Polysulfide Anions [S_x]²⁻ (x = 2, 3, 4, 5): Promising Functional Building Units for Infrared Nonlinear Optical Materials

Abstract

Infrared nonlinear optical (IR NLO) materials play significant roles in laser technology. The novel functional building units (FBUs) are of great importance in constructing NLO materials with strong second harmonic generation (SHG). Herein, polysulfide anion [Sx]2− (x = 2, 3, 4, 5) units are investigated on NLO‐related properties and structure‐performance relationships. Theoretical calculations uncover that the [Sx]2− (x = 2, 3, 4, 5) units are potential IR NLO FBUs with large polarizability anisotropy (δ), hyperpolarizability (β) and wide HOMO–LUMO gap. Fourteen crystals including [Sx]2− (x = 2, 3, 4, 5) units are calculated and analyzed. The results show that these units can result in a wide IR transmittance range, significant SHG effects, wide band gap Eg (Na2S4: Eg = 3.09 eV), and large birefringence Δn [BaS3 (P21212): Δn = 0.70]. More importantly, it is highlighted that the crystal materials including with [Sx]2− (x = 2, 3, 4, 5) groups are good candidates for the exploration of the outstanding IR NLO materials.

Homoatomic Polychalcogenide Nonlinear Optical Anionic Groups with Ultra-Large Optical Anisotropy

“… a Experimental and calculated values for the benchmark materials AgGaS 2 , AgGaSe 2 , and ZnGeP 2 are also listed for comparison. The term “refs” is used to indicate the literature provenance of the structures. b Superscript indicates that the structures are designed in this study. c Calculated results can also refer to refs , . …”

“…As an important branch of chalcogenides, HAPCs have been extensively studied in terms of their chemical and material properties. However, their NLO performance and related NLO “structure–property correlations” have not been fully exploited, although several related studies on polysulfides have emerged in our research process very recently. , In order to comprehensively evaluate the practical mid-IR NLO properties, including optical band gaps, NLO effects, birefringence, IR transparency, elastic properties, and thermal conductivities, here, we have selected totally 55 “simple” but typical HAPCs from the crystal database or by design, i.e., the binary alkali metal HAPCs A 2 Q n ( n = 2, 3, 4, 5; A = Na, K, Rb, Cs; Q = S, Se, Te) and their ternary analogues, to systematically investigate the evolution of NLO and birefringent properties, with typical polyanionic structures based on the state-of-the-art first-principles approach. By mining the intrinsic NLO mechanism, we identify the HAPC anionic groups as novel mid-IR NLO motifs, providing unique NLO or birefringent performance for the design of advanced optoelectronic materials.…”

Theoretical insight on structure, electronic, and optical properties of two d 0–d 10 electron transition-metal oxyhalides SHG materials

“…The SHG responses of the oxyhalides are further discussed. The length-gauge formalism [66,67] was adopted to calculate the static second-order optical susceptibility χ (2) (d ikj = χ (2) ikj /2). It has been proven to be successful in predicting the optical coefficients for semiconductors and insulators [47,68].…”

“…It has been proven to be successful in predicting the optical coefficients for semiconductors and insulators [47,68]. The imaginary part of χ (2) at a zero-frequency limit could be expressed [63,69] as the following formulas ( 4) and ( 5), (…”

“…Nonlinear optical (NLO) materials have triggered enormous interest, especially using the second harmonic generation (SHG) response to achieve cascaded laser frequency conversion for tunable wavelength laser output [1]. It has a wide range of applications in advanced optical technology of civilian and military equipment such as optical communications and medical surgery [2][3][4]. Hence, persistent endeavors have been initiated in the pursuit of high-performance NLO materials.…”