Edge-defined film-fed (EFG) growth of rare-earth orthovanadates REVO_4 (RE = Y, Gd): Approaches to attain high-quality shaped growth

摘要

In spite of their superior laser and polarizer properties rare-earth orthovanadates (REVO_4) single crystals have not been adopted yet into extensive industrial applications because of crystal growth difficulties. The main problems of CZ technique are compositional change and diameter instability. This work presents the first attempt to apply the edge-defined film-fed growth (EFG) technique by which well-shaped REVO_4 crystals have been grown directly. The capillary properties of YVO_4 and GdVO_4 melt have been measured. The applicability of shaped growth for rare-earth orthovanadate family was approved by successful EFG growth of transparent rod-like macro-defect-free single crystals of YVO_4 and GdVO_4. We address two main approaches to enhance the quality of EFG crystals: (i) meniscus and crystal shape stability dependence on die top shape and (ii) the strategy of effective operating control. Concave die top was found to be the best choice for high-quality EFG growth of REVO_4 along [001] direction. The spectral analysis of weight signal from growing crystal was shown to be a useful feedforward clue to prevent crystallinity degradation at a very early stage. A reasonable stability of the EFG process was achieved using [211], [101], [001] and [100] pulling directions.