Optical spectra of lithium tantalate

The optical spectra of lithium tantalate in the ferroelectric phase are investigated in the visible and near-IR ranges. Specific features in the optical spectra of lithium tantalate at temperatures of 120 and 180°C, namely, minima in the parameter σ of the Urbach rule and the degree of polarization of the luminescence band, indicate a rearrangement of the electronic subsystem and the corresponding isostructural transformations of the crystal lattice. In the near-IR range, the optical spectra contain bands at energies of 1.51, 1.30, and 1.75 eV, which, according to the shape and temperature behavior, are attributed to polarons of large radius with binding energies of 0.36, 0.31, and 0.42 eV, respectively.