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Exploring new material systems is a highly significant task in the field of inorganic chemistry. A new mixed-valent selenium compound, Hg 3 Se(SeO 3 )(SO 4 ), was successfully synthesized through in situ reactions. This compound exhibits a novel three-dimensional structure composed of Hg 3 Se(SO 4 ) layers bridged by SeO 3 trigonal pyramids. It is the first structure containing (SeO 3 ) 2- , (SO 4 ) 2- , and Se 2- simultaneously. In addition, Hg 3 Se(SeO 3 )(SO 4 ) possesses a wide bandgap (3.5 eV), moderate birefringence (Cal:0.064@546 nm, Exp:0.069@546 nm), a high laser-induced damage threshold (23.35 MW cm -2 ), and a wide transmittance window (0.28-6.6 μm). Our work demonstrates that mixed-valent (+4, -2) selenite selenide can be potential optical materials for the mid-infrared region.

Two new mixed-anion cerium iodates, namely, Ce(IO 3 ) 3 F and Ce(IO 3 ) 2 (NO 3 ), have been rationally designed through the integration of hybrid anionic functional building blocks (FBBs). The structure of Ce(IO 3 ) 3 F features a novel [Ce(IO 3 ) 3 F] bilayer, and the material exhibits large birefringence (0.225 @546 nm). The structure of Ce(IO 3 ) 2 (NO 3 ) features [Ce 3 (IO 3 ) 6 ] 3+ triple layers that are further linked by planar NO 3 - units. Ce(IO 3 ) 2 (NO 3 ) shows a moderate SHG response (1 × KDP) and a high laser-induced damage threshold value (22 × AgGaS 2 ). This work demonstrates that the rich coordination geometries of cerium cations facilitate tuning of the structures of related compounds through modulating anionic FBBs.

Organic-inorganic hybrid nonlinear optical (NLO) materials are highly anticipated because of the integration of both merits of the organic and inorganic moieties. Herein, the 2-pyrimidinone cation (C 4 H 5 N 2 O) + has been incorporated into the iodate system to form two polymorphic organic-inorganic hybrid iodates, namely, α- and β-(C 4 H 5 N 2 O)(IO 3 )·HIO 3 . They crystallize in different polar space groups ( Ia and Pca 2 1 ), and their structures feature one-dimensional (1D) chain structures composed of (C 4 H 5 N 2 O) + cations, IO 3 - anions, and HIO 3 molecules interconnected via hydrogen bonds. α- and β-(C 4 H 5 N 2 O) (IO 3 )·HIO 3 exhibit strong and moderate second-harmonic-generation (SHG) responses of 6.4 and 0.9 × KH 2 PO 4 (KDP), respectively, the same band gaps of 3.65 eV, and high powder laser-induced damage threshold (LIDT) values [51 and 57 × AgGaS 2 (AGS)]. The results of theoretical calculations revealed that the large SHG effect of α-(C 4 H 5 N 2 O)(IO 3 )·HIO 3 originated from the IO 3 and HIO 3 groups. This work indicates that (C 4 H 5 N 2 O) + is a potential group for designing new NLO materials with brilliant optical performances.

A new polar hafnium iodate, CsHfF 4 (IO 3 ), was successfully designed and synthesized by integrating fluorinated hafnium-oxygen polyhedra (HfF 6 O 2 ) and IO 3 - anionic functional groups. Owing to the weak electronic effect of Hf 4+ and the bond-network-induced out-of-center distortion of the HfF 6 O 2 dodecahedra, CsHfF 4 (IO 3 ) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KH 2 PO 4 ) and a rather large band gap (4.47 eV), which is the largest among the d 0 transition-metal iodates. In addition, CsHfF 4 (IO 3 ) possesses a wide transparent region (0.27-9.9 μm), a large birefringence for phase-matching (0.161), and a high laser-induced damage threshold (55.41 MW cm -2 , 26 × AgGaS 2 ) and is nonhygroscopic. This work indicates that the integration of mixed-ligand acentric coordination polyhedra and functional groups containing lone electron pairs is an effective strategy for developing novel inorganic nonlinear-optical materials with balanced overall properties.

Large-sized crystals of the quaternary iodate NaVO 2 (IO 3 ) 2 (H 2 O) (NVIO) with centimeter-scale dimensions (23 mm × 18 mm × 6 mm as a representative) have been successfully grown by the top-seeded hydrothermal method. Linear optical properties have been measured, including the optical transmission spectrum and refractive index. The NVIO crystal possesses an optical window with high transmittance (above 80%) over the range of 500-1410 nm and exhibits strong optical anisotropy with large birefringence Δ n ( n z - n x ) of 0.1522 at 1064 nm and 0.1720 at 532 nm. Based on the measured refractive indices, the phase-matching conditions for second-harmonic generation (SHG) have been calculated, and SHG devices have further been fabricated along the calculated type I and type II phase-matching directions of (θ = 39.0°, φ = 3.8°) and (θ =53.8°, φ = 1.3°). Laser experiments of extra-cavity frequency doubling have been performed on these NVIO devices. It has been confirmed that the effective SHG conversion from 1064 to 532 nm could be achieved with an energy conversion efficiency of 8.1%. Our work demonstrates that large-sized NVIO crystals are promising in the frequency-doubling application.

