Growth rate anisotropy and absorption studies on β-BaB_2O_4 single crystals grown by the top-seeded solution growth technique

摘要

Beta barium borate (β-BaB_2O_4; BBO) single crystals have been grown from Na_2O flux by the TSSG technique and the observed growth rate anisotropy is reported. The symmetrical conoscopic interference pattern on the c-cut plate confirmed strain-free and optical homogeneity of the crystals. The observed growth habits of as-grown crystals are explained using crystal growth theories. The relative growth rate along different crystallographic directions of BBO can be described by R_([100]) = R_([010]) > R_([001]). The absorption measurements show a nearly 9 nm shift in fundamental absorption edges in X and Z cut samples. Band gap energies measured were 6.45 and 6.2 eV along the X and Z directions, respectively. The absorption spectra near the fundamental absorption edges (AE) follow Urbach's rule.