Infrared (IR) nonlinear optical (NLO) crystals play important roles in IR laser technologies and devices; however, existing materials fall short of meeting the stringent requirements of the high-power laser market. Consequently, the discovery of novel candidates remains a pressing priority. Here, a series of Zr-based thiophosphate NLO crystals A3Zr2(PS4)(P2S7)2 (A = K (1), Rb (2), Cs (3)) were successfully synthesized via the facile reactive flux assisted metal oxide-boron-chalcogen (RF-MOBQ) method. 1-3 are the first NLO compounds with the coexistence of PS4 tetrahedra and P2S7 dimers, and both act as the NLO functional motifs. 1-3 exhibit phase-matchable second-harmonic generation (SHG) responses of 0.4-0.5 × AgGaS2. Theoretical calculation results confirm that their SHG responses originate from the synergistic effect between ZrS7 polyhedra and the two PxSy units. This work enriches the structural chemistry of Zr-based thiophosphates and provides a series of promising IR NLO crystals.

This study explores a new category of excess electrons, ametalide complexes based on 15-crown-5, i.e., AM+(15-c-5)TM- (AM+ represents Li-K; TM- is Zn-Hg), to assess their nonlinear optical (NLO) features. All designed complexes exhibit electronic and thermodynamic stability as confirmed by their vertical ionization potential ranging 2.18 to 2.95 eV and interaction energies ranging -129.89 to -214.89kcal/mol. The metalide nature of complexes is validated through natural bond orbital, frontier molecular orbital, molecular electrostatic potential, and electron localization function mapping, showing negative charge, the position of HOMO, and excess electrons over TMs. The partial density of state spectra further validates the metalide nature. The UV-vis absorption spectra show that complexes are transparent in ultraviolet region. The polarizability (αo) and hyperpolarizability (βo) analysis indicates greater NLO response with highest βo of 1.08 × 106 a.u. and αo of 1022 a.u. for Li+(15-c-5)Hg- complex. Furthermore, application of an external electric field significantly enhances the NLO response. The largest enhancement is observed for Li+(15-c-5)Hg-, where β₀ increases from 1.08 × 106 to 2.56 × 106 a.u under a positive external electric field ((+ 0.1 × 10⁻2 a.u) applied along the AM to TM direction. These findings highlight the potential of metalides as a candidate for advanced NLO materials. All the density functional theory calculations were performed at ωB97X-D functional with 6-31 + G (d,p) and LANL2DZ basis set in Gaussian 16. The GaussView 6.0 and Multiwfn software were used to analyze electronic properties and view geometries of complexes.

The investigation of mechanisms for the controlled excitation and modulation of localized optical field structures remains a pivotal theme in nonlinear optics. This study synergizes similarity transformations with the Darboux transformation to derive exact analytical solutions for dispersion-decaying fiber systems. Leveraging these solutions, the dynamic evolution of multi-configurational rogue wave signals within such fibers is systematically elucidated, unveiling the intricate processes underlying nonlinear localized waveform transformations. It is demonstrated that by tailoring the topological configuration of the initial rogue wave, a diverse array of soliton pulses can be deftly excited, encompassing W-shaped solitons, double-peaked solitons, double W-shaped solitons, paired dark-anti-dark solitons, triple W-shaped solitons, and triple-peaked solitons. This novel approach, predicated upon the rogue wave evolution trajectory, transcends the conventional constraints of parameter modulation, thereby offering an innovative paradigm for optical soliton manipulation. The resultant heterogeneous soliton architectures exhibit considerable promise for optical information transmission: dark solitons, with their robust interference resistance, are ideal for high-fidelity optical communication systems; multi-peak solitons’ temporal modulation capabilities facilitate the construction of all-optical logic switches; meanwhile, composite modes of distinct soliton morphologies provide pioneering optical sources for biomedical multimodal imaging. This work not only broadens the theoretical landscape of nonlinear localized wave phenomena but also lays a foundational framework for the advancement of novel photonic devices.

