Pb4O3I2: A Lead Oxyhalide IR Optical Crystal with an Unprecedented 1∞[O3Pb4] Chain Featuring a Wide Transmittance Range and Large Birefringence

Among the infrared (IR) optical material systems, the heavy-metal oxyhalide system has become an emerging system in recent years. Introducing heavy-metal cations and halogen anions with large atomic numbers is conducive to widening the IR transparency window and improving the birefringence value. Our experiments focus on the PbO-PbI2 system and find a new lead oxyhalide, Pb4O3I2. The structure of Pb4O3I2 is mainly composed of [OPb4] basic structure units, and triple-row [OPb4] units further connect to form unprecedented 1∞[O3Pb4] infinite chains. Pb4O3I2 exhibits a wide IR transmission range from 0.49 to 15.0 μm, and theoretical calculation shows that Pb4O3I2 has a large birefringence of Δn = 0.098 @1064 nm. The results show that Pb4O3I2 is an example of an IR optical material with good optical properties in heavy-metal oxyhalides, which significantly enriches the diversity of oxyhalides.

Pb2(SeO3)(SiF6): the first selenite fluorosilicate with a wide bandgap and large birefringence achieved through perfluorinated group modification

Birefringent crystals serve as the core elements of polarizing optical devices. However, the inherent challenge of balancing bandgap and birefringence poses a significant hurdle in designing crystals with excellent overall performance. In this study, we propose a novel approach, namely modification with perfluorinated groups, to achieve dual enhancement of the bandgap and birefringence of selenite materials. We have successfully synthesized the first selenite fluorosilicate, namely, Pb2(SeO3)(SiF6). This compound exhibits a three-dimensional structure composed of two-dimensional lead selenite layers bridged by SiF6 octahedrons. Notably, by introducing a perfluorinated SiF6 group, the bandgap of the lead selenite compound has been expanded to 4.4 eV. Furthermore, Pb2(SeO3)(SiF6) demonstrates a large birefringence (0.161 @ 546 nm), surpassing most of the selenite compounds with a bandgap larger than 4.2 eV. Theoretical calculations suggest that the large birefringence of Pb2(SeO3)(SiF6) can be attributed to the synergistic effects of SeO3, PbO4 and PbO3F4 polyhedrons. Our research not only pioneers a new system for selenite materials, enriching the diversity of selenite structures, but also provides a design methodology for obtaining wide bandgap birefringent selenite.

Cadmium Hydroxyl Chloride with Balanced Band Gap and Second-Harmonic-Generation Response

Ultraviolet (UV) nonlinear-optical (NLO) materials are crucial in laser technology due to their ability to modulate light frequency. In this work, when d10 cations, hydroxyl groups, and Cl atoms were combined, a cadmium double salt, Cd(OH)Cl, was synthesized by a simple hydrothermal method. It has a large phase-matched second-harmonic-generation (SHG) response at 1064 nm (2.5 × KDP) with a short UV-cutoff edge (260 nm), which can be applied in a solar-blind UV band. Theoretical calculations suggest that [Cd(OH)3Cl3] groups lead to a large SHG response. Our work may shed light on the exploration of new NLO materials in metal hydroxyl chlorides.

Synthesis, structure and characterization of Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers

A new mixed anionic compound Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers has been synthesized, and millimeter-scale single crystals of Cd2TeO3Cl2 have been grown by the vertical Bridgman method with CdCl2 as the flux. Cd2TeO3Cl2 crystallizes in the centrosymmetric P1̄ (no. 2) space group, and shows a mixed cationic layer structure constituted by distorted [TeO3] motifs, mixed anionic [Cd2O6Cl4] chains, and [Cd2O6Cl4] octahedral dimers. Experimental and theoretical results show that Cd2TeO3Cl2 is a direct band gap compound with an experimental band gap of ∼4.25 eV. Meanwhile, the compound has good optical transmittance in the 3-5 μm atmospheric window. The results indicate that Cd2TeO3Cl2 could be used as a promising mid-IR window material, and could enrich the chemical and structural diversity of oxides.

Sb5O7I: Exploration of Ternary Antimony-Based Oxyhalide as a Nonlinear-Optical Material

Metal oxyhalides are attracting extensive interest for their enchanting structures and diverse properties. Herein, a ternary antimony oxyiodide, Sb₅O₇I with the new hexagonal noncentrosymmetric P6₃ structure is systematically surveyed by focusing on its nonlinear-optical (NLO) behavior. Its two-dimensional structure is constructed by {Sb₂[Sb₃O₇]}_∞⁺ layers separated by charge-balanced I^- anions. The second-harmonic-generation measurement result suggests that Sb₅O₇I is NLO-active, and the effect is assigned to the [SbO₃]^3- triangular pyramids' contribution. Sb₅O₇I shows a direct optical energy gap of 3.22 eV, which is the largest among all reported ternary oxyiodides. This work is the first investigation of ternary NLO Sb-based oxyhalides and enriches the study of metal oxyhalides as promising NLO materials.

Second-Harmonic Generation-Positive Na2Ga2SiS6 with a Broad Band Gap and a High Laser Damage Threshold

The development of high-power solid-state lasers is in urgent need of new infrared nonlinear optical (IR NLO) materials with a wide band gap and a high laser-induced damage threshold. A new infrared nonlinear optical material Na₂Ga₂SiS₆ has been synthesized for the first time, crystallizing in the Fdd2 (no. 43) noncentrosymmetric space group. Its three-dimensional tunnel framework consists of two typical NLO active motifs [GaS₄] and [SiS₄], with Na⁺ cations located inside the tunnels. Na₂Ga₂SiS₆ exhibits comprehensive optical properties, namely, a wide transmission range, a high laser-induced damage threshold (10 × AgGaS₂), a type-I phase-matching second-harmonic generation response (0.2 × AgGaS₂), and especially a wide band gap (3.93 eV), which is the largest in the A₂M^III₂M^IVQ₆ (A = alkali metals; M^III = IIIA elements; M^IV = IVA elements; Q = S and Se) family. Therefore, Na₂Ga₂SiS₆ does not produce two-photon absorption under a 1064 nm laser pump and could be used in high-energy laser systems, which makes Na₂Ga₂SiS₆ a promising candidate for high-energy IR NLO applications.

Na4Ga8S14: A Ga-riched wide band gap ternary alkali-metal sulfide with unique [Ga12S42] 12-menbered rings

A Ga-riched ternary alkali-metal sulfide Na4Ga8S14 has been synthesized by high temperature solid-state reaction. It crystallizes in the centrosymmetric Pbca (no. 61) space group with cell parameters a = 13.5260(4)...