We report the measurements of the pseudodielectric function, far-infrared reflectivity and Raman scattering spectra in Sr 14 Cu 24 O 41 single crystal. We study the lattice and the spin dynamics of the Cu 2 O 3 spin ladders and CuO 2 chains of this compound. The ellipsometric and the optical reflectivity measurements yield the gap values of 1.4 eV, 1.86 eV, 2.34 eV (2.5 eV) for the ladders (chains) along the c-axis and 2.4 eV along the a-axis. The electronic structure of the Cu 2 O 3 ladders is analyzed using tight-binding approach for the correlated electron systems. The correlation gap value of 1.4 eV is calculated with the transfer energy (hopping) parameters t = t 0 =0.26 eV, along and perpendicular to legs, t xy =0.026 eV (interladder hopping) and U=2.1 eV, as a Coulomb repulsion. The optical parameters of the infrared active phonons and plasmons are obtained by oscillator fitting procedure of the reflectivity spectra. Raman scattering spectra are measured at different temperatures using different laser line energies. The two-magnon peak is observed at about 2880 cm −1 . At temperatures below 150 K the new infrared and Raman modes appear due to the charge ordering.

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We measured the room temperature far-infrared reflectivity and Raman scattering spectra of single crystals. The frequencies of infrared active modes are obtained by Kramers - Kronig analysis of reflectivity data. The assignation of the observed modes is given according to the lattice dynamical calculation based on the valence shell model. According to the factor group analysis of the space group, which assumes the existence of the and chains, the 15 and 7 modes can be expected in both ir and Raman scattering spectra from the (001) plane. Only eight Raman and six infrared modes of symmetry are clearly seen. In the case of symmetry, three modes are observed both in the Raman and in the ir reflectivity spectra. The frequencies of these ir and Raman modes differ significantly. Because of this, we concluded that the space group of the crystal structure cannot be (non-centrosymmetric), but the space group which includes the mutual exclusion between Raman and infrared activity (centrosymmetric space group). We have shown that the appropriate space group is Pmmn, for which we found our experimental spectra in complete agreement with factor-group analysis. This means that V atoms are indistinguishable in the unit cell and in a mixed-valence state.

The optical properties of sodium-deficient α ′ -NaxV2O5 (0.85 ≤ x ≤ 1.00) single crystals are analyzed in the wide energy range, from 0.012 to 4.5 eV, using ellipsometry, infrared reflectivity, and Raman scattering techniques. The material remains insulating up to the maximal achieved hole concentration of about 15 %. In sodium deficient samples the optical absorption peak associated to the fundamental electronic gap develops at ∼ 0.44 eV. It corresponds to the transition between vanadium dxy and the impurity band, which forms in the middle of the pure α ′ -NaV2O5 gap. Raman spectra measured with incident photon energy larger then 2 eV show strong resonant behavior, due to the presence of the hole-doping activated optical transitions, peaked at ∼ 2.8 eV.