Violation of axial symmetry of optical properties in the trigonal crystal Nd:GdFe2.1Ga0.9(BO3)4

Strong dependence of birefringence and absorption spectra of d-d, f-f and charge transfer transitions on the direction of light beam in the plane perpendicular to the threefold crystallographic axis has been found out in trigonal crystal Nd:GdFe2.1Ga0.9(BO3)4. X-ray measurements have shown that the crystal consists of inversion twins, whose formation is stimulated by the partial substitution of Fe by Ga. Observed violation of axial symmetry of the trigonal crystal optical properties is accounted for on the basis of assumption about stripe domain structure of the inversion twins.