The Yb₃Al₅O₁₂:Er crystals are interesting as promising material for lasers generating efficient emission in the near infrared range, working due to the upconversion mechanism. The trivalent erbium ion provide 2.94 mm line very useful for medical application and 1.55 mm for light guide communication. Due to the presence Yb³⁺ the metastable levels of Er³⁺ can be very effectively excited even by the radiation of much longer wavelengths. Yb₃Al₅O₁₂ (YbAG) is of cubic symmetry and belongs to the space group Ia3d. It is isostructural with frequently used yttrium aluminum garnet with a lattice parameter 1% greater. In the laser applications a structural quality of the crystal is of great importance.

The presently investigated crystal with 0%, 1.5 at.%, 10 at.% and 30 at.% of erbium were grown by Czochralski method from iridium crucible. In order to obtain a good homogeneity of chemical composition and distribution of erbium, a relatively large rotation rate of the crystals was applied in the growth process, resulting in the convex growth surface. The structural perfection investigated by means of various synchrotron X-ray diffraction methods including monochromatic beam topography, observation of the rocking curves and topographic methods using white synchrotron white beam. The experiments were performed at E2 and F1 experimental stations in HASYLAB.

The most important observed defects were segregation fringes and growth facets. The monochromatic beam topographs confirmed low level of lattice parameter changes connected with the segregation of the erbium and low level of strains in the crystals The segregation fringes were, however, more distinct in crystals with higher erbium concentration. Only in one sample the monochromatic beam topography revealed some “rosettes”, which may be attributed to the dislocation outcrops.

The observed facets formed a characteristic patterns, dependent on the rotation rate of the crystals. The observed facets may be identified as corresponding to {221}, {211} and{301} planes. The first of them are usually forming a core, observed in the most of the crystals, sometimes neighbouring with {211}. The third type of crystals correspond to the planes inclined at 43 and occurs at highest rotation rate. The investigation of the facets was confirmed by the transmission section topographs, which allowed the location growth bands in the intersection of the sample with the synchrotron beam.

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