Strong Second Harmonic Generation Response Research Articles

SbO(OH)2(IO3): The First Polar Sb5+-Iodate with a Strong Second-Harmonic Generation Response and a Wide Bandgap.

Widening the bandgaps while maintaining a strong second harmonic generation response has always been a research hotspot in the field of nonlinear optical iodate materials. A strategy involving covalent bonding is proposed that leverages the high valent later main group cation to construct iodates with predominantly covalent interactions. By using BiO(IO3) as a template, the first Sb5+-containing polar iodate, SbO(OH)2(IO3) is successfully isolated. The introduction of the two hydroxide anions led to the reduction of layered BiO(IO3) into 1D SbO(OH)2(IO3) in which two corner-sharing SbO4(OH)2 octahedra are further bridged by an iodate group. The covalently bonded [SbO(OH)2]+ chains and the optimal packing fashion of the asymmetric IO3 - groups generate a very strong second harmonic generation signal of 14 times that of KH2PO4. Furthermore, SbO(OH)2(IO3) exhibits a wide bandgap of 4.14eV and a high laser induced damage threshold [27.9 × AgGaS2, 0.2 × KH2PO4 (10ns, 10Hz)].

Designing a 2D van der waals oxide with lone-pair electrons as chemical scissor

Abstract 2D van der Waals (vdW) materials are known for their intriguing physical properties, but their rational design and synthesis remain a great challenge for chemists. In this work, we successfully synthesized a new non-centrosymmetric oxide, i.e. InSbMoO6, with Sb3+ lone-pair electrons serving as chemical scissor to generate its 2D vdW crystal structure. Monolayer and few-layer InSbMoO6 flakes are readily obtained via facile mechanical exfoliation. They exhibit strong second-harmonic generation (SHG) response with an effective second-order nonlinear optical susceptibility $\chi _{{\rm{eff}}}^{{\rm{(2)}}}\ $of 32.4 pm·V−1. Meanwhile, the SHG response is in-plane anisotropic and directly proportional to the layer thickness, independent of layer parity. In addition, the InSbMoO6 flakes exhibit excellent thermal and atmospheric stability, along with pronounced anisotropy in Raman spectroscopy. This work implies that using lone-pair electrons as chemical scissor is an effective strategy for designing and synthesizing new 2D vdW materials for integrated photonic applications.

Carbonatoperoxovanadates with Strong Second-Harmonic Generation: Insights from First-Principles Calculations on Anisotropic Structures and Optical Parameters.

Carbonatoperoxovanadates are considered as promising functional materials in optoelectronic devices due to their excellent optical properties, particularly strong second-harmonic generation (SHG) response. However, the relationship between their geometric structures and optical properties remains unclear. Herein, the structural, electronic, and optical properties of carbonatoperoxovanadates A3VO(O2)2CO3 (A=K, Rb, and Cs) were investigated using first-principles calculation. Results suggest that high density and parallel arrangement of nonlinear optical active [VO(O2)2CO3] units are conducive to generating large SHG response in A3[V(O2)2O]CO3. Optical anisotropy was observed. Birefringence values for A3[V(O2)2O]CO3 were comparable to those of commonly used infrared nonlinear optical materials. Specifically, results of tiny optical characteristics (local dipole moments, HUMO-LUMO gap, polarizability anisotropy, and hyperpolarizability) indicate that asymmetry [VO(O2)2CO3] is an excellent nonlinear optical active functional unit, owing to the synergistic effect between its non-centrosymmetric nonlinear optical elements. This study elucidates the structure-property relationship of carbonatoperoxovanadates, offering valuable insights for designing novel high-performance SHG materials.

Toward Strong UV-Vis-NIR Second-Harmonic Generation by Dimensionality Engineering of Zinc Thiocyanates.

