A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced ...damage threshold (LIDT). Herein we report the preparation of a new Ga2Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga2Se3 phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.
A simple but perfect case: A new phase of gallium selenides (δ‐Ga2Se3) has been obtained via solid‐state reactions. δ‐Ga2Se3 is phase‐matchable with large second harmonic generation (SHG) responses, high laser‐induced damage thresholds (LIDTs), and wide transparent range of 0.59–25 μm. These properties are all required for the application of NLO materials with high‐power lasers.
A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A ...salt‐inclusion chalcogenide (SIC), LiLiCs2ClGa3S6 (1), was prepared that presents a nanosized tunnel framework constructed from monotype chalcogenide tetrahedra. Highly oriented covalent GaS4 tetrahedra in the host lead to a moderate second harmonic generation response (0.7 AgGaS2), and ionic guests effectively broaden the band gap to the widest value (4.18 eV) among all IR NLO chalcogenides, thereby achieving a remarkable balance between NLO efficiency and band gap.
The salt‐inclusion chalcogenide LiLiCs2ClGa3S6 is presented, which features a 3D framework composed of Ga3S6 nanosized tunnels. Introduction of an ionic guest to the covalent chalcogenide host produces a material with a moderate nonlinear optical (NLO) coefficient and an ultrawide band gap (Eg). These characteristics are promising for the development of infrared (IR) NLO materials.
Extending photoresponse ranges of semiconductors to the entire ultraviolet-visible (UV)-shortwave near-infrared (SWIR) region (ca. 200-3000 nm) is highly desirable to reduce complexity and cost of ...photodetectors or to promote power conversion efficiency of solar cells. The observed up limit of photoresponse for organic-based semiconductors is about 1800 nm, far from covering the UV-SWIR region. Here we develop a cyanide-bridged layer-directed intercalation approach and obtain a series of two viologen-based 2D semiconductors with multispectral photoresponse. In these compounds, infinitely π-stacked redox-active N-methyl bipyridinium cations with near-planar structures are sandwiched by cyanide-bridged Mn
-Fe
or Zn
-Fe
layers. Radical-π interactions among the infinitely π-stacked N-methyl bipyridinium components favor the extension of absorption range. Both semiconductors show light/thermo-induced color change with the formation of stable radicals. They have intrinsic photocurrent response in the range of at least 355-2400 nm, which exceeds all reported values for known single-component organic-based semiconductors.
•Recent researches on NLO crystals with mixed-anions are overviewed.•NLO crystals with mixed-anions demonstrate rich structures.•Different functional moieties function differently for the NLO ...properties.•The structure-NLO property relationships are addressed.•Several future considerations have been supposed.
Crystals with mixed anions refer to inorganic salts containing at least two types of anions or anionic groups, and these anions can be Q2− (Q = O, S, Se, Te) and X− (X = F, Cl, Br, I), and anionic groups include various B–O groups, (OH)−, (IO3)−, (CO3)2−, (SiO4)4−, (NO3)3− and (PO4)3−. Recently, in view of the insufficiency and strong requirements of second-order nonlinear optical (NLO) crystals, especially ones in the deep ultraviolet (DUV) and middle and far-infrared (MFIR) regions, the study of NLO crystals have received intensive interest from researchers. For a NLO crystal candidate, desirable properties include large NLO coefficients, high laser-induced damage threshold values, phase matchabilities and wide transparent windows. The availability of the former two properties is especially problematic since the structural factor influences them in reverse order. To balance them, it is necessary to introduce different anions into the structure to induce them to function differently. Under the guidance of anionic group theory and the functional moiety concept, many NLO crystals with mixed anions have been obtained. However, to date, a systematic survey of this topic has not been carried out. In this review, recently reported NLO crystals with mixed anions are summarized, the contents of which are mainly focused on their crystal structures and NLO behaviors, together with the relationship between these two aspects. It is hoped that this work will provide a useful perspective on the most promising NLO candidates.
In contrast to anionic group theory of nonlinear optical (NLO) materials that second‐harmonic generation (SHG) responses mainly originate from anionic groups, structural regulation on the cationic ...groups of salt‐inclusion chalcogenides (SICs) is performed to make them also contribute to the NLO effects. Herein, the stereochemically active lone–electron‐pair Pb2+ cation is first introduced to the cationic groups of NLO SICs, and the resultant K2PbXGa7S12 (X = Cl, Br, I) are isolated via solid‐state method. The features of their three‐dimensional structures comprise highly oriented Ga7S123− and K2PbX3+ frameworks derived from AgGaS2, which display the largest phase‐matching SHG intensities (2.5−2.7 × AgGaS2 @1800 nm) among all SICs. Concurrently, three compounds manifest band gap values of 2.54, 2.49, and 2.41 eV (exceeding the criterion of 2.33 eV), which can avoid two‐photon absorption under the fundamental laser of 1064 nm, along with the relatively low anisotropy of thermal expansion coefficients, leading to improved laser‐induced damage thresholds (LIDTs) values of 2.3, 3.8, and 4.0 times that of AgGaS2. In addition, the density of states and SHG coefficient calculations demonstrate that the Pb2+ cations narrow the band gaps and benefit SHG responses.
