La 3 Ga 3 Ge 2 S 3 O 10 : An Ultraviolet Nonlinear Optical Oxysulfide Designed by Anion‐Directed Band Gap Engineering

Oxychalcogenides: A Promising Class of Materials for Nonlinear Optical Crystals with Mixed-Anion Groups

Infrared nonlinear optical (IR NLO) materials are of great significance in the development of IR laser technology. But rationally designing high-performance IR NLO materials remains a huge challenge due to the conflict between the necessary properties required for NLO materials. Notably, oxychalcogenides with mixed-anion groups have drawn extensive interest as a family of important IR NLO candidates because they integrate the property advantages of oxides and chalcogenides by chemical substitution engineering. In this review, we provide a survey of reported oxychalcogenides and aim to present the development of NLO oxychalcogenides from the perspective of rational design of their structural chemistry. Furthermore, we focus on the relationships between partial substitution and structural symmetry as well as optical properties. These provide some helpful guidance for the further exploration and design of novel oxychalcogenide materials with excellent NLO performance in the future.

A High-Performance Nonlinear Optical Crystal with a Building Block Containing Expanded π-Delocalization

Common nonlinear optical (NLO) crystals consist of traditional functional building blocks with inherent optical limitation. Herein, inspired by traditional (B₃ O₆ )^3- inorganic building block, we theoretically identified a new type of organic functional building blocks and then successfully synthesized the first cyamelurate NLO crystal, Ba(H₂ C₆ N₇ O₃ )₂  ⋅ 8 H₂ O. To our surprise, the constituent (H₂ C₆ N₇ O₃ )^- building block is not in structurally optimal arrangement, but Ba(H₂ C₆ N₇ O₃ )₂  ⋅ 8 H₂ O exhibits excellent optical properties including wide band gap of 4.10 eV, very large birefringence of 0.24@550 nm, and exceptionally strong second-harmonic generation (SHG) response of about 12×KH₂ PO₄ . Both the SHG response and birefringence are much larger than those of commercial NLO crystal β-BaB₂ O₄ with optimally aligned (B₃ O₆ )^3- building block. Theoretical calculations suggest that the expanded π-conjugation delocalization within (H₂ C₆ N₇ O₃ )^- vs (B₃ O₆ )^3- should be responsible to the enhanced performance. This work implies that there is still much room to develop new NLO crystals with excellent functional building blocks that may be longly neglected.

Sr3 [SnOSe3 ][CO3 ]: A Heteroanionic Nonlinear Optical Material Containing Planar π-conjugated [CO3 ] and Heteroleptic [SnOSe3 ] Anionic Groups

Inorganic heteroanionic materials are attracting increasing attention for exploring new nonlinear optical (NLO) materials because they could better satisfy the necessary but conflicting properties of NLO crystals, e.g. large SHG response and wide band-gap. Up to now, the reports on heteroanionic NLO materials have mainly focused on ultraviolet or visible oxide-based fluoroborates, fluorophosphates, borate-phosphates and borate-iodates. However, chalcogenides containing different kinds of anionic groups have barely been reported. Herein, we have synthesized the first oxychalcogenide-carbonate, Sr₃ [SnOSe₃ ][CO₃ ] that contains two different kinds of anionic groups, [SnOSe₃ ] and [CO₃ ]. It crystallizes in a noncentrosymmetric space group and exhibits fascinating NLO properties, including a large SHG response (≈1×AGS), sufficient birefringence (0.12 @1064 nm), wide band-gap (3.46 eV) and high laser damage threshold (240 MW cm^-2 ). These make Sr₃ [SnOSe₃ ][CO₃ ] a promising NLO crystal.

Na4B8O9F10: A Deep-Ultraviolet Transparent Nonlinear Optical Fluorooxoborate with Unexpected Short Phase-Matching Wavelength Induced by Optimized Chromatic Dispersion

Exploring significant ultraviolet/deep-ultraviolet nonlinear optical (NLO) materials is hindered by rigorous and contradictory requirements, especially, possessing a moderate optical birefringence to meet phase-matching (PM). Except for suitable birefringence, small chromatic dispersion is also crucial to blue-shift the PM wavelength. Here, the introduction of fluorinated tetrahedral boron-centred chromophore strategy was proposed to optimize the chromatic dispersion. Herein, [BF4]- unit with large HOMO-LUMO band gap was introduced to Na-B-O-F system and Na4B8O9F10 was designed and synthesized successfully for the first time. Na4B8O9F10 with optimized chromatic dispersion can achieve a short second harmonic generation PM wavelength of 240 nm with a relatively small birefringence (cal. 0.036@1064 nm). Notably, Na4B8O9F10 is the first acentric crystal with [BF4]- unit among reported metal-fluorooxoborate system, involving isolated [BF4]- and novel [B7O10F6]5- fundamental building blocks.