Effects of Lamp Filament Alignment, Mirror–Lamp System Position, and Downward Tilt During Growth of Lanthanum- and Cerium-Doped Gadolinium Pyrosilicate Crystal Using Optical Floating Zone Method

Lanthanum (La)- and cerium (Ce)-co-doped gadolinium pyrosilicate (Ga2Si2O7: GPS) crystals were grown using the optical floating zone method under several different conditions. The effects of the filament alignments of the halogen lamps, the positions, and the tilt angle of the mirror–lamp (M–L) systems for infrared convergent heating on the solid–liquid interface shapes and the grown crystals were investigated. The interface shape between a grown crystal and a molten zone was found to be highly concave under the conventional growth condition using halogen lamps as heat sources. The concave melt–crystal interface was systematically changed by the filament alignments of lamps, diameter of the grown crystal, positions, and tilt angle of the M–L system. Although we could not suppress the formation of cracks in a grown crystal and realize a transparent crystal, we succeeded in reducing the crack formation in a grown crystal and enhancing the transparency of a grown crystal by controlling the concave crystal–melt interface.