By introducing stereochemically active lone–electron‐pair cations in the cationic groups of salt‐inclusion chalcogenides (SICs), three compounds K2PbXGa7S12 (X = Cl, Br, I) are successfully obtained, which display the highest phase‐matching nonlinear optical (NLO) responses in reported SICs and suitable band gaps exceeding 2.33 eV to avoid two‐photon absorption at 1064 nm.
The typical chalcopyrite AgGaQ2 (Q = S, Se) are commercial infrared (IR) second‐order nonlinear optical (NLO) materials; however, they suffer from unexpected laser‐induced damage thresholds (LIDTs) ...primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by SZn4S12 + S4Zn13S24 + 11ZnS4 ⇒ MS12+ M4ClS24 + 11GaS4, in which the covalent SxZny units in the diamond‐like sphalerite ZnS are synergistically replaced by cationic MxCly units, resulting in two novel salt‐inclusion sulfides, MM4ClGa11S20 (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS2, facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS2@1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second‐harmonic generation intensities (0.84 and 0.78 × AgGaS2@2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond‐like structures to provide a feasible chemical design insight for constructing high‐performance NLO materials.
What sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, offers two excellent infrared nonlinear optical materials, which provides a feasible chemical design insight for constructing high‐performance nonlinear optical materials.
Exploring nonlinear optical (NLO) functional motifs (FM, the structural origin of NLO efficiency) is vital for the rational design of NLO materials. Normal spectrum techniques applied in studying ...photon exciting materials are invalid for NLO materials, in which electrons are not excited substantially but only distorted under laser. A general strategy of determining NLO FM is proposed by comparative studies of experimental electron density (ED) without and under the laser. The in situ experimental ED and wavefunction of typical NLO material LiB3O5 (LBO) under dark and 360 and 1064 nm lasers are investigated. Compared with the initial state under dark, the ED of B3O5− unit at functional states under laser irradiation exhibits remarkable changes of topological atomic and bond properties, confirming the NLO FM being B3O5−. The work extracts for the first time the FM of a NLO material experimentally and highlights the crucial role of in situ ED analysis in studying NLO mechanisms.
A general strategy of determining nonlinear optical (NLO) functional motif (FM) is proposed by comparative studies of experimental electron density (ED) without and under the laser. In situ ED analysis is firstly adopted for an NLO material with typical LiB3O5 as an example. The work extracts the FM of a NLO material experimentally and highlights the crucial role of in situ ED analysis in studying NLO mechanisms.
To circumvent the incompatibility between large nonlinear optical (NLO) efficiencies and high laser-induced damage thresholds (LIDTs) in mid-infrared NLO materials, a new strategy for designing ...materials with both excellent properties is proposed. This strategy involves narrowing the band gap for large NLO efficiencies and reducing the thermal effect for a high LIDT. To support these proposals, a series of isostructural chalcogenides with various tetrahedral center cations, Na
Ga
MQ
(M = Ge, Sn; Q = S, Se), were synthesized and studied in detail. Compared with the benchmark AGS, these chalcogenides exhibit significantly narrower band gaps (1.56-1.73 eV, AGS: 2.62 eV) and high NLO efficiencies (1.6-3.9 times that of AGS at 1910 nm), and also outstanding LIDTs of 8.5-13.3 × those of AGS for potential high-power applications, which are contrary to the conventional band gap view but can be attributed to their small thermal expansion anisotropy, surmounting the NLO-LIDT incompatibility. These results shed light on the search for practical IR NLO materials with excellent performance not restricted by NLO-LIDT incompatibility.
Chalcohalides not only keep the balance between the nonlinear optical (NLO) coefficient and wide band gap, but also provide a promising solution to achieve sufficient birefringence for phase‐matching ...ability in NLO crystals. In this study, a novel chalcohalide, Cs4Zn5P6S18I2 (1) is successfully synthesized, by incorporating the highly electropositive Cs and the large electronegative I element into the zinc thiophosphate. Its 3D open framework features an edge‐shared by distorted ZnS4, ethanol‐like P2S6, and unusual ZnS2I2 polyhedrons, which is inconsistent with the soft‐hard‐acids‐bases theory. Remarkably, compound 1 simultaneously exhibits the large second‐harmonic generation (SHG, 1.1×AgGaS2, @1.3 µm) and a wide band gap (3.75 eV) toward a high laser‐induced damage threshold (16.7×AgGaS2, @1.06 µm), satisfying the rigorous requirements for a prominent infrared NLO material with concurrent SHG intensity (≥0.5×AGS) and band gap (≥3.5 eV). Moreover, to the best of the knowledge, the experimental result shows that phase 1 has the largest birefringence (0.108, @546 nm) in chalcohalide and meets phase‐matching behavior demand originating from the polarizable anisotropy of NLO‐functional motifs. This finding may provide great opportunities for designing birefringent chalcohalides.
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![[K2PbX][Ga7S12] (X = Cl, Br...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2198-3844/small "[K2PbX][Ga7S12] (X = Cl, Br, I): The First Lead‐Containing Cationic Moieties with Ultrahigh Second‐Harmonic Generation and Band Gaps Exceeding the Criterion of 2.33 eV")
![[ABa 2 Cl][Ga 4 S 8 ] (A = ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0002-7863/small "[ABa 2 Cl][Ga 4 S 8 ] (A = Rb, Cs): Wide-Spectrum Nonlinear Optical Materials Obtained by Polycation-Substitution-Induced Nonlinear Optical (NLO)-Functional Motif Ordering")
