Themed collection FOCUS: Nonlinear Optical Materials

This work reviews selenoborates, categorizing them by structure, synthesis methods, and highlighting their bandgaps, nonlinear optical properties, and potential as IR functional materials.

The calculated polarizability anisotropy, hyperpolarizability and HOMO–LUMO gap of optically active groups.

This review article provides an overview of Mg-based IR nonlinear optical materials including synthetic methods, structural chemistry, structure–activity relationships, current problems and future development.

Two new borate–sulfates form unique three-dimensional (3D) porous frameworks with embedded [SO₄] units. The transition from structure I to II is driven by differences in cationic radii, leading to distinct 3D porous borate anionic frameworks.

Hg₂(HTe₂O₅)(PO₄) exhibits a large birefringence of 0.162 at 546 nm and a wide band gap of 3.58 eV, achieved through the synergistic modification of multiple functional groups.

Efficient optical power limiting (OPL) materials are crucial for protecting optical devices and the eyes.

Bulk crystal growth of a novel organic–inorganic hybrid nonlinear optical thiocyanate: [Mn(CH₃CONH₂)₂] [Hg(SCN)₄], exhibiting a significant second-harmonic generation response approximately 2.5 times greater than that of KDP.

Thermally driven CS-to-NCS transition: an irreversible phase transition pathway for high-performance infrared nonlinear optical crystal Ag₄P₂S₇.

By incorporating multiple alkali and alkaline-earth metal elements, we have successfully synthesized and report the first tri-alkali/alkaline-earth metal fluorophosphate KBaSr(PO₂F₂)(PO₃F)₂ as a promising deep-ultraviolet birefringent crystal.

CdF(C₆H₄NO₂)(H₂O) emerges as a UV nonliner optical material that exhibits unprecedented second harmonicgeneration (3.2×KDP) and birefringence (0.26@546 nm), achieved through the presence of π-conjudated rings and a distinctive “Warren truss structure”.

By modifying the KBBF template structure at the molecular level, the first metal-free sulfate (CN₄H₇)₂SO₄·H₂O was synthesized, which achieved an effective balance between the short UV cut-off edge (212 nm) and large birefringence (0.132@546.1 nm).

DUV NLO crystals LiBePO₄ and BeP₂O₆ adopting a Cs₄LiBe₄P₇O₂₄ structural model were synthesized using an ionic potential modulation strategy. The arrangement of PO₄ groups exhibits uniform evolution, inducing increased SHG effects.

A novel NLO material, SbOCl·DMSO, has been successfully designed, demonstrating a large SHG coefficient of 4.4 × KDP, moderate birefringence of 0.084@546 nm and a short UV cut-off edge of 331 nm.

Ultraviolet (UV) nonlinear optical (NLO) crystals with a second-harmonic generation (SHG) response can efficiently output UV coherent light, and have important applications in UV solid-state lasers.

A novel Eu-based chalcogenide, β-EuZnGeS₄, has been designed using an isovalent cation substitution strategy, starting from the centrosymmetric Eu₂GeS₄, and it demonstrates well-balanced IR NLO performance.

Combined machine-learning with experimental evaluations, the thermal conductivities in IR nonlinear optical chalcogenides Li_xAg_1−xGa_yIn_1−ySe₂ series are investigated, and three compositions exhibit balanced properties.

Four DUV sulfamate halide co-crystals, AX(NH₃SO₃) (A = Rb, Cs; X = Cl, Br), have been successfully synthesized by combining [XA_m] secondary building units with [NH₃SO₃] polar tetrahedra, leading to a significant enhancement in birefringence.

Ca₂La(Ge_0.72Si_0.28S₄)(BS₃) and Ca₂La(Sn_0.75Si_0.25S₄)(BS₃) are designed by mixing Ge⁴⁺ or Sn⁴⁺ into the Si⁴⁺ site and they achieve obviously enhanced SHG effects.

We modified the perovskite ABX₃ structure by substituting X-site with NH₂SO₃⁻, using Cd²⁺ at B-site and K⁺ at A-site. This resulted in DUV transparency (<190 nm), strong SHG (>1.1 × KDP), and easy growth (20 × 17 × 5 mm³).

Tin chalcohalide Sn₁₁(PS₄)₄I₁₀ is a balanced-performance IR NLO material obtained by structural-template-oriented synthesis.

The flexibility index, previously proposed to clarify the structural origin of second-order nonlinear optical responses, is demonstrated to be a general descriptor to characterize polarizability-relevant properties.

Two novel antimony halide crystals RbSbF₃Cl and Rb₃Sb₄F₁₄Cl were synthesized. Rb₃Sb₄F₁₄Cl exhibits a strong SHG response of 3 × KDP and a broad transparency range of 0.27–13.3 μm, while RbSbF₃Cl features a large birefringence of 0.31 at 546 nm.