The chiral ligand (R)-3-(1-carboxyethoxy)benzoic acid [(R)-H2cea], was synthesized by modifying an aromatic carboxylic acid with lactic acid. This ligand was used to react with Zn2+ and Cd2+ ions under hydrothermal conditions in the presence of N-containing heterocyclic auxiliary ligands [1,4-bis(2-methyl-1H-imidazol-1-yl)benzene (1,4-bmib) and 1,1'-(2,5-dimethyl-1,4-phenylene)bis(1H-imidazole) (2,5-dpb)], successfully constructing two chiral coordination polymers (CPs), namely, poly[[μ-1,4-bis(2-methyl-1H-imidazol-1-yl)benzene-κ2N:N'][μ-(R)-3-(1-carboxylatoethoxy)benzoato-κ2O:O']zinc(II)], [Zn(C10H8O5)(C14H14N4)]n or HCU40-R, and poly[[μ-1,4-bis(1H-imidazol-1-yl)-2,5-dimethylbenzene-κ2N:N'][μ-(R)-3-(1-carboxylatoethoxy)benzoato-κ4O,O':O'',O''']cadmium(II)], [Cd(C10H8O5)(C14H14N4)]n or HCU41-R. Both CPs crystallize in the chiral space group P21, and the central chirality from the (R)-cea2- anion is transferred and amplified into supramolecular helical chirality. In HCU40-R, the Zn2+ ions adopt a tetrahedral geometry, forming a one-dimensional right-handed helical chain that further extends into a two-dimensional helical layer. In HCU41-R, the Cd2+ ions exhibit an octahedral geometry, displaying a double-helical chain and a twofold interpenetrated two-dimensional layered structure. Powder X-ray diffraction and elemental analysis confirmed the phase purity of the samples. Thermogravimetric analysis revealed thermal stability up to 350 °C for HCU40-R and 300 °C for HCU41-R. Fluorescence measurements showed emission peaks at 451 nm for HCU40-R and 491 nm for HCU41-R. Furthermore, both compounds exhibited second-order nonlinear optical (NLO) effects, with second harmonic generation (SHG) intensities of 0.38 and 0.35 times that of KDP, respectively.

The influence of substitution position on the photophysical and charge transfer properties of isomeric carbazole derivatives.

Electrochemical switch-on of second-order non-linear optical (NLO) responses (β) has been demonstrated in a polyoxometalate (POM) based chromophore (POMophore) for the first time. Reduction of the POM in a POM-imidoaryl-NO2 derivative invokes an up to 15-fold off/on switchable increase in intensity of scattered frequency-doubled light, and the highest "on" state β yet reported for a redox-cyclable POMophore. Computational and spectroscopic studies show that in the oxidized state, directionally opposed charge transfer (CT) transitions to POM and ─NO2 result in a low net β. Upon reduction, the POM becomes a much weaker CT acceptor, resulting in more dipolar imido-aryl to nitro CT, and thus enhanced NLO response.

Chalcogenides are promising candidates to solve the scarcity of currently applicable middle nonlinear optical (NLO) crystals. Herein, heterovalent cosubstitution strategy was applied to [KBa4Cl][Ge3S10] (0), which resulted in the discovery of new ABa3EuGe3S11 (A = Na (1), K (2)). Both of them were synthesized via the reactive flux assisted metal oxide-boron-chalcogen (RFMOBQ) routine, and crystallize in the chiral P63 space group. Their quasi-3D structures are constructed by EuS7 monocapped trigonal prisms and Ge3S9 rings when considering the covalence of Eu-S bonds, which are different from the isolated Ge3S9 cluster in 0. 1 and 2 show strong NLO responses (0.7 and 0.6 × AgGaS2@2.1 μm) and enhanced laser-induced damage thresholds (4.01 and 4.85 × AgGaS2@1064 nm). This work provides a referential case for increasing the structural dimension, which can be applied to the exploration of new NLO crystals.

Birefringence, as a manifestation of optical anisotropy in crystalline materials, is a fundamental physical property that plays a crucial role in nonlinear optics, polarization control, and photonic device engineering. Traditionally, birefringence has been primarily ascribed to geometric anisotropy in crystal structures. However, recent research has demonstrated that anisotropic electronic distributions, even in geometrically symmetric frameworks, can significantly enhance optical anisotropy. In this work, we report on the synthesis, structural characterization, and optical property evaluation of Rb2ZnGe3Se8, a newly identified member of the AI2BIIMIV3Q8 chalcogenide family, which exhibits a large theoretical birefringence of 0.257 at the wavelength of 1064 nm. First-principles calculations reveal that the large birefringence arises from spatially anisotropic electron distributions within the [GeSe4] tetrahedra, rather than from overt structural distortion. The results highlight a distinct electronic origin of birefringence and expand the current understanding of how directionally polarized bonding interactions can induce significant optical anisotropy in nominally symmetric frameworks. This work deepens the understanding of structure-electronic-optical coupling mechanisms in layered chalcogenide frameworks and supports the rational design of materials with large birefringence.

