflectance R(ω) and optical conductivity at room temperature. The shift of the most pronounced spectral features to the high energy region on 0.3 eV associated with larger distortions due to the smaller rare earth ionic radii in HoCoO₃ in comparison with LaCoO₃ was observed. Also there was found an enhancement of absorption intensity in the range 1.3-2.3 eV in all kinds of spectra in HoCoO₃, which can be attributed basing on the results of LDA+U calculations to the different spin-states of Co³⁺ ion in these compounds. The shift of the onset of the absorption from less than 0.1 eV in LaCoO₃ to 0.7 eV in HoCoO₃ and an absorption intensity enhancement in a narrow spectral range 1.2-2.6 eV in HoCoO₃ are clearly seen from the calculated convolution of partial densities of states obtained in the LDA+U approach. Such changes are assumed to be induced by the different Co³⁺ spin-state in these compounds at room temperature.