The precise modulation of the spatial orientations and connection modes of primitives is vital for certain critically important optical functions for nonlinear optical (NLO) materials (specifically, second-harmonic generation (SHG) and optical bandgap); however, we are yet to achieve a sufficient level of control for the designed construction of efficient broadband NLO materials. Exploiting the changes in microscopic polarization that may result from dimensional increase, we propose herein a zero-dimensional (0D)-to-three-dimensional (3D) dimensionality-increase strategy to realize strong broadband SHG responses for the first time. The novel 3D pseudo diamond-like Zn(SCN)2 has been synthesized by removing SHG-inactive [NH4]+ counter cations and H2O molecules that are located between the adjacent discrete [Zn(SCN)4] building blocks within the 0D (NH4)2Zn(SCN)4·3H2O. The 0D-to-3D dimensionality engineering, proceeding from (NH4)2Zn(SCN)4·3H2O to Zn(SCN)2, results in significantly enhanced SHG responses and efficient broadband activity (8 × KH2PO4 @ 1064 nm, 4.18 eV bandgap for the former c.f. 2 × β-BaB2O4 @ 380 nm, 30 × KH2PO4 @ 1064 nm, 2 × KTiOPO4 @ 2100 nm, 4.78 eV bandgap for the latter) from the UV to the NIR regions (SHG@300-1050 nm). Theoretical calculations and crystal structure analyses reveal that the coordination-bond-connected [Zn(SCN)4] building blocks within the diamond-like structure of Zn(SCN)2 are responsible for its giant broadband SHG responses.

Polar Thiazole Derivative-Induced Second Harmonic Response in Hybrid Bismuth Chlorate with Reversible Photochromism.

Inorganic-organic hybrid bismuth halides demonstrate great prospect in the field of second-order nonlinear optical (NLO) crystals because the ns2 electron on Bi(III) could lead to large molecular polarization and high second harmonic generation (SHG) coefficient on a noncentrosymmetric structure. However, researchers cannot yet control the effective arrangements of the bismuth halide functional motif, which results in SHG-active hybrid bismuth halides being rare. Herein, thiazole derivatives with a polar donor-π-acceptor system are designed to explore hybrid bismuth halide NLO crystals. The protonated 2-(4-hydroxyphenyl) thiazole (denoted as hpt) interacts with the (BiCl6) motif via H···Cl hydrogen bonds to prevent antiparallel arrangements, which therefore enhance the NLO property. (Hhpt)3[BiCl6] crystallizes in the monoclinic polar P21 space group, which exhibits a strong SHG response and reversible photochromic behavior. Structural analysis and theory calculations reveal that the synergistic effect between the polar thiazole derivative and the distorted inorganic [BiCl6]3- motif is responsible for the SHG response. This is the first report of polar thiazole derivative-induced SHG-active hybrid bismuth halide coupled with reversible photochromism.

Achieving the Birefringence Optimization by Methyl Modulation in Organic Nonlinear Optical Crystals

AbstractNon‐centrosymmetric organics are promising nonlinear optical (NLO) candidates, which always exhibit a short UV absorption cutoff edge, and a strong second harmonic generation (SHG) response, but an overlarge birefringence. Here, in order to optimize the birefringence, the methyl modulation of π‐conjugated organic planar units is proposed and implemented with the urea structure as a template. Thus, N‐methylurea and N,N'‐dimethylurea crystals are obtained by partially replacing hydrogen atoms with methyl groups. This replacement reduces hydrogen donors and weakens interchain hydrogen bonds, which facilitates the decreasing density and the parallel arrangement of π‐conjugated planar units. Hence, both N‐methylurea and N,N'‐dimethylurea crystals exhibit not only an optimized birefringence (N‐methylurea ≈0.099 and N,N'‐dimethylurea ≈0.072 at 546 nm) but also an enhanced SHG response (N‐methylurea ≈1.2 × β‐BaB2O4 and N,N'‐dimethylurea ≈1.9 × β‐BaB2O4), while maintaining a short UV absorption cutoff edge. Therefore, this work provides a novel strategy for the structural design and performance modulation of organic NLO crystals.

