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.

Synthesis, Structure and Bonding, Optical Properties of Ba4MTrQ6 (M=Cu, Ag; Tr=Ga, In; Q=S, Se)

“…The compound adopts a new structural type that features 1D [AgInS 6 ] 8À polyanionic chains formed by corner-sharing AgS 4 and InS 4 tetrahedra ( Figure 3). Unlike Ba 4 AgGaS 6 and Ba 4 CuInS 6 discussed above, the coordination geometries for the In and Ag atoms are significantly different in Ba 4 AgInS 6 : the corresponding In À S bonds fall into a narrow range from 2.4597(12) to 2.4657 (11) , and a slightly distorted InS 4 tetrahedron is expected; however, for Ag, a more distorted AgS 4 tetrahedron is involved with a significantly larger Ag À S distance range [2.5487(13)-2.688 (3) ]. Such Ag À S and In À S distances are also in accordance with those of analogues, like Ba 2 AgInS 4 .…”

“…Unexpectedly, Ba 4 AgInS 6 (4) crystallizes in the monoclinic P2 1 /c space group with cell parameters of a = 8.7241(10), b = 8.8799 (11), c = 17.793(2) and b = 104.144(4)8. There are overall four Ba cations, one Ag atom, one In atom, and six S anions in the asymmetric unit.…”

Two new phases in the ternary RE–Ga–S systems with the unique interlinkage of GaS4building units: synthesis, structure, and properties

“…Recently, quaternary chalcogenides that contain a rare-earth metal together with a group 13 main-group metal (e.g., Ga and In) are of great interest due to their fascinating structural chemistry and interesting physical properties including magnetic, photo-response, photoelectric, and nonlinear optical (NLO) properties. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] For example, 1D infinite anionic chains containing the compound Ba 2 REMQ 5 (RE = rare-earth metal; M = Ga, In; Q = S, Se, Te) offer flexibility in band gap engineering by controlling the composition and show weak short-range antiferromagnetic interactions between the adjacent RE 3+ cations. 7,9,10 La 3 CuGaSe 7 contains interesting isolated [CuSe 3 ] 4− pyramids and [GaSe 4 ] 5− tetrahedra and exhibits interesting centrosymmetric photo-response behaviour.…”

“…16 Noncentrosymmetric Sm 4 GaSbS 9 and La 4 InSbS 9 exhibit very strong powder second harmonic generation (SHG) responses in the IR range, indicating that they are promising candidates for laser frequency conversion applications. 5,6 Compared with the extensive research studies on quaternary systems, the studies on ternary rare earth metal/gallium/ sulfur (RE/Ga/S) compounds are relatively scarce. The existing examples are limited to only REGa 2 S 4 (RE = Sm, Eu, Yb), 19 LaGaS 3 , 20 RE 6 Ga 3.33 S 14 (RE = La-Nd, Sm-Tb, Y), 21 and RE 3 GaS 6 (RE = Dy, Ho, Er, Y).…”

Syntheses, crystal structures, and NLO properties of the quaternary sulfides RE3Sb0.33SiS7 (RE=La, Pr)

“…Tetrahedrally coordinated triel or tetrel metal chalcogenides have drawn considerable attentions not only for their diverse structural features but also for their second-order nonlinear optical (NLO) activity, such as: AgGaS 2 (AGS) [1], LiGaQ 2 (Q = S, Se, Te) [2], LiInQ 2 (Q = S, Se) [3], BaGa 4 Q 7 [4], K 2 Hg 3 Ge 2 S 8 [5], Li 2 Ga 2 GeS 6 [6], Li 2 In 2 MQ 6 (M = Si, Ge) [7], BaGa 2 MS 6 (M = Si, Ge) [8], Ba 2 BiInS 5 [9], Ba 2 InYSe 5 [10], Ba 4 CuGa 5 Q 12 (Q = S, Se) [11], Li 2 CdGeS 4 [12], Y 3 Zn 0.5 SiS 7 [13], Eu 2 Ga 2 GeS 7 [14], Pb 4 Ga 4 GeQ 12 (Q = S, Se) [15], Ba 3 AGa 5 Se 10 Cl 2 (A = K, Rb, Cs) [16], and ACd 4 Ga 5 Q 12 (A = K, Rb, Cs; Q = S, Se) [17]. Among them, AgGaS 2 is the well-known middle-infrared (mid-IR) benchmark NLO material exhibiting a high second-harmonic generation (SHG) coefficient and a wide transparent range.…”