Optical Properties and Electronic Structure of the Misfit Layer Compounds 'lnnb2x5' (ln Identical to Y, La or Nd; X Identical to S or Se)

We have determined the reflectance of the misfit layer compounds 'LnNb2X5' (Ln identical to Y, Nd or La; X identical to S or Se) between 50 meV and 6 eV for the electric field parallel to the layers. By fitting a Lorentz-Drude model the spectral distribution of the components of the energy loss function and of the conductivity function parallel to the layers were obtained. On the assumption of a charge transfer from the mod LnX mod to the mod NbX2 mod layers the values of the effective mass could be calculated from the intraband contribution to the optical spectra.