Breaking Through the Trade-Off Between Wide Band Gap and Large SHG Coefficient in Mercury-Based Chalcogenides for IR Nonlinear Optical Application

It is substantially challenging for non-centrosymmetric (NCS) Hg-based chalcogenides for infrared nonlinear optical (IR-NLO) applications to realize wide band gap (Eg > 3.0 eV) and sufficient phase-matching (PM) second-harmonic-generation intensity (deff > 1.0 × benchmark AgGaS2 ) simultaneously due to the inherent incompatibility. To address this issue, this work presents a diagonal synergetic substitution strategy for creating two new NCS quaternary Hg-based chalcogenides, AEHgGeS4 (AE = Sr and Ba), based on the centrosymmetric (CS) AEIn2 S4 . The derived AEHgGeS4 displays excellent NLO properties such as a wide Eg (≈3.04-3.07 eV), large PM deff (≈2.2-3.0 × AgGaS2 ), ultra-high laser-induced damage threshold (≈14.8-15 × AgGaS2 ), and suitable Δn (≈0.19-0.24@2050 nm), making them highly promising candidates for IR-NLO applications. Importantly, such excellent second-order NLO properties are primarily attributed to the synergistic combination of tetrahedral [HgS4 ] and [GeS4 ] functional primitives, as supported by detailed theoretical calculations. This study reports the first two NCS Hg-based materials with well-balanced comprehensive properties (i.e., Eg > 3.0 eV and deff > 1.0 × benchmark AgGaS2 ) and puts forward a new design avenue for the construction of more efficient IR-NLO candidates.

Sb4O5I2: Enhancing Birefringence through Optimization of Sb/I Ratio for Alignment of Stereochemically Active Lone Pairs

Birefringent crystals are the key components of functional optics, contributing significantly to scientific and technological advancements. To enhance birefringence, the presence of stereochemically active lone pairs offers a unique opportunity. In fact, strengthening the stereochemical activity and aligning uniformly lone pairs face tough challenges. Herein, an anisotropic layered crystal, Sb4O5I2, is discovered to exhibit enhanced birefringence. The influence of crystal symmetry on the birefringence of Sb4O5X2 (X = Cl, Br, or I) is found to be minor. Instead, the asymmetric nature of ABUCBs (i.e., cis-X3[SbO3]6- and cis-X3[SbO4]8-) plays a crucial role in enhancing the optical anisotropy. And the orientation of these ABUCBs is equally important. We demonstrate that by adjusting the Sb/I ratio from 5:1 to 2:1, all of the intralayer Sb atoms in Sb5O7I-P63 are forced onto the surface position. This structural adjustment leads to strengthened ionic bonding interactions, enhanced activity of the lone pairs, and uniform alignments of the ABUCBs in Sb4O5I2. Consequently, this results in a 6-fold increase in birefringence.

Syntheses, crystal structure, and photoelectric properties of two Zn-based chalcogenidoantimonates Zn-Sb-Q (Q = S, Se)

Metal chalcogenides are a special class of semiconducting materials characterized by their rich structures and compositions, making them a promising option for a broad range of applications in the field of inorganic chemistry. However, the path forward is not without its challenges, notably in the realms of interface management and enhancing carrier concentration. To address these issues, we solvothermally synthesized two novel chalcogenidoantimonates [Zn(tren)]2Sb2Se5 (1) [tren = tris (2-aminoethyl) amine] and [Zn(tepa)H]2Sb2S6 (2) (tepa = tetraethylenepentamine) utilizing transition metal Zn by band gap optimization strategy in the visible region. Both compounds exhibited distinct zero-dimensional cluster structures, with transition metal complex cations acting as structure-directing agents. A comprehensive analysis of the electronic structure, band gap, and photocurrent response of these crystals was undertaken, revealing significantly enhanced photocatalytic properties compared to preceding studies. This research underscores the potential of antimony chalcogenides in the realm of photoelectric properties and promotes the applications of chalcogenides.

Rational Design of a Rare-Earth Oxychalcogenide Nd3 [Ga3 O3 S3 ][Ge2 O7 ] with Superior Infrared Nonlinear Optical Performance

Inorganic chalcogenides have been studied as the most promising infrared (IR) nonlinear optical (NLO) candidates for the past decades. However, it is proven difficult to discover high-performance materials that combine the often-incompatible properties of large energy gap (E_g ) and strong second harmonic generation (SHG) response (d_eff ), especially for rare-earth chalcogenides. Herein, centrosymmetric Cs₃ [Sb₃ O₆ ][Ge₂ O₇ ] is selected as a maternal structure and a new noncentrosymmetric rare-earth oxychalcogenide, namely, Nd₃ [Ga₃ O₃ S₃ ][Ge₂ O₇ ], is successfully designed and obtained by the module substitution strategy for the first time. Especially, Nd₃ [Ga₃ O₃ S₃ ][Ge₂ O₇ ] is the first case of breaking the trade-off relationship between wide E_g (>3.5 eV) and large d_eff (>0.5 × AgGaS₂ ) in rare-earth chalcogenide system, and thus displays an outstanding IR-NLO comprehensive performance. Detailed structure analyses and theoretical studies reveal that the NLO effect originates mainly from the cooperation of heteroanionic [GaO₂ S₂ ] and [NdO₂ S₆ ] asymmetric building blocks. This work not only presents an excellent rare-earth IR-NLO candidate, but also plays a crucial role in the rational structure design of other NLO materials in which both large E_g and strong d_eff are pursued.

Ba5Ga2SiO4S6: a Phase-Matching Nonlinear Optical Oxychalcogenide Design via Structural Regulation Originated from Heteroanion Introduction

Tailored structural regulation to obtain a new non-centrosymmetric (NCS) compound with excellent optical properties is highly desirable but remains a challenge for nonlinear optical (NLO) material design. In this work, centrosymmetric celsian-type BaGa₂Si₂O₈ was selected as a template structure, and a novel NCS oxychalcogenide, namely, Ba₅Ga₂SiO₄S₆, was successfully designed via the introduction of heteroanions under high-temperature solid-state conditions. Ba₅Ga₂SiO₄S₆ adopts the monoclinic space group of Cc (no. 9) and is formed by charges balancing Ba²⁺ cations and discrete [Ga₂SiO₄S₆] clusters made of corner-sharing [SiO₄] and [GaOS₃] tetrahedra. Notably, Ba₅Ga₂SiO₄S₆ exhibits the critical requirements as a potential UV NLO candidate, including a phase-matching second-harmonic generation intensity (∼1.0 × KDP), a beneficial laser-induced damage threshold (1.2 × KDP), a large birefringence (Δn = 0.10@546 nm), and a short UV absorption cutoff edge (ca. 0.26 μm). Furthermore, the theoretical calculation is implemented to provide a deeper analysis of the structure-activity relationship. The investigated example of structural regulation originated from heteroanion introduction in this study may offer a feasible strategy for high-performance NLO candidate design.

Ba6In2Ge2Te15: A THz Birefringent Material with an Intriguing Quasi-[Te5]4- Chain Possessing Giant Optical Anisotropy and Ultrawide Transmission Range

Exploring mid- and far-infrared (MFIR) and even terahertz (THz) birefringent crystal with a large optical anisotropy remains a great challenge. Herein, a novel THz birefringent material Ba6In2Ge2Te15, which contains the...