Harnessing complexity: Nonlinear optical phenomena in L-shapes, nanocrescents, and split-ring resonators.

We conduct systematic studies of the optical characteristics of plasmonic nanoparticles that exhibit C2v symmetry. In particular, we analyze three distinct geometric configurations: an L-type shape, a crescent, and a split-ring resonator shaped like the Greek letter π. Optical properties are examined using the finite-difference time-domain method. It is demonstrated that all three shapes exhibit two prominent plasmon modes associated with the two axes of symmetry. This is in addition to a wide range of resonances observed at high frequencies corresponding to quadrupole modes and peaks due to sharp corners. Next, to facilitate nonlinear analysis, we employ a semiclassical hydrodynamic model, where the electron pressure term is explicitly accounted for. This model goes beyond the standard Drude description and enables capturing nonlocal and nonlinear effects. Employing this model enables us to rigorously examine the second-order angular resolved nonlinear optical response of these nanoparticles in each of the three configurations. Two pumping regimes are considered, namely, continuous wave (CW) and pulsed excitations. For CW pumping, we explore the properties of the second harmonic generation (SHG). Polarization and angle-resolved SHG spectra are obtained, revealing strong dependence on the nanoparticle geometry and incident wave polarization. The C2v symmetry is shown to play a key role in determining the polarization states and selection rules of the SHG signal. For pulsed excitations, we discuss the phenomenon of broadband terahertz (THz) generation induced by the difference-frequency generation . It is shown that the THz emission spectra exhibit unique features attributed to the plasmonic resonances and symmetry of the nanoparticles. The polarization of the generated THz waves is also examined, revealing interesting patterns tied to the nanoparticle geometry. To gain deeper insight, we propose an analytical theory that agrees very well with the numerical experiments. The theory shows that the physical origin of the THz radiation is the mixing of various frequency components of the fundamental pulse by the second-order nonlinear susceptibility. An expression for the far-field THz intensity is derived in terms of the incident pulse parameters and the nonlinear response tensor of the nanoparticle. The results presented in this work offer new insights into the linear and nonlinear optical properties of nanoparticles with C2v symmetry. The demonstrated strong SHG response and efficient broadband THz generation hold great promise for applications in nonlinear spectroscopy, nanophotonics, and optoelectronics. The proposed theoretical framework also provides a valuable tool for understanding and predicting the nonlinear behavior of other related nanostructures.

Remarkable Second Harmonic Generation Response in (C5H6NO)+(CH3SO3)−: Unraveling the Role of Hydrogen Bond in Thermal Driven Nonlinear Optical Switch

AbstractHeat‐activated second harmonic generation (SHG) switching materials are gaining interest for their ability to switch between SHG on and off states, offering potential in optoelectronic applications. The novel nonlinear optical (NLO) switch, (C5H6NO)+(CH3SO3)− (4‐hydroxypyridinium methylsulfonate, 4HPMS), is a near‐room‐temperature thermal driven material with a strong SHG response (3.3 × KDP), making it one of the most potent heat‐stimulated NLO switches. It offers excellent contrast of 13 and a high laser‐induced damage threshold (2.5 × KDP), with reversibility > 5 cycles. At 73 °C, 4HPMS transitions from the noncentrosymmetric Pna21 room temperature phase (RTP) to the centrosymmetric P21/c phase, caused by the rotation of the (C5H6NO)+ and (CH3SO3)− due to partially thermal breaking of intermolecular hydrogen bonds. The reverse phase change exhibits a large 50 °C thermal hysteresis. Density functional theory (DFT) calculations show that (C5H6NO)+ primarily dictates both the SHG coefficient (dij) and birefringence (▵n(Zeiss) = 0.216 vs ▵n(cal.) = 0.202 at 546 nm; Δn(Immersion) = 0.210 vs ▵n(cal.) = 0.198 at 589.3 nm), while the band gap (Eg) is influenced synergistically by (C5H6NO)+ and (CH3SO3)−. Additionally, 4HPMS‐RTP also exhibits mechanochromism upon grinding as well as an aggregation‐enhanced emission in a mixture of acetone and water.

