Cs₄Zn₅P₆S₁₈I₂: the Largest Birefringence in Chalcohalide Achieved by Highly Polarizable Nonlinear Optical Functional Motifs

Abstract

Chalcohalides not only keep the balance between the nonlinear optical (NLO) coefficient and wide band gap, but also provide a promising solution to achieve sufficient birefringence for phase‐matching ability in NLO crystals. In this study, a novel chalcohalide, Cs4Zn5P6S18I2 (1) is successfully synthesized, by incorporating the highly electropositive Cs and the large electronegative I element into the zinc thiophosphate. Its 3D open framework features an edge‐shared by distorted [ZnS4], ethanol‐like [P2S6], and unusual [ZnS2I2] polyhedrons, which is inconsistent with the soft‐hard‐acids‐bases theory. Remarkably, compound 1 simultaneously exhibits the large second‐harmonic generation (SHG, 1.1×AgGaS2, @1.3 µm) and a wide band gap (3.75 eV) toward a high laser‐induced damage threshold (16.7×AgGaS2, @1.06 µm), satisfying the rigorous requirements for a prominent infrared NLO material with concurrent SHG intensity (≥0.5×AGS) and band gap (≥3.5 eV). Moreover, to the best of the knowledge, the experimental result shows that phase 1 has the largest birefringence (0.108, @546 nm) in chalcohalide and meets phase‐matching behavior demand originating from the polarizable anisotropy of NLO‐functional motifs. This finding may provide great opportunities for designing birefringent chalcohalides.

β-CsHg2I5, a compound with rare [Hg2I5] dimers and large optical anisotropy

“…The diffuse reflectance spectrum of pure phase β-CsHg 2 I 5 was recorded using a Shimadzu SolidSpec-3700DUV spectrophotometer at room temperature, and the reflectance spectral data were converted to absorption spectral data using the Kubelka–Munk formula: α / S = (1 − R )2/(2 R ), ( R = reflectance; α = absorption; and S = scattering). 47–50…”

Mixed Anionic M(S/X)6 Polyhedra as Symmetry-Breaking Motifs to Enhance the Infrared Nonlinear Optical Response in Y–M–S–X (M = Ga, Ge; X = Cl, Br)

“…Introducing highly electronegative halide atoms into sulfide compounds to construct mixed anionic units has the potential to induce a blue shift in the absorption cutoff edge. This effect widens the E g , thereby improving the material’s resistance to laser damage and enhancing its stability and reliability in optical devices and laser systems. − Furthermore, the use of halogen atoms with varying sizes and electronegativities (such as Cl and Br) can induce distortions of NLO motifs, amplifying the material’s polarity and NLO effect.…”