title: Structure change induced by terminal sulfur in noncentrosymmetric La2Ga2GeS8 and Eu2Ga2GeS7 and nonlinear-optical responses in middle infrared.
abstract: Two new noncentrosymmetric quaternary sulfides, La(2)Ga(2)GeS(8) (1) and Eu(2)Ga(2)GeS(7) (2), have been synthesized by high-temperature solid-state reactions. The structure change on going from 1 to 2 to the known Li(2)Ga(2)GeS(6) (3) nicely shows that the reduced cation charge-compensation requirement causes a decrease in the number of terminal S atoms per formula, which is a key to determining the connectivity of the GaS(4) and GeS(4) building units. Powder sample 2 exhibits a strong second-harmonic-generation (SHG) response of about 1.6 times the benchmark AgGaS(2) at 2.05 μm laser radiation, a non type I phase-matchable behavior, and a comparable transparency region. The SHG intensities of these compounds originate from the electronic transitions from S 3p states to La/Eu/Li-S, Ga-S, and Ge-S antibonding states according to Vienna ab initio simulation package studies.
authors.affiliation: Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People's Republic of China.
authors.forename: Mei-Chun
authors.initials: MC
authors.lastname: Chen
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.forename: Liu-Jiang
authors.initials: LJ
authors.lastname: Zhou
authors.forename: Long-Hua
authors.initials: LH
authors.lastname: Li
authors.forename: Ling
authors.initials: L
authors.lastname: Chen