Structural perfection of gadolinium gallium garnet (GGG; Gd(3)Ga(5)O(12)) epitaxial layers with incorporated divalent Co ions has been studied by means of high resolution X-ray diffraction, X-ray topography, transmission electron microscopy and optical spectroscopy. Epitaxial layers were grown by liquid phase epitaxy from super-cooled high temperature solution with different concentration of Co(3)O(4) and GeO(2) on both sides of the polished < 111 > oriented GGG substrates. In order to facilitate incorporation of Co(2+) ions into the garnet lattice optically inert Ge(4+) ions have to be introduced first. High structural perfection is a prerequisite to obtain absorption spectra required for the use GGG epitaxial layers as tunable infrared absorbers. (C) 2010 Elsevier B.V. All rights reserved.