The Family of Ln2Ti2S2O5 Compounds (Ln=Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y): Optical Properties

The optical properties of Ln₂Ti₂S₂O₅ compounds (Ln=Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y) have been measured. Diffuse reflectance spectra revealed a strong absorption band above 2 eV, which explains the color of the compounds. Moreover, other bands, with a lower intensity, have been attributed to 4f-4f rare earth transitions. In the case of neodymium the derived energy level scheme is rich enough to determinate a set of phenomenological crystal field parameters that correctly reproduce the spectrum. These parameters were also calculated from the crystallographic structure, in a good agreement with the experiment. Finally, the paramagnetic susceptibility, well reproduced by the calculation, confirms that the rare earth is in a trivalent state.