Enhanced Second-Harmonic-Generation Efficiency and Birefringence in Melillite Oxychalcogenides Sr₂MGe₂OS₆ (M = Mn, Zn, and Cd)

Abstract

Simultaneous regulation and control of non-linear second-harmonic-generation (SHG) coefficients (d eff) and linear birefringence (Δn) of non-centrosymmetric (NCS) crystals is a crucial aspect of improving the non-linear optical (NLO) performance, yet it remains a huge challenge in modern laser techniques and science. Herein, a series of melilite-type oxide-derived NCS oxychalcogenides, Sr2MGe2OS6 (M = Mn, Zn, and Cd), are successfully designed and synthesized through a facile partial isovalent chemical substitution strategy. These isostructural compounds crystallize in the tetragonal NCS space group P4̅21m (no. 113) and feature unique two-dimensional Cairo pentagonal tiling layers composed of heteroligand [GeOS3] and tetrahedral [MS4] asymmetric building units (ABUs). Compared to the parent melilite-type oxides, the derived title compounds not only successfully realize the phase matchability transformation [i.e., from non-phase-matching (NPM) to phase-matching (PM)] but also greatly improve the IR-NLO performance (especially, simultaneously boosting d eff and Δn). Sr2CdGe2OS6 exhibits the best comprehensive performance among oxychalcogenides, including a wide PM cutoff edge (>525 nm), a strong d eff (0.8 × AgGaS2), a giant laser-induced damage threshold (19.2 × AgGaS2), a large band gap (3.62 eV), as well as a broad transmission cutoff region (0.28–12.0 μm). Furthermore, highly distorted [GeOS3] ABU in this melilite-type structure is proved to be the profitable bifunctional NLO-active unit, which can contribute to the search and design of novel IR-NLO crystals with a large Δn and a strong d eff based on the experimental results and theoretical calculations. This work demonstrates the first examples of PM melilite-type oxychalcogenides and offers new perspectives on the phase matchability transformation through the partial isovalent chemical substitution approach, which will play a constructive role in the future design of high-performance IR-NLO heteroanionic materials.

Rational designviadual-site aliovalent substitution leads to an outstanding IR nonlinear optical material with well-balanced comprehensive properties

“…Remarkably, such a transparent range is wider than those of distinguished IR-NLO materials AgGaS 2 (0.48–11.4 μm), 39 ZnGeP 2 (0.74–12 μm), 39 AgGaSe 2 (0.76–17 μm) 39 and other recently reported IR-NLO candidates. 40–45…”

Phase matching achieved by isomorphous substitution in IR nonlinear optical material Ba2SnSSi2O7with an undiscovered [SnO4S] functional motif

“…2a), which is the third example that breaks through the ''4.0 eV wall'' in NCS oxychalcogenides. [40][41][42][43][44][45][46] In addition, optical transmittance curves measured using the single-crystal sample (ca. 0.5 Â 0.5 Â 0.1 mm 3 ) without any treatment (Fig.…”

“…Oxychalcogenides, which combine the performance advantages of both chalcogenides (strong d eff ) and oxides (wide E g ), have recently been recognized as promising candidates for IR-NLO applications. [40][41][42][43][44][45][46] Notably, most of them can be obtained by partial chemical substitution of known oxides, which provides a good structural platform to investigate the influence of hetero-ligand functional groups on the structure-activity relationships. With this in mind, the first PM fresnoite-type oxychalcogenide Ba 2 SnSSi 2 O 7 has been successfully designed and synthesized via isomorphous substitution of the NPM parent Ba 2 TiOSi 2 O 7 .…”

Ba6In2Ge2Te15: a THz birefringent material with an intriguing quasi-[Te5]4− chain possessing large optical anisotropy and an ultrawide transmission range

“…To date, metal chalcogenides have emerged as one of the promising candidates for the design of new IR-THz materials due to their excellent performances and rich structural diversity. [10][11][12][13][14][15][16][17] With the unremitting efforts of materials scientists, many kinds of crystals with favorable birefringence properties have been reported, encompassing Na 7 M II Sb 5 S 12 (M II = Zn, Cd, Hg) (Δn = 0.30-0.37@1064 nm), 18 β-CsBa 2 SnS 4 Cl (Δn = 0.095@1064 nm), 19 Na 2 M II M IV 2 Se 6 (M II = Zn, Hg; M IV = Ge, Sn) (Δn = 0.3249-0.3107@1064 nm), 20 NaBaSbS 3 (Δn = 0.22@1064 nm), 21 Rb 3 NaSn 3 Se 8 (Δn = 0.196@1064 nm), 22 Mg 2 GeSe 4 (Δn = 0.158@1064 nm), 23 Cs 2 ZnSn 3 S 8 (Δn = 0.12@546 nm), 24 CsCu 3 SbS 4 (Δn = 0.232@546 nm), 25 Sr 2 MGe 2 OS 6 (M = Mn, Zn, and Cd) (Δn = 0.064-0.193@2050 nm), 26 etc. However, most of the reported IR birefringent materials are sulfides and selenides, and the research studies on tellurides are very rare.…”