Developing high-performance mid-infrared nonlinear optical (NLO) crystals is crucial for modern laser technology. Here, three novel salt-inclusion Eu-based chalcogenides (SICs) were successfully synthesized via a guest-framework modulation strategy: [KEu4Cl][Ge3S10] (1), [Eu4Cl2][Ge3S9] (2), and [Eu7Cl2][Ge6Se18] (3). They exhibit diverse structures, where the [Ge2Se6]4- dimer violates Pauling's third rule. 1-3 exhibit SHG responses of 0.3-0.9 × AGS and suitable bandgaps of 1.88-2.15 eV. Notably, 3 is the first Ge-containing SIC to demonstrate phase-matching behavior. Theoretical calculations reveal that the [Ge2Se6]4- dimer in 3 exhibits enhanced polarizability anisotropy and hyperpolarizability due to its unique connectivity mode. This work systematically demonstrates the potential of rare-earth elements in expanding the structural diversity of SICs and optimizing their NLO properties.

Zirconium/hafnium fluorides have recently garnered considerable interest as potential optical materials, owing to their short ultraviolet (UV) cutoff edges. Transforming centrosymmetric (CS) structures into noncentrosymmetric (NCS) analogues through cationic regulation has proven to be an effective approach for the development of nonlinear-optical (NLO) materials. Herein, various Zr/Hf-based fluorides with different alkali-metal cations, including K8M5F28(H2O) (M = Zr(1), Hf(2)), CsNaHfF6 (3), and LiK10M6F35(H2O)2 (M = Zr(4), Hf(5)), were synthesized. 1-3 belong to centrosymmetric space groups, whereas 4 and 5, incorporating the Li+ cation with a small radius, exhibit NCS crystal structures. 1 and 2 feature chain-like anionic structures. 3 presents a zero-dimensional (0D) anionic structure constructed from isolated [HfF6]2- octahedra. Compounds 4 and 5 adopt three-dimensional (3D) anionic networks. The introduction of Li+ enhances structural distortion and dipole alignment, resulting in phase-matchable (PM) second-harmonic-generation (SHG) responses. Notably, all compounds exhibit UV absorption edges below 200 nm, confirming superior UV transparency. Overall, these results indicate that alkali-metal regulation is an efficient approach to trigger symmetry breaking while concurrently enabling SHG activity and maintaining short UV absorption edges.

A material system with strong and broadband optical second-order nonlinearity in the near-infrared is theoretically and experimentally demonstrated. Multiple units of TiN-based coupled metallic quantum wells with slightly shifted nonlinear response peaks are uniquely designed and epitaxially grown to form a multilayered stack. By measuring near-infrared to visible second-harmonic generation, second-order susceptibility χ(2) reaches 740 pm V-1 at 900 nm and spreads 200 nm, covering the wavelength range from 800 nm to 1000 nm. Our discoveries open up the possibility to create materials with tailored optical nonlinearity, which can be valuable for building nonlinear optical devices in the fields of bioimaging, ultrafast light source generation, and quantum information technologies.

Coordination-driven self-assembly provides an effective strategy for the precise construction of supramolecular nonlinear optical (NLO) materials, yet its potential in third-order NLO applications remains insufficiently explored. Herein, we report a rhombic Pt(II) metallacycle (MPt) constructed via Pt-N coordination-driven self-assembly, achieving markedly enhanced third-order NLO responses that are confirmed to originate from the formation of the metallacyclic structure. Benefiting from the enhanced spin-orbit coupling (SOC) induced by multinuclear Pt(II) nodes and framework rigidification, MPt promotes intersystem crossing (ISC), suppresses triplet-state nonradiative decay, prolongs the triplet-state lifetime to 8.18 μs and strengthens excited-state absorption (ESA). As a result, MPt displays pronounced reverse saturable absorption (RSA) at 532 nm, outperforming the benchmark NLO material C60. Furthermore, the fabricated MPt@PDMS film exhibits excellent optical power limiting (OPL) performance, with an effective nonlinear absorption coefficient (βeff) of 1045.70 cm GW-1 and a low optical limiting threshold (FOL) of 0.23 J cm-2, placing it among the best-performing polymer-based OPL films reported to date. This work provides valuable insight into the rational design of high-performance supramolecular NLO assemblies and establishes supramolecular topological engineering as an effective strategy for amplifying third-order NLO responses.

