Noncentrosymmetric chalcogenides BaZnSiSe4 and BaZnGeSe4 featuring one-dimensional structures

- BaZnTtSe4 (Tt = Si, Ge) adopt a new noncentrosymmetric structure type.
- One-dimensional chains are built from alternating ZnSe4 and TtSe4 tetrahedra.
- BaZnGeSe4 exhibits a large band gap, good SHG signals, and type-I phase matching.

The two quaternary tetrel-containing selenides BaZnTtSe4 (Tt = Si, Ge) have been prepared by reactions of BaSe, ZnSe, Tt, and Se at 1023 K. They adopt noncentrosymmetric structures (orthorhombic, space group Ama2, Z = 4; a = 11.3055(8) Å, b = 11.2344(7) Å, c = 6.1994(4) Å for BaZnSiSe4; a = 11.3255(6) Å, b = 11.2527(6) Å, c = 6.2917(3) Å for BaZnGeSe4) that are of a new type consisting of one-dimensional chains of edge-sharing tetrahedra alternately centred by Zn and Tt atoms, with Ba cations separating the chains. The structure type is closely related to Sr2SnSe4 and NaEuAsS4. Large optical band gaps of 2.71(2) eV for BaZnSiSe4 and 2.46(2) eV for BaZnGeSe4, as deduced from UV-vis-NIR diffuse reflectance spectra, are consistent with the yellow or orange colour of the crystals. Nonlinear optical measurements on powder samples revealed that BaZnGeSe4 exhibited good second harmonic generation signals and type-I phase-matching behaviour using 2090 nm as the fundamental laser wavelength.

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