Li 3 B 8 O 13 X (X = Cl and Br): Two New Noncentrosymmetric Crystals with Large Birefringence Induced by BO 3 Units.

Enthusiasm for the exploration of nonlinear alkali metal borates remains high. Focusing on the Li-B-O-X (X = Cl and Br) system, two examples of noncentrosymmetric borates, Li 3 B 8 O 13 Cl and Li 3 B 8 O 13 Br, were obtained using a high-temperature solution method under vacuum conditions. Structurally, the Li 3 B 8 O 13 X crystals exhibit two independent alternately arranged three-dimensional B-O network structures formed by the basic building block unit B 8 O 16 . The performance measurements demonstrate their short ultraviolet cutoff edges. The theoretical calculation indicates that the BO 3 units dominate the contribution to their large optical anisotropy with the birefringence, 0.094 and 0.088@1064 nm for Li 3 B 8 O 13 Cl and Li 3 B 8 O 13 Br, respectively.