The macroscopic nonlinear optical (NLO) response of T2 supertetrahedra strongly depends on their arrangement in the crystal lattice. Without effective symmetry control, disordered spatial orientations of these building units cause mutual cancellation of their microscopic hyperpolarizabilities, resulting in substantial reduction of the macroscopic NLO coefficients. Regulation of T2 supertetrahedron polymerization with alkali and alkaline earth metals has garnered extensive attention. Herein, we apply a strategy using zero-dimensional (0D) guest species in salt-inclusion chalcogenides (SICs) to influence coherent alignment of T2 supertetrahedra in the three-dimensional (3D) host framework. By tuning the 3D structural polymerization of the host [Cd11In9Se26]3-via the 0D guest [Rb4Cl]3+ polycation, we successfully synthesized the SIC [Rb4Cl][Cd11In9Se26]. Under the influence of the [Rb4Cl]3+ polycation, the T2 supertetrahedral units exhibit highly uniform orientational alignment. Experimental measurements and theoretical calculations reveal a bandgap of 1.70 eV, while first-principles calculations give NLO coefficients of d15 = d31 = -10.845 pm V-1, d24 = d32 = -9.957 pm V-1, and d33 = 14.757 pm V-1. This work demonstrates the 0D-guest modulation of 3D-framework alignment and provides new avenues for designing high-performance infrared (IR) NLO crystals.

Plasmons with nearly dispersionless, long-lived behavior in momentum space have great potential for novel imaging techniques and nonlinear optics, due to their ability to generate localized plasmon wave packets and to enhance giant light fields in real space. However, flat plasmons typically manifest in low-dimensional systems that conventionally originate from intraband free electrons and are usually confined to restricted momentum regions (q < ∼0.7 Å-1), which limits their applications. Here, we report the emergence and polymorphic phase-engineering of flat plasmons in the strongly correlated oxide Ti2O3, characterized by highly anisotropic and long-lived behavior (q > 0.7 Å-1). The electronic correlation effect, that is, the on-site Coulomb interaction (U), was tuned by polymorphism through epitaxial stabilization. We demonstrate a close relationship between U and the energy fluctuation of plasmons (Δωp). Specifically, a larger U leads to smaller Δωp, that is, a stronger electronic correlation effect makes plasmons flatter. This tunability can be attributed to the renormalized bandwidth of Hubbard bands, which contribute to the generation of those flat plasmons. Our work offers a practical strategy for manipulating flat plasmons in strongly correlated systems, thereby promoting the development of novel plasmonic and nonlinear optical devices.

Although noncentrosymmetry is an essential prerequisite for second-order nonlinear optical (NLO) effects, achieving it remains synthetically challenging. To date, the flux method has seldom been utilized to induce a transition from centrosymmetric to noncentrosymmetric structure. Herein, we successfully synthesized the noncentrosymmetric α-Ba2Ge4S10 phase via flux-induced symmetry breaking from centrosymmetric β-Ba2Ge4S10, enabling the growth of millimeter-sized single crystal (up to 10 × 4 × 4 mm3) using a sealed-system flux method. Structurally, the structure of α-Ba2Ge4S10 consists of zero‑dimensional supertetrahedral [Ge4S10]4- clusters charge-balanced by Ba2+ ions. Optically, α-Ba2Ge4S10 displays a competitive phase‑matching second-harmonic generation response (1.2 × AgGaS2 @2050nm) and a broad infrared transparency range (2.5-12.8µm). To our knowledge, this is the first NLO material based on T2-[Ge4S10] clusters. Moreover, the introduction of electropositive Ba2+ as a structural spacer in α-Ba2Ge4S10 contributes to a wide optical band gap (3.15eV) and a significantly enhanced laser‑induced damage threshold (14.8 × AgGaS2), underscoring its promising NLO applicability. This study demonstrates that controlled phase transformation from centrosymmetric to noncentrosymmetric structures via the flux method offers a viable strategy for designing high‑performance NLO materials.

This work investigates how the spatial arrangement of host-guest complexes influences their nonlinear optical (NLO) responses, focusing on the isomerism of cycloparaphenylene (CPP) and fullerene (C60) systems. Using density functional theory (DFT), we compare the geometry and NLO properties of C60 located inside (C60 in) and outside (C60 out) of boron- and nitrogen-doped nanorings (BCP and NCP). C60 in form is more stable due to strong dispersion interactions, while C60 out isomers yield significantly higher first hyperpolarizabilities (βtot). This performance difference arises from the distinct charge-transfer (CT) pathways, where C60 out@BCP exhibits large intramolecular CT within the host, whereas C60 out@NCP induces a new intermolecular CT process from the host to the guest. Furthermore, C60 out form exhibits high sensitivity to external electric fields, allowing for effective modulation of second-order NLO responses. These findings propose that C60 out form is distinct from the traditional C60@[10]CPP, offering new idea for designing high-efficiency organic optoelectronic materials.