La3Ga5M0.5Sn0.5O14, (M = Ge, Si): Design and Synthesis of Two Langasite Nonlinear Optical Materials with Large Second Harmonic Generation and Birefringence Induced by Distorted (Sn/M)O6 Octahedra.

Nonlinear optical (NLO) coherent light sources are widely applied in many areas of science and technology. As the core medium, the NLO material is required to have a wide transparent range, a large NLO response, and a high laser damaged threshold (LDT). It is common knowledge that langasite (La3Ga5SiO14, LGS) crystal has an underdeveloped second-harmonic generation (SHG) coefficient and a small birefringence, which seriously restrict its application in the NLO field, despite that it has a broad transmittance spectrum and a moderate LDT. Herein, we have successfully obtained novel langasite NLO crystals LGSS (La3Ga5Si0.5Sn0.5O14) and LGGS (La3Ga5Ge0.5Sn0.5O14), with short UV absorption edges of 209 and 212 nm, respectively. Incorporating heavy ions Sn4+ into the structure, a distorted BO6 octahedron was adjusted by the radius difference between Sn4+ and Si4+/Ge4+, which caused the strong SHG responses in LGSS (∼10.77 × KDP) and LGGS (∼9.23 × KDP) and increased birefringences of 0.034 and 0.025, respectively. Besides, they also had large energy band gaps (4.95 eV for LGSS, and 4.93 eV for LGGS), which allowed high LDTs with LGSS of 1.3 GW/cm2 and LGGS of 813 MW/cm2. This work demonstrates a new strategy to enhance SHG responses and birefringence for existing NLO materials and enriches langasite family crystals.

A3Sc(SO4)3 (A = K, Rb, Cs): Three Deep‐Ultraviolet Transparent Alkali‐Scandium Sulfates with Strong Second‐Harmonic Generation Response and High Thermal Stability

AbstractNonlinear optical (NLO) crystals that have the capability of achieving tunable lasers through frequency conversion are of great importance in solid‐state lasers. Herein, three new deep‐UV transparent alkali‐scandium sulfates with strong second‐harmonic generation (SHG) response and high thermal stability, A3Sc(SO4)3 (A = K, Rb, Cs), are successfully obtained. It is interesting that the slightly distorted [ScO6] octahedrons are in an ordered/oriented arrangement, which is in favor of the generation of SHG response. Especially, K3Sc(SO4)3 not only exhibits a strong phase‐matching SHG response of 1.6 × KDP, a short deep‐ultraviolet (deep‐UV) cutoff edge of 190 nm, a wide transparent window covering from the deep‐UV region to mid IR, a high laser‐induced damage threshold of 165 MW cm−2 and easy growth of large single crystal, but also behaves thermal stable up to 900 °C under an air atmosphere. Crystal structures and theoretical calculations reveal that their strong SHG responses mainly stem from the slightly distorted [ScO6] octahedron. This study highlights A3Sc(SO4)3 (A = K, Rb, Cs) as promising deep‐UV transparent NLO crystals and offers a new approach for the pursuit of high‐performance NLO crystals.

Second Harmonic Generation in β-K2TeW3O12: An Acentric Crystal Designed from Centric Phase via Pressure Modulation.

