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Thioborates are considered new potential mid-infrared nonlinear optical (NLO) crystals with wide band gaps and large second-harmonic generation (SHG) coefficients. Despite the fact that many rare-earth thioborates are structurally non-centrosymmetric, their SHG properties have only been studied very recently and their mid-infrared (Mid-IR) nonlinear optical properties have not yet been studied. In this work, we provide a new synthetic route for LaBS3 (LBS) by solid state reactions of La2S3, B and S with Li2S as flux, and we further study its thermal and optical properties, and theoretically explore the origin of its IR nonlinear optical properties by DFT calculations. Remarkably, LBS possesses balanced properties required for a good Mid-IR NLO crystal, a large SHG effect (1.2 × AgGaS2@2.05 μm – the largest among all known ortho-thioborates), a high laser induced-damage threshold (14 times of AgGaS2), a wide band gap (3.18 eV), a wide infrared transmission range (0.35–25 μm) and high thermal stability. Theoretical calculations suggest that its large SHG effect originates from the synergy effects of the π-conjugated [BS3]3− anions (41.82%) and the [LaS9]15− groups (58.18%). [ABSTRACT FROM AUTHOR]

The introduction of coordination polyhedra containing stereo-chemically active lone pairs into the chalcogenide structures is beneficial for realizing centric-to-acentric structural transformation and further enhancing the second-harmonic generation (SHG) efficiency (dij) and the birefringence (Δn) for IR nonlinear optical (NLO) applications; however, this has been rarely reported. Herein, non-centrosymmetric (NCS) arsenates M2As2Q5 (M = Ba, Pb; Q = S, Se) have been screened out by combined experiments and theoretical calculations as a new source of IR NLO materials. Interestingly, they feature unique zero-dimensional structures containing diverse types of discrete As-based coordination polyhedra with M2+ cations located among them, which is discovered for the first time in the IR-NLO chalcogenides. More significantly, they all exhibit multiple key NLO parameters for practical applications in the IR region, including wide phase-matching ranges (>950–1370 nm), remarkable dij (1.0–2.7 × AgGaS2) and large laser-induced damage thresholds (LIDTs = 6.8–12.4 × AgGaS2). Theoretical studies demonstrate that the discrete As-based coordination polyhedra play a critical role in the linear optical and NLO responses of the title compounds. We believe that this work can not only enrich the diversity of NLO-active groups, but also provide a new choice for material design in NCS chalcogenides. [ABSTRACT FROM AUTHOR]

It is highly desirable but challenging to design and synthesize novel non-centrosymmetric (NCS) metal–organic frameworks (MOFs) with excellent nonlinear optical (NLO) properties. And the origin of their NLO responses remains vague. Herein, a novel 1D Zn-based MOF with unique zigzag helical chains, [Zn(bct)(H2O)2] (MOF-FJ1), has been prepared from achiral precursors. It crystallizes in an NCS space group P212121 (no. 19) and is found to be a remarkable NLO material with a strong second-harmonic-generation (SHG) response (3.5 × commercial KH2PO4 (KDP)) and high laser-induced damage threshold (1.6 × commercial KDP). Moreover, theoretical calculations based on the length-gauge formalism are discussed to unveil a deepened cognition of the structure–property relationship, providing theoretical insight into the origin of the NLO response. [ABSTRACT FROM AUTHOR]