Anhydrous Aluminum Iodate: Strong Second Harmonic Generation Effect Contributed by Unbonded and Antibonding Orbitals

Exploring materials that balance the second harmonic generation (SHG) effect and laser-induced damage threshold (LIDT) is the frontier of nonlinear optical (NLO) crystal research at present. In this work, the NLO property of anhydrous aluminum iodate is extensively explored and discussed first. It exhibits a strong SHG intensity of 18.3 × KH2PO4 (KDP) and a high-powder LIDT of 1.4 × KDP at 1064 nm. Combining experimental and theoretical studies at the atomic level and electronic levels, it is found that the cations in the structure are replaced by cations with small radius and high valence, enabling the production of materials with large SHG responses. Unbonded and antibonding orbitals play a crucial positive role in the SHG response of the structure, whereas bonding orbitals produce a large negative contribution. This provides a scarce example of materials in which bonding orbitals make significant negative contributions

Designing Sulfide Borate as a Novel Type of Second-Order Nonlinear-Optical Material

Designing second-order nonlinear-optical (NLO) materials with new structures is an attractive topic. Here, a novel type of sulfide borate, Eu2B5O9S, and one of its derivatives combining S2–, I–, and borate anions in one structure (three in one), viz., Eu4.5(B5O9)2SI, are designed and synthesized with a high-temperature solid-state method. They crystallize in the noncentrosymmetric space group Pnn2. As the first sulfide borate being NLO-active, Eu4.5(B5O9)2SI demonstrates good NLO behavior, namely, a moderate powder NLO response of ca. 0.5 times and a high laser-induced damage threshold (LIDT) of ca. 15 times those of AgGaS2, and is phase-matchable. The design strategy and experimental results are verified and explained by density functional theory calculations

Sm₃S₃BO₃: The First Sulfide Borate without S–O and B–S Bonds

An unprecedented quaternary sulfide borate, Sm₃S₃BO₃ (<b>1</b>), was obtained via a high-temperature solid-state synthesis method. It crystallizes in the triclinic space group <i>P</i>1̅, and its 3D structure features a 2D (Sm₂S₂)_∞ wrinkled layer and a 1D (SmS)_∞ ladderlike chain bridged by trigonal-planar (BO₃)^3– through Sm–O bonds, demonstrating the first sulfide borate without S–O and B–S bonds. Its optical energy gap is measured to be around 2.5 eV and verified by electronic structure calculation

Structural Chemistry and Excellent Nonlinear Optical Properties of a Series of Ternary Selenides Ga_<i>x</i>In_2–<i>x</i>Se₃

Novel nonlinear optical (NLO) materials possessing simple chemical compositions and facile syntheses are competitive when considering their practical application. Here, a series of ternary selenides GaxIn2–xSe3 (x = 0.07, 0.38, 0.45, and 0.81) that crystallize in a chiral P65 structure are obtained by melting Ga, In, and Se elements. Their three-dimensional structures are built by (Ga/In)­Se4 tetrahedra and InSe5 trigonal bipyramids. The hexagonal modification’s phase stability is analyzed by energy calculation, and their optical band gaps are determined to be 1.72–1.99 eV. They exhibit large NLO responses that are 1.41–1.64 times that of the benchmark AgGaS2. The results of density functional theory calculations suggest that introduction of Ga onto the In site in (InSe4)5– units can form a deformed tetrahedron with more distortion in the structure, and the (InSe5)7– units contribute a large amount of birefringence to the structure. This work is the first to investigate the ternary chalcogenides M2Q3 (M = Ga or In; Q = S or Se) as new types of infrared NLO crystals with excellent performances, which will stimulate more interest in those possessing simple compositions and outstanding performances

Sn₂Ga₂S₅: A Type of IR Nonlinear-Optical Material

The deficiency of nonlinear-optical (NLO) materials in the IR region inspires strong research interest in this field. Here, Sn2Ga2S5 (1), crystallizing in the orthorhombic Pna21 space group, demonstrates obvious NLO activity, around a maximum of 1.6 times that of AgGaS2 and a strong laser-induced damage threshold of 9.7 times that of AGS. 1 represents the first NLO-active compound in the MII2MIII2Q5 (MII = divalent Ca, Sr, Ba, Pb, Sn, and Eu; MIII = B, Al, Ga, and In; Q = S and Se) family. The NLO performances of 1 are systematically studied experimentally and theoretically

Balanced Second-Order Nonlinear Optical Properties of Adducts CHI₃·(S₈)₃ and AsI₃·(S₈)₃: A Systematic Survey

Two isostructural adducts CHI3·(S8)3 (1) and AsI3·(S8)3 (2) are synthesized by a simple solution method. Both of them crystallize in noncentrosymmetric R3m, featuring van der Waals interaction linked CHI3 tetrahedra or SbI3 trigonal pyramids with crown-like S8 molecules. Both 1 and 2 show strong SHG responses and phase matchability under either 1.064 or 2.1 μm. The results of DFT calculations indicate that the electron transfer happens from S-3p to I-5p orbitals, and both of them demonstrate indirect band gaps. The NLO effects of 1 and 2 are almost fully contributed from the CHI3 or AsI3 units. Compared with AgGaS2, their powder laser damage thresholds are ca. 15 and 51 times higher