Optical spectra of lithium niobate

The specific features revealed in the optical spectra of lithium niobate crystals at temperatures of 90 and 120–125°C can be attributed to the change in the electronic subsystem and the related isostructural transformation of the crystal lattice. In the near-IR range, the optical absorption spectra of lithium niobate crystals exhibit bands (1.43 eV) assigned to polarons of large radius with a binding energy of 0.48 eV. The decrease observed in the absorption coefficient at the maxima of these bands with an increase in the temperature to 160°C can be explained by the decay of polarons of large radius at these temperatures.