A new phase-matchable nonlinear-optical material, Na 3 Ti 3 O 3 (SeO 3 ) 4 F, has been achieved by a facile hydrothermal reaction. The anionic skeleton displays a honeycombed 3D structure with Ti 6 Se 6 12-member polyhedral ring tunnels along the c axis. Na 3 Ti 3 O 3 (SeO 3 ) 4 F presents a strong second-harmonic-generation (SHG) response of about 6 × KDP, which is twice that of its isostructural Ag compound. Interestingly, the band gap of Na 3 Ti 3 O 3 (SeO 3 ) 4 F is also broader than that of the isomorph. Also, the powder laser-induced damage threshold of Na 3 Ti 3 O 3 (SeO 3 ) 4 F is even 5.5 times larger than that of Ag 3 Ti 3 O 3 (SeO 3 ) 4 F. Theoretical calculations revealed that the fully filled Ag 4d and empty Ag 5s states have made the difference in the band gap and SHG response of the two isostructural compounds. Our work has provided a practical way of improving the SHG efficiency and band gap simultaneously, which is usually considered to be a pair of negatively correlated parameters.

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO 3 )(NO 3 ), was successfully synthesized by traditional solid state reactions. This compound crystallizes in the polar space group of Pca2 1 , and its structure features a novel 2D layered structure consisting of 1D lead nitrate chains and 2D cadmium selenite layers. PbCdF(SeO 3 )(NO 3 ) exhibits a phase-matchable SHG efficiency of about 2.6 times that of KDP and a wide band gap of 4.42 eV. Its laser damage threshold was measured to be 135.6 MW/cm 2 , which is comparative to that of the reported Li 7 (TeO 3 ) 3 F with a short ultraviolet cutoff edge. Theoretical calculation confirmed that the synergistic effects of all the four functional units make PbCdF(SeO 3 )(NO 3 ) a remarkable SHG material.

Noncentrosymmetric (NCS) mixed-metal chalcogenides have attracted significant attention lately because of their structural multiplicities, strong second-harmonic-generation (SHG) efficiencies ( d ij ) and large laser-induced damage thresholds (LIDTs), which make them promising nonlinear-optical (NLO) materials in mid- and far-IR (MFIR) applications. In this work, a ternary mixed-metal material, Cd 4 GeS 6 , has been synthesized by reacting CdS with GeS 2 via a solid-state method at 1273 K. It exhibits a unique tetrahedral-stacking NCS framework structure consisting of two types of [Cd 2 S 7 ] asymmetric groups and dispersed GeS 4 tetrahedra. Remarkably, Cd 4 GeS 6 shows type-I phase-matching ability and achieves a desired balance between strong d ij (about 1.1AgGaS 2 ) and large LIDT (about 3.6AgGaS 2 ), demonstrating that this material satisfies the essential requirements as a promising MFIR NLO candidate. Moreover, theoretical calculations were performed for a better understanding of the structure-property relationships.

Partial substitution of iodate anions in La(IO 3 ) 3 by OH - or NO 3 - anion led to acentric La 3 (IO 3 ) 8 (OH) and chiral La(IO 3 ) 2 (NO 3 ). The structure of La 3 (IO 3 ) 8 (OH) can be seen as a complex three-dimensional (3D) network composed of two-dimensional [La 3 (IO 3 ) 2 (OH)] 6+ cationic layers that are further bridged by remaining iodate anions, or alternatively as a 3D network composed of one-dimensional [La 3 (IO 3 ) 6 (OH)] 2+ cationic columns being further interconnected by additional iodate anions, while the structure of La(IO 3 ) 2 (NO 3 ) can be seen as a novel 3D structure with planar NO 3 groups serving as linkage between the [La 3 (IO 3 ) 6 ] 3+ triple layers. Compared to La(IO 3 ) 3 , both compounds show considerably wide band gaps and enhanced thermal stability. La(IO 3 ) 2 (NO 3 ) shows a moderate second harmonic generation (SHG) response of ∼0.6 times that of KDP (KH 2 PO 4 ), a wide band gap of 4.23 eV, and a high LDT value (22 × AgGaS 2 ). Optical property measurements, thermal analysis, as well as theoretical calculations on SHG origin, were performed. It can be deduced that partial substitution of iodate anions can be a facile route to design new noncentrosymmetric metal iodates with novel structure and potential application.