Integrated photonics has enabled the miniaturization and development of classical as well as quantum-optical technologies. However, traditional lithographic techniques limit the required optical elements to binary height profiles. By relaxing these constraints, grayscale fabrication methods have the potential to deliver more efficient and compact devices. In contrast to binary profiles, wavy surfaces (also known as optical Fourier surfaces, OFSs) only introduce spatial frequencies that are required for their functionality, yielding more control over the optical response. In this work, we demonstrate photonic integrated circuits with grayscale OFS elements in state-of-the-art material platforms, including silicon-on-insulator and thin-film lithium niobate. Using thermal scanning-probe lithography and dry etching, the OFSs are written and transferred with high fidelity. We employ an intuitive and straightforward design scheme to create a series of devices that exploit the capabilities of wavy height profiles. First, we fabricate sinusoidal single- and multiband Bragg reflectors in silicon waveguides with an extinction ratio of up to 44 dB at 1550 nm. Second, cavities in lithium-niobate waveguides are fabricated with a high quality factor of 1.6 × 105 and a theoretical modal volume of 2.4(λ/n)3. Finally, we exploit this high-quality-factor cavity and the large optical nonlinearity of lithium niobate to produce frequency-doubled light via second harmonic generation.

Plasmons in atomically thin materials offer a compelling route to trigger nonlinear light-matter interactions through extreme optical confinement in the two-dimensional (2D) limit. However, optical nonlocality in plasmons is typically associated with losses in the linear response regime. Here, we show that nonlocal effects mediate strong plasmon-assisted optical nonlinearity in electrically reconfigurable 2D heterostructures. Using atomistic simulations that capture quantum finite-size and nonlocal effects in the nonlinear plasmonic response of graphene and phosphorene nanoribbon dimers, we reveal how symmetry and inter-ribbon coupling shape harmonic generation processes in perturbative and high-harmonic regimes. Independent tuning of geometry and carrier density in nanoribbon heterostructures is shown to induce inter-ribbon plasmon hybridization, impacting inversion symmetry governing even-ordered nonlinear processes like second-harmonic generation. These results reveal design principles for the active and passive tuning of nonlinear plasmonic effects and enable selective enhancement of specific harmonic processes, establishing 2D heterostructures as a versatile platform for nonlinear nanophotonics.

This paper reports the study on the synthesis, characterization, linear and nonlinear optical (NLO) properties of the Schiff base N',2-bis((E)-4-hydroxy-3-methoxybenzylidene)hydrazine-1-carbohydrazide (HPMC). The Schiff base was characterized by UV-Visible absorption, FT-IR, 1H and 13C NMR, confocal Raman and Mass spectroscopy techniques. The chemical compounds of the Schiff base were identified by FT-IR and Raman Spectroscopy. The molecular weight of the compound was confirmed by Mass spectroscopy. The chemical shift with total number of protons and carbons of the Schiff base HPMC was calculated using 1H and 13C NMR spectroscopy. Z-scan technique was used to measure the third-order NLO features of the sample, which revealed a significant third-order NLO susceptibility of 7.19 × 10- 7 esu. The nonlinear refractive index and absorption coefficient of HPMC was ascribed to saturable absorption (SA) and self-defocusing. Furthermore, the experimental results were validated by theoretically using density functional theory (DFT) B3LYP functional with the 6-311G(d, p) basis set. The molecular polarizability, electrostatic potential, frontier molecular orbit of the Schiff base was validated theoretically. The experimental and theoretical results divulged that the Schiff base N',2-bis((E)-4-hydroxybenzylidene)hydrazine-1-carbohydrazide was a potential NLO material for photonics and optoelectronics applications.

Atomic clusters are promising candidates for nonlinear optical (NLO) materials owing to their diverse geometric configurations and tunable electronic structures. With the development of preparation techniques, various atomic clusters, particularly carbon clusters, have been experimentally synthesized. However, understanding how cluster geometries relate to NLO response remains limited, largely because their geometric and electronic complexity prevents direct transfer of insights from traditional molecular systems. In this work, the linear and third-order NLO responses were investigated using carbon clusters as model systems, revealing that geometric evolution─from cage and planar-porous to cyclic to linear structures─continuously enhances both responses, driven by increased electron delocalization along less confined directions. Consequently, linear structures represent the optimal geometry to maximize these responses in carbon clusters. Additionally, unlike the strong dependence between optical response and the HOMO-LUMO gap that exists in traditional organic systems, predicting the linear and third-order NLO responses in carbon clusters via the HOMO-LUMO gap is infeasible owing to the absence of crucial excited states in generic geometric systems. These insights are further confirmed in multielement boron nitride cluster systems. This study provides deep insights into the linear and third-order NLO behaviors of atomic clusters and a clear design guideline for developing these materials.