A rare earth borate UV NLO crystal, K_7.5Lu_2.5B₁₅O₃₀, was obtained through a chemical substitution strategy. This crystal exhibits a strong SHG response and a short UV cut-off edge.

This work demonstrates that aliovalent cation substitution is an effective strategy for discovering new thioantimonate(V) families and suggests that cation size effects from substitution can lead to performance improvements.

This study achieved structural modulation from 0D aluminum rings to 2D MOF via a coordination-driven self-assembly strategy. Notably, the exfoliated nanosheets showed enhanced NLO properties, highlighting their potential in optical applications.

A noncentrosymmetric phosphate (C₃H₅N₂)(H₂PO₄) with pseudo 2D intercalated layers, which exhibits large birefringence and wide band gap, was successfully synthesized by simultaneously introducing the planar and tetrahedral motifs.

Waterproof 0D hybrid Zn halide with highly efficient blue emission and third-order nonlinear optical response was constructed by the microregulating of π–π interactions, offering new insights for designing stable multifunctional halide materials.

(C₃N₆H₇)BF₄·H₂O and (C₃N₆H₇)SO₃CH₃·H₂O with large birefringence.

Crystal structures and optoelectronic performance of hybrid two-dimensional lead bromide halide perovskites are elaborately regulated by pyridyl cations, which achieve a significantly enhanced birefringence of 0.315 (550 nm) for crystal 2.

High-throughput screening of 222 hydroxyborates identified three as promising short-wavelength ultraviolet nonlinear optical. with phase-matching second harmonic generation capacity extending to the solar blind region (200–280 nm).

The acentric Ce(IV) fluoride NH₄Ce₃F₁₃ is systematically studied, exhibiting the strong SHG effect (1.2 × KDP) and high LIDTs (39 × AGS). It also possesses the largest band gap among NLO materials containing Ce(IV).

An acentric lead titanium-tellurate crystal, Pb₄Ti₃TeO₁₃, was extracted using spontaneous crystallization with the pyrochlore structure as a template. It exhibited a large SHG response and a wide transmission range.

γ-Bi₂MoO₆ exhibits a 9.9-times stronger second harmonic generation (SHG) response than that of KDP, large birefringence of 0.21 at 1064 nm, and relatively large band gap of 2.57 eV.

Two new hybrid metal halides (C₁₃N₃H₁₄)₂MBr₄ (M = Zn, Cd) were obtained by three-in-one-strategy, exhibiting comprehensive high-performance NLO properties. Besides, the composition-structure-NLO properties relationship is well studied.

We have rationally synthesized a chiral sodium lanthanum sulfate, NaLa(SO₄)₂(H₂O), through the complementary integration of alkali and rare-earth cations. The compound exhibits a high proton conductivity and SHG response with a high birefringence.

By introducing [AgS₃] and [NaQ₆] (Q = S, Se) into the A^IRE^IIIC^IVQ^VI₄ family, four new RE-based chalcogenides with wide band gaps and large birefringence have been rationally designed and fabricated.

Two new fluoroaluminoborates, BaAlB₃O₆F₂ and BaAl₂(B₃O₆)₂F₂, were designed and synthesized, exhibiting a markedly elevated birefringence in comparison with BaAlBO₃F₂.

Multi-step cation substitution is an effective method to regulate the tetrahedral frameworks and enhance infrared nonlinear optical performance.

Presented herein is a designed synthesis toward the enhancement of intended optical properties through a supracluster assembly strategy based on a pre-designed Al₄ precursor.

The halide substitutions in (C₄H₁₁N₂)ZnX₃ (X = Cl, Br, I) induce polarity tuning and then optimized SHG-bandgap balance.

M_xEu_18−xGe₉O₅S₃₁ (R3) were obtained by cationic and anionic co-partial substitution of β-Eu₂GeS₄ (P2₁/m), which induced centrosymmetric to noncentrosymmetric structural transformation and balanced second-order nonlinear optical activity.

The novel tin(II) phosphate compound [Sn₃OF]PO₄ exhibits significantly greater birefringence compared with [Sn₃F₃]PO₄ (Δn_obv. = 0.117 versus 0.027@546 nm), achieved by breaking the undesirable symmetry and reorienting stereochemically active lone pairs.

Tetrahedral groups comprising [VO_xS_4−x] (x = 0–4) units have the potential to enhance birefringence characteristics. Their balanced mid-IR NLO attributes make them a promising avenue of investigation for the exploration of NLO materials.

With the aid of an open framework, multifunctional materials with NLO and magnetism were synthesized.

From (C₆H₇N₂O)⁺(H₂PO₄)⁻ to (C₆H₆NO₂)⁺(H₂PO₄)⁻: different preparation methods resulting in tuning the inorganic framework and outstanding birefringence in organic phosphates.

By combining the π-conjugated [NO₃] unit with the non-π-conjugated [SO₃NH₃] unit, a promising ultraviolet nonlinear optical (NLO) crystal RbNO₃SO₃NH₃ with excellent comprehensive performance was successfully obtained.

