Optical Properties and Defects of Double Doped Crystals LiNbO3:Mg(5.05):Fe(0.009) and LiNbO3:Zn(4.34):Fe(0.02) (mol%)

Abstract

Photoinduced light scattering, laser conoscopy, and IR spectroscopy in the absorption region of OH stretching vibrations are used to study photorefractive properties and compositional homogeneity of double doped (mol%) LiNbO₃:Mg(5.05):Fe(0.009) and LiNbO₃:Zn(4.34):Fe(0.02) crystals grown from a congruent melt. All frequencies in the IR spectrum of the LiNbO₃:Mg(5.05):Fe(0.009) (mol%) crystal in the region of OH stretching vibrations are shifted to the high-frequency region compared with the spectrum of the nominally pure congruent crystal. This is caused by the absence of \(\rm{Nb}_{Li}^{4+}\) point defects and the corresponding (V_Li)–OH complex defects in the crystal structure and by the formation of new Mg_Li–Mg_Nb–OH and Mg_Li–OH–Fe_Nb complex defects. The LiNbO₃:Zn(4.34):Fe(0.02) (mol%) crystal (zinc concentration is between threshold concentrations for ∼3.0 mol% and 7.0 mol% of ZnO) is found to be much more compositionally homogeneous than the LiNbO₃:Mg(5.05):Fe(0.009) (mol%) crystal, despite much higher iron content in the former. This is explained by the fact that magnesium content in this crystal is close to the threshold concentration for ∼5.5 mol% of MgO. Neither of the crystals exhibits photoinduced light scattering.