Defect Structure Formed at Different Stages οf Growth Process in Erbium, Calcium and Holmium Doped $YVO_{4}$ Crystals

The defect structure of $YVO_{4}$ single crystals doped with $Er^{3+},$ $Ho^{3+}$ and $Ca^{2+}$ were studied by X-ray diffraction topographic methods, using laboratory and synchrotron radiation sources. Variously developed block structure was the dominating imperfection of the investigated crystals observed both in conventional Lang and synchrotron topographs. The evaluation of block misorientation was realised by means of superimposed projection and section white beam synchrotron radiation topographs. More possibilities of following the mutual rotation of blocks were provided by means of white beam synchrotron radiation WBSR projection topographs exposed through the fine mesh.