A novel excellent IR-NLO material RbPbPS₄ with superior comprehensive performances is provided, representing the first quaternary Pb-based chalcogenide breaks through the incompatibility between a large E_g and a strong d_eff.

Presented herein is a “two birds with one stone” strategy of designing an unprecedented deep-cavity aluminum organic macrocycle to trap dye waste and generate efficient optical limiting properties.

The second harmonic generation effect and birefringence of (C₁₀H₁₁N₃)BX₄ perovskites are considerably enhanced via structural evolution and halogen substitution strategies.

Enhancing the birefringence of compounds by “two steps in one”: a synergistic strategy of stereochemically active lone pairs [SeO₃] and distorted [VO₆] polyhedra.

Using the SbOCl compound as a template, we researched six antimony(III) oxyhalides via single-site substitution, which are favorable for generating birefringences greater than 0.1.

Four pairs of enantiomers of ferromagnetically coupled Dy₂ single-molecule magnets, which show both strong magneto-optical Faraday effects and strong third-harmonic generation, are directionally constructed.

In the three structures, the substitution of large-size cations results in the rearrangement of the anionic group, and their birefringence exhibits a progressive doubling increase, transitioning from 0.017, 0.033 to 0.070 at 532 nm.

The long-neglected stereochemically active lone pair groups ClO₃⁻ and BrO₃⁻ are demonstrated to be important UV NLO functional motifs based on the fact that AClO₃ and ABrO₃ possess high SHG effects and short λ_PM and are promising UV NLO materials.

Pb_3.5GeS₄Br₃ is the first phase-matching thiogermanate halide infrared nonlinear optical material.

A novel vanadate NLO crystal Cd₂BiVO₆ was synthesized through spontaneous crystallization, exhibiting a large SHG response, an enhanced birefringence and a wide transmittance range.

Hg-based chalcogenides, Hg₃AsS₄Cl and Hg₃AsS₄Br, are synthesized, which show superior comprehensive linear and nonlinear optical properties for promising IR applications.

Two novel 2D oxychalcogenides, AEGe₂O₄Se (AE = Sr and Ba), were designed using a partial substitution strategy which exhibits the coexistence of a wide band gap (E_g > 3.1 eV) and a large birefringence (Δn > 0.2).

(NH₄)₃[Sn₂(PO₄)₂]Cl: the rational design of a tin-based phosphate with the coexistence of large optical anisotropy and short-wave ultraviolet transparency.

A dicyanidoiridate(III) complex, bearing chiral (R,R)-2-phenyl-4,5-pinenopyridine ligands, serves as a SHG-active luminescent thermometer, optimized by embedding into a heterometallic coordination polymer.

Here, the polar covalent group (PO₃NH₃)⁻ is identified as a novel deep-ultraviolet (DUV) NLO-active unit. Its ordered arrangement in NaPO₃NH₃ makes this compound exhibiting the largest birefringence among DUV non-π-conjugated phosphate systems.

H/F substitution has been successfully applied to achieve structural dimension tailoring at the molecular level coupled with tunable dielectric and optical properties in organic lead-bromide hybrids.

Presented herein is a study focusing on the effect of organic shell ligands on the configuration of the ring structure with the same nuclearity, and their photo-related applications, such as fluorescence and third-order nonlinear response.

Combining non-π-conjugated heteroanionic groups and π-conjugated groups is an effective strategy for obtaining crystals with excellent optical properties.

NCS Pb₃(TeO₃)Br₄ was obtained based on the CS CdPb₈(SeO₃)₄Br₁₀ by mild hydrothermal reactions. Pb₃(TeO₃)Br₄ can exhibit an SHG response equivalent to KDP, appropriate birefringence, wide optical transparency window and high thermal stability.

Two novel Cs₃REGe₃O₉ (RE = Y, Gd) crystals were extracted and exhibit a breakthrough of UV cutoff edge at 210 and 215 nm, respectively, the shortest value among boron-free germanate-based NLO materials.

A novel NLO tellurate crystal, LiVTeO₅, was extracted via spontaneous crystallization. It features the attractive merits of a strong SHG response, a large band gap, a wide transmittance range, and a notable birefringence.

Non-centrosymmetric semiconductors may exhibit non-linear optical (NLO) properties.

Based on the “electronic structure engineering bucket effect”, a new AEM-containing sulfide BaZnGeS₄ with a wide band gap (∼3.36 eV) and large SHG response (∼0.8× AGS) has been designed and synthesized via high-temperature solid-state reactions.

Two novel 1D quinary oxychalcogenides, Ba₃M^IIGe₃O₂S₈ (M^II = Mn, Cd), were designed using a heteroanion-introduction strategy, which exhibit a significant enhancement in birefringence compared to the known 3D framework AE₃M^IIM^IV₂Q₈.