The latent value of nonlinear optical (NLO) crystals applied in solid-state laser equipment necessitates the development of applicable strategies for constructing noncentrosymmetric (NCS) crystals. By modulating the synthetic temperature and pressure to achieve the rearrangement of [TeO3]2- groups, a new NCS tellurium tungstate, β-K2TeW3O12 (β-KTW), with a strong second harmonic generation (SHG) response was synthesized based on its centrosymmetric polymorphic phase α-K2TeW3O12 (α-KTW). Computational calculation reveals that the large SHG response of β-KTW (15 × KH2PO4@1064 and 1.5 × KTiOPO4@1950 nm) could be attributed to the uniform arrangement of the NLO-active [TeO3]2- and [WO6]6- groups. β-KTW also exhibits enlarged birefringence (0.196@1064 nm) and a high laser damage threshold (42.3 MW cm-2), showing great potential as a nonlinear crystalline material. This work also provides a new route for the construction of NLO crystals based on centric structure, i.e., reverse pressure regulation.

Remarkable Second Harmonic Generation Response in (C5H6NO)+(CH3SO3)-: Unraveling the Role of Hydrogen Bond in Thermal Driven Nonlinear Optical Switch.

Heat-activated second harmonic generation (SHG) switching materials are gaining interest for their ability to switch between SHG on and off states, offering potential in optoelectronic applications. The novel nonlinear optical (NLO) switch, (C5H6NO)+(CH3SO3)- (4-hydroxypyridinium methylsulfonate, 4HPMS), is a near-room-temperature thermal driven material with a strong SHG response (3.3 × KDP), making it one of the most potent heat-stimulated NLO switches. It offers excellent contrast of 13 and a high laser-induced damage threshold (2.5 × KDP), with reversibility > 5 cycles. At 73 °C, 4HPMS transitions from the noncentrosymmetric Pna21 room temperature phase (RTP) to the centrosymmetric P21/c phase, caused by the rotation of the (C5H6NO)+ and (CH3SO3)- due to partially thermal breaking of intermolecular hydrogen bonds. The reverse phase change exhibits a large 50 °C thermal hysteresis. Density functional theory (DFT) calculations show that (C5H6NO)+ primarily dictates both the SHG coefficient (dij) and birefringence (▵n(Zeiss) = 0.216 vs ▵n(cal.) = 0.202 at 546 nm; Δn(Immersion) = 0.210 vs ▵n(cal.) = 0.198 at 589.3 nm), while the band gap (Eg) is influenced synergistically by (C5H6NO)+ and (CH3SO3)-. Additionally, 4HPMS-RTP also exhibits mechanochromism upon grinding as well as an aggregation-enhanced emission in a mixture of acetone and water.

Sr2HgGe2OS6: A Hg-Based Oxychalcogenide Infrared Nonlinear Optical Material Exhibiting Favorable Balance between a Large Band Gap and Strong Second Harmonic Generation Response.

Currently, oxychalcogenides with mixed-anion groups that integrate the property advantages of oxides (wide optical band gap) and chalcogenides [strong second harmonic generation (SHG) response] through chemical substitution engineering have attracted widespread interest and are considered to be important candidates for infrared (IR) nonlinear optical (NLO) materials. Herein, the first Hg-based oxychalcogenide Sr2HgGe2OS6 with mixed anion [GeOS3] units has been successfully synthesized through a spontaneous crystallization method, which exhibits a favorable balance between the strong SHG response (0.7 × AgGaS2) and large optical band gap (2.9 eV). In addition, Sr2HgGe2OS6 shows high laser-induced damage threshold (LIDT, 2.1 × AgGaS2) as well as phase-matching (PM) performance. Theoretical calculations indicate that the Sr2HgGe2OS6 encompasses large birefringence of 0.128@2090 nm (3.3 × AgGaS2) and its SHG density mainly comes from [HgS4] tetrahedra and [GeOS3] units. This work not only demonstrates that Sr2HgGe2OS6 is a promising IR NLO material but also provides new ideas for the exploration of Hg-based oxychalcogenide IR NLO materials.

