Ba₆Zn₇Ga₂S₁₆: A Wide Band Gap Sulfide with Phase-Matchable Infrared NLO Properties

Abstract

High-performance infrared (IR) nonlinear optical (NLO) materials with large laser damage thresholds (LDTs) are urgently needed because the current commercially available AgGaS2, AgGaSe2, and ZnGeP2 suffer their very low LDTs which shorten significantly their service lifetimes. Here, a novel sulfide, Ba6Zn7Ga2S16 with a very wide band gap of 3.5 eV, has been discovered. This compound crystallizes in the chiral trigonal R3 space group with a novel 3D framework that is constructed by ZnS4 tetrahedra, Zn3GaS10 supertetrahedra (a T2-type), and Zn3GaS10 quadri-tetrahedral clusters via vertex-sharing. Such a novel structure exhibits desirable features which suggest a promising NLO material: phase-matchability (PM), good NLO efficiency (about half that of benchmark AgGaS2), and the highest LDT among PM chalcogenides (28 times that of benchmark AgGaS2). In addition, the density functional theory (DFT) calculations confirm its PM behavior and reveal that the second harmonic generation (SHG) origin is mainly ascribed to the transition process from S-3p to Ga-4p, Zn-3p, Zn-3d, and Ba-5d states; the calculated d 11 coefficient of 6.1 pm/V agrees well with experimental values.

A2SnS5: A Structural Incommensurate Modulation Exhibiting Strong Second‐Harmonic Generation and a High Laser‐Induced Damage Threshold (A=Ba, Sr)

“…The optical band gaps of Ba 2 SnS 5 and Sr 2 SnS 5 were determined by UV/Vis/NIR diffuse‐reflectance spectroscopy to be 2.38 eV (Figure b), and are thus close to those of Ba 2 HgS 5 (2.4 eV) and AgGaS 2 (2.56 eV) . The Raman spectra in Figure d show that the characteristic peaks between 400–500 cm −1 are related to the S−S bond stretching vibrations of the S 3 2− groups, which are consistent with those reported in Sr 6 Sb 6 S 17 .…”

“…The LIDTs of the polycrystal samples were assessed with a 1064 nm pulse laser (pulse width: 10 ns) to be Ba 2 SnS 5 (18.2 MW cm −2 ) and Sr 2 SnS 5 (16.4 MW cm −2 ), which are about 8 and 7 times larger than that of AgGaS 2 (2.3 MW cm −2 ), respectively (Table ). Considering that the E g values of 2.38 eV for Ba 2 SnS 5 and Sr 2 SnS 5 are smaller than that of AgGaS 2 ( E g =2.56 eV), their higher LIDTs seem to be contrary to the general observation that the E g and LIDT are somewhat positively correlated. The thermal expansion anisotropy (TEA) is a key factor determining the thermal damage level caused by the incident laser as a material with a smaller TEA is less likely to be damaged by the temperature increase upon laser irradiation, leading to a higher LIDT .…”

“…Usually, in a structure, a distorted M/Q polyhedron (M=Group 14–16 metal; Q=S, Se) is introduced as the primary anionic structure building unit to give rise to a good SHG coefficient, and simultaneously, an electropositive alkali/alkaline‐earth metal cation is involved to increase the E g . To date, many chalcogenides have been thus obtained, and some of them exhibit excellent IR‐NLO properties, such as Ba 23 Ga 8 Sb 2 S 38 , Ba 6 Zn 7 Ga 2 S 16 , A 2 BaSnS 4 (A=Li, Na), Li[LiCs 2 Cl][Ga 3 S 6 ], and Na 2 ZnGe 2 S 6 , and all of them exhibit classical periodic structures.…”

Li[LiCs2Cl][Ga3S6]: A Nanoporous Framework of GaS4 Tetrahedra with Excellent Nonlinear Optical Performance

“…The SHG intensities increase with the particle size and reach a plateau at large particle size, indicating a phase‐matching behavior. The relative SHG intensities of 1 and AGS are nearly independent of particle size, and the SHG intensity of 1 in the particle size range of 150–200 μm is approximately 0.7 times that of AGS (Figure b), which is comparable with those of wide band gap IR NLO crystals, such as BaB 2 S 4 (0.7 AGS), Li 2 ZnSiS 4 (1.1 AGS), and Na 2 ZnGeS 6 (0.9 AGS), and larger than Ba 6 Zn 7 Ga 2 S 16 (0.5 AGS) . The dipole moment calculation demonstrates that the highly orientated GaS 4 tetrahedra in the [Ga 3 S 6 ] 3− host are responsible for the good SHG efficiency (Supporting Information).…”

Strong SHG Response via High Orientation of Tetrahedral Functional Motifs in Polyselenide A2Ge4Se10 (A = Rb, Cs)

“…; Q = S, Se) . The flexible assembly of these units produces some IR‐NLO materials, such as 3‐D BaGa 4 S 7 , BaGa 4 Se 7 , Li 2 Ga 2 GeS 6 , A 2 Hg 3 M 2 S 8 (A = K, Rb; M = Ge, Sn), Ba 4 CuGa 5 Q 12 (Q = S, Se), Ba 2 Ga 8 MS 16 (M = Si, Ge), and Ba 6 Zn 7 Ga 2 S 16 , 2‐D Na 2 Ge 2 Se 5 , and [A 3 X][Ga 3 PS 8 ] (A = K, Rb; X = Cl, Br), 1‐D A 4 Ge 4 Se 12 (A = Rb, Cs), APSe 6 (A = K, Rb), and BaHg 2 Se 3 , and molecular ones, A 4 GeP 4 Se 12 (A = K, Rb, Cs), Cs 5 P 5 Se 12 , and Ba 23 Ga 8 Sb 2 S 38 . These discoveries highlight the guiding role of NLO functional motifs in the development of new IR‐NLO materials.…”