Cadmium-rare earth oxyborates Cd4ReO(BO3)3 (Re=Y, Gd, Lu): congruently melting compounds with large SHG responses

A new series of cadmium-rare earth (Re) oxyborates Cd4ReO(BO3)(3) (Re = Y, Gd, Lu) have been synthesized through high-temperature solid-state reactions in platinum crucibles. In their crystal structures, ReO6 (Re = Y, Gd, Lu) and CdOn (n = 6, 8) are distorted polyhedra interconnected via shared edges and corners in a 3D framework with tunnels along the c-axis, where all B atoms are located. BO3 planar triangles lie approximately parallel to the (001) plane. The combination of triangular BO3 groups with pi-conjugated systems and the d(10) Cd2+ cation with polar displacement produces large SHG responses. Second harmonic generation ( SHG) measurements indicate that Cd4YO(BO3)(3), Cd4GdO(BO3)(3), and Cd4LuO(BO3)(3) feature large SHG responses that are approximately 5.2, 5.0, and 5.3 x KH2PO4 (KDP), respectively. They are all phase matchable nonlinear optical materials that have wide transparent regions ranging from UV to near IR. These title compounds melt congruently, suggesting that the Cd4ReO(BO3)(3) (Re = Y, Gd, Lu) complexes are very promising NLO materials. Their electronic structures and optical properties were analyzed by using the Vienna ab initio theoretical method.