A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb): Porous Crystals Constructed on [Pb3Cl5O6] Clusters with Comprehensive Nonlinear Optical Performance

AbstractNonlinear optical (NLO) crystals that can extend the frequency range of coherent light have significant applications in laser technology, semiconductor manufacturing, and lithography. Herein, two interesting NLO crystals, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb), are rationally obtained. Their porous structures are constructed on [Pb3Cl5O6] clusters that possess large hyperpolarizability and polarizability anisotropy, and are arranged in a parallel manner. Remarkably, A2Pb3[H2N(CH2COO)2]3Cl5 (A = K, Rb) exhibits comprehensive NLO performance, including strong phase‐matching second‐harmonic generation (SHG) response, the widest bandgap among lead oxychloride NLO crystals, larger laser damage threshold than 127 MW cm−2, suitable birefringence of 0.11@1064 nm, high thermal stability, non‐deliquescence, as well as facile crystal growth. Theoretical calculations and structural analysis demonstrate that their strong SHG response is predominantly originated from the [Pb3Cl5O6] cluster. This study will provide a unique method for the discovery of new interesting NLO crystals in future.

Rational Combination of π-Conjugated and Non-π-Conjugated Groups Achieving Strong Nonlinear Optical Response, Large Optical Anisotropy, and UV Light-Switchable Fluorescence.

Combining π-conjugated and non-π-conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non-π-conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π-conjugated [C4N3H6] groups. The resulting organic-inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546nm), and blue-violet and green fluorescence near 360 and 520nm, respectively. This work expands the methodology for creating new NLO crystals through organic-inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material.

Record Second-Harmonic Generation and Birefringence in an Ultraviolet Antimonate by Bond Engineering.

Oxides have attracted considerable attention owing to their potential for nonlinear optical (NLO) applications. Although significant progress has been achieved in optimizing the structural characteristics of primitives (corresponding to the simplest constituent groups, namely, cations/anions/neutral molecules) comprising the crystalline oxides, the role of the primitives' interaction in determining the resultant functional structure and optical properties has long been underappreciated and remains unclear. In this study, we employ a π-conjugated organic primitive confinement strategy to manipulate the interactions between primitives in antimonates and thereby significantly enhance the optical nonlinearity. Chemical bonds and relatively weak H-bonding interactions promote the formation of cis- and trans-Sb(III)-based dimer configurations in (C5H5NO)(Sb2OF4) (4-HPYSOF) and (C5H7N2)(Sb2F7) (4-APSF), respectively, resulting in very different second-harmonic generation (SHG) efficiencies and birefringences. In particular, 4-HPYSOF displays an exceptionally strong SHG response (12 × KH2PO4 at 1064 nm) and a large birefringence (0.513 at 546 nm) for a Sb(III)-based NLO oxide as well as a UV cutoff edge. Structural analyses and theoretical studies indicate that polarized ionic bond interactions facilitate the favorable arrangement of both the inorganic and organic primitives, thereby significantly enhancing the optical nonlinearity in 4-HPYSOF. Our findings shed new light on the intricate correlations between the interactions of primitives, inorganic primitive configuration, and SHG properties, and, more broadly, our approach provides a new perspective in the development of advanced NLO materials through the interatomic bond engineering of oxides.

Molecular Crystals Constructed by Polar Molecular Cages: A Promising System for Exploring High-performance Infrared Nonlinear Optical Crystals.

Polar molecular crystals, with their densely stacked polar nonlinear optical (NLO) active units, are favored for their large second harmonic generation (SHG) responses and birefringence. However, their potential for practical applications as Infrared (IR) NLO materials has historically been underappreciated due to the weak inter-molecular interaction forces that may compromise their physicochemical properties. In this study, we propose molecular crystals with polar molecular cages as a treasure-house for the development of superior IR NLO materials and a representative system, binary chalcogenide molecular crystals, composed of [P4 Sn ] (n=3-9) polar molecular cages, is introduced. These crystals may not only achieve wide band gap, large SHG response, and birefringence in a single structure, but also exhibit favorable physicochemical properties. We subsequently obtained a polar molecular crystal, α-P4 S5 , which demonstrated exceptional IR optical properties, including a strong SHG response (1.1×AGS), wide band gap (3.02 eV), large birefringence (0.134@2050 nm), and a broad transmission range (0.41-14.7 μm). Moreover, it showed excellent water resistance and hardness. These findings highlight the potential of polar molecular crystals as a promising platform for the development of high-performance IR NLO materials.

