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Two quaternary sulfides RE 3 Sb 0.33 SiS 7 ( RE =La, Pr) have been prepared from stoichiometric mixtures of elements at 1223 K in an evacuated silica tube. They are the first examples of chalcogenides in the quaternary RE /Si/Sb/ Q (RE=rare earth metal; Q =S, Se, Te) system. These two isostructural materials crystallize in the Ce 3 Al 1.67 S 7 structure type in the hexagonal space group P 6 3 . Their structure features one-dimensional chains of face-sharing SbS 6 octahedra running parallel to the c direction surrounded by the discrete SiS 4 tetrahedra and RE cations. The La 3 Sb 0.33 SiS 7 exhibits a SHG signal about 0.5 times that of the commercially used IR NLO material AgGaS 2 at 2.05 μm laser. The optical gap of 1.92 eV for La 3 Sb 0.33 SiS 7 was deduced from UV/Vis reflectance spectroscopy. [ABSTRACT FROM AUTHOR]

Non-centrosymmetric structure is the most important prerequisite for a nonlinear-optical (NLO) material. Herein, a non-centrosymmetric phosphate LiRb 2 Y 2 (PO 4) 3 (1), which is transparent down to ultraviolet region, was synthesized by the high-temperature solid-state reactions and solution method. Its crystal structure features a three-dimensional framework composed of corner-sharing YO 6 octahedra and PO 4 tetrahedra. Although it is isostructural to the known langbeinite-type sulfate K 2 Zn 2 (SO 4) 3 , 1 exhibits a sharply enhanced NLO effect (about 3 times that of K 2 Zn 2 (SO 4) 3). On the basis of structural analysis and theory calculations, the improved performance of compound 1 is mainly ascribed to the aliovalent replacement of ZnO 6 by YO 6 octahedra. Our studies indicated that it may be an effective method to develop non-centrosymmetric compounds by aliovalent substitution. By aliovalent-substituted synthesis method based on K 2 Zn 2 (SO 4) 3 , a new phosphate LiRb 2 Y 2 (PO 4) 3 was synthesized and exhibits a sharply enhanced second-harmonic generation (SHG) effect. Image 1 [ABSTRACT FROM AUTHOR]