Noncentrosymmetric Ba6In2Q10 (Q = S, Se): Structural Chemistry and Nonlinear-Optical Activity.

The indispensable condition for laser frequency-doubling crystal materials is that they crystallize in the noncentrosymmetric (NCS) structures. Here, ternary NCS Ba6In2S10 (1) and Ba6In2Se10 (2) (P63) were synthesized via conventional solid-state reactions. Their zero-dimensional structures feature isolated InQ4 tetrahedra and Q22- (Q = S, Se) dimers that are separated by Ba2+ counter cations. The structural relevance and differences with the centrosymmetric Ba12In4S19 and Ba12In4Se20 are analyzed in detail. Both 1 and 2 show obvious laser frequency-doubling activity, and their optical band gaps are 3.72 and 1.78 eV, respectively. This work provides a new type of IR nonlinear-optical materials.