On the correlation between optical and electrical properties in reduced lithium niobate crystals

The optical transmission of LiNbO 3 single crystals has been measured in the wavelength range 200-900 nm, for different degrees of reduction, to study the effect of reduction on the optical characteristics of LiNbO 3 near the fundamental absorption edge. The optical transitions in LiNbO 3 were found to be indirect and the band gap decreased with increasing degree of reduction. The band observed at 2.48 eV in the absorption spectrum in heavily reduced samples has been attributed to the formation of polarons and the theoretical model of Reik and Heese (1967) for small polarons is used to correlate the optical and electrical properties.