Second-Harmonic-Generation-Active Oxyhalides: CuSb 2 O 3 X (X = Cl, Br).

Metal oxyhalides have attracted broad interest recently because of their diverse structures and versatile properties. Here, two oxyhalides, CuSb 2 O 3 Cl ( 1 ) and CuSb 2 O 3 Br ( 2 ), were studied by focusing on their nonlinear-optical properties. They are crystallized in the noncentrosymmetric monoclinic Cc structure, and the layered structures could be derived from a 1:1 combination of CuX- (X = Cl, Br) and Sb 2 O 3 -type slabs. Their energy gaps were determined to be 2.76 and 2.64 eV. The second-harmonic-generation (SHG) test suggests that they are nonlinear-optical-active, and the effects are ascribed to the contribution of CuX 3 O units. Meanwhile, the SbO 3 units' arrangement has a small contribution to the SHG effects. This work is the pioneer SHG investigation of the M I -M III -O-X (M I = Cu, Ag; M III = trivalent As, Sb, Bi; X = halogen) family.