Molecular Crystals Constructed by Polar Molecular Cages: A Promising System for Exploring High‐performance Infrared Nonlinear Optical Crystals

AbstractPolar molecular crystals, with their densely stacked polar nonlinear optical (NLO) active units, are favored for their large second harmonic generation (SHG) responses and birefringence. However, their potential for practical applications as Infrared (IR) NLO materials has historically been underappreciated due to the weak inter‐molecular interaction forces that may compromise their physicochemical properties. In this study, we propose molecular crystals with polar molecular cages as a treasure‐house for the development of superior IR NLO materials and a representative system, binary chalcogenide molecular crystals, composed of [P4Sn] (n=3–9) polar molecular cages, is introduced. These crystals may not only achieve wide band gap, large SHG response, and birefringence in a single structure, but also exhibit favorable physicochemical properties. We subsequently obtained a polar molecular crystal, α‐P4S5, which demonstrated exceptional IR optical properties, including a strong SHG response (1.1×AGS), wide band gap (3.02 eV), large birefringence (0.134@2050 nm), and a broad transmission range (0.41–14.7 μm). Moreover, it showed excellent water resistance and hardness. These findings highlight the potential of polar molecular crystals as a promising platform for the development of high‐performance IR NLO materials.

Giant Optical Anisotropy in a Covalent Molybdenum Tellurite via Oxyanion Polymerization.

Large birefringence is a crucial but hard-to-achieve optical parameter that is a necessity for birefringent crystals in practical applications involving modulation of the polarization of light in modern opto-electronic areas. Herein, an oxyanion polymerization strategy that involves the combination of two different types of second-order Jahn-Teller distorted units is employed to realize giant anisotropy in a covalent molybdenum tellurite. Mo(H2O)Te2O7 (MTO) exhibits a record birefringence value for an inorganic UV-transparent oxide crystalline material of 0.528 @ 546nm, which is also significantly larger than those of all commercial birefringent crystals. MTO has a UV absorption edge of 366nm and displays a strong powder second-harmonic generation response of 5.4 times that of KH2PO4. The dominant roles of the condensed polytellurite oxyanions [Te8O20]8- in combination with the [MoO6]6- polyhedra in achieving the giant birefringence in MTO are clarified by structural analysis and first-principles calculations. The results suggest that polymerization of polarizability-anisotropic oxyanions may unlock the promise of birefringent crystals with exceptional birefringence.

In Situ Chiral Template Approach to Synthesize Homochiral Lead Iodides for Second‐Harmonic Generation

AbstractHomochiral halide perovskites have gained increasing attention because of their fascinating optoelectronic properties and prospective applications in laser technologies. However, the limited choice of chiral organic templates severely restricts their structural diversity and second‐harmonic generation (SHG) effects. Here, we present an in situ chiral template approach for the synthesis of one‐dimensional (1D) homochiral lead iodides. A chiral imine (L‐ipp) template was generated in situ by reacting L‐proline (L‐pro) and acetone under ambient conditions. Notably, L‐ipp can cooperate with L‐pro to direct the formation of a homochiral lead iodide with dual chiral templates, which is unprecedented in crystalline metal halides. The homochiral lead iodide containing both L‐ipp and L‐pro shows a strong SHG response of 8.0 times that of KH2PO4 (8.0×KDP). The SHG efficiency is one of the largest values reported to date for any homochiral lead halides under 1064 nm laser irradiation. A comparative study shows that homochiral 1D lead iodides containing either L‐ipp or L‐pro exhibit relatively weak SHG responses (≤1.0×KDP). This work demonstrates the advantage of using two different chiral templates over a single chiral template in enhancing the SHG responses of halide materials.