Molten Alkali Halide Flux Growth of an Extensive Family of Noncentrosymmetric Rare Earth Sulfides: Structure and Magnetic and Optical (SHG) Properties
Twenty new alkali rare earth thiosilicates and thiogermanates with the general formula ALnTS 4 (A = alkali metal, Ln = lanthanide, and T = Si, Ge) were grown as X-ray diffraction-quality single crystals from molten alkali chloride fluxes. These include KNdSiS4, KPrSiS4, RbLnSiS4 (Ln = Ce, Pr, Nd, Gd, Tb, Dy, and Ho), RbLaGeS 4 , CsLnSiS 4 (Ln = La, Pr, and Nd), and CsLnGeS 4 (La, Ce, Pr, Nd, Eu, Gd, and Tb). Herein, we discuss the use of a molten chloride flux growth approach for the preparation of the title compounds and their structure determination via single-crystal X-ray diffraction. In addition, we comment on the magnetic properties of RbNdSiS 4 , CsNdSiS 4 , CsNdGeS 4 , and CsGdGeS 4 , which were found to be paramagnetic for T = 2–300 K and exhibited negative Weiss temperatures with no obvious antiferromagnetic transition down to 2 K. The optical properties of CsLaGeS 4 and CsNdTS 4 (T = Si, Ge) were measured by UV–vis spectroscopy. Second harmonic generation measurements performed on CsLaGeS 4 confirmed the crystallization of the compound in the noncentrosymmetric orthorhombic space group, P2 1 2 1 2 1 ; CsLaGeS 4 was found to be SHG-active with nearly half the intensity of α-SiO 2 upon irradiation with a Nd:YAG 1064 nm laser, and a semiconductor exhibiting a band gap of 3.60 eV based on UV–vis diffuse reflectance measurements.