Search

Single crystals of neodymium-doped lanthanum magnesium hexaluminates up to 50 mm in diameter and 80 mm length have been grown by the Czochralski technique along the optical e axis. These single crystals exhibit a core effect which seems to be correlated with a change in the chemical composition between the core and the matrix of the crystal.

The use of LiNbO3 for acoustical and optical devices necessitates the growth of perfect single crystals. γ-ray diffraction provides a nondestructive tool to check mosaic nature and its evolution along the crystals. The γ-ray diffraction experiments were performed on Czochralski grown crystals using reflection planes parallel and perpendicular to the growth direction. The results of these experiments were correlated with X-ray topographs of the same specimens. This characterization shows that lithium niobate crystals have a subgrain structure and that a large grain dis-orientation of up to 1° can exist perpendicular to the growth direction with the grains being rotated around the growth axis. X-ray topographs show that the grain boundaries are parallel to the growth direction for the Z and Y crystals and oblique in the other cases. The mosaic nature can be related to the internal stress and cracking of the crystals.

Blue single crystals of magnesium aluminium spinel doped with nickel have been pulled from the melt, by the Czochralski technique. The transmission spectrum of doped samples show three broad absorption bands. According to the absorption map and the chemical analysis of these crystals, the effective segregation coefficient of Ni 2+ in MgAl 2 0 4 seems to be roughly 1. At T = 80 K. the expected tuning range of the stimulated emission lies from 1.2 to 1.4 μm.