Infrared Transmission Spectra of TiS3: Fundamental Absorption Edge, Phonons, and Excitons

Abstract

Transmission spectra of TiS₃ single crystal whiskers in the infrared and optical bands have been studied at various light polarizations in the temperature range from room to liquid helium. The absolute absorption coefficients have been determined. Previously unknown phonon modes have been observed in the far infrared region. The study of the temperature dependence of the band gap width \({{\mathcal{E}}_{{\text{g}}}}\) has shown that it increases by 50 meV under cooling from 300 to 5 K. The comparison of spectra measured at different polarization directions indicates that the optical gap is anisotropic. A 1.28-eV absorption peak has been detected below ~150 K and has been attributed to the excitation of excitons.