Large Optical Nonlinearity Research Articles

Shooting mid-infrared nonlinear optical materials with targeted balance performances in ternary d0-transition metal oxides through first-principles

Heavy metal oxides are emergent candidates for mid-infrared nonlinear optical (NLO) materials, which might achieve a targeted balance property between the idea band gaps and large NLO coefficients. However, the ternary d0-transition metal oxides as mid-infrared NLO materials have not been systematically investigated by the first-principles. Herein, taking ternary d0-transition metal oxides as a research subject, we collected 94 non-centrosymmetric compounds in the inorganic crystal structure database for screening excellent mid-infrared NLO crystals. Among them, seven compounds are highlighted: HT-La2Ti2O7, ZrMo2O8, Rb3V5O14, β-Tl3VO4, La2MoO6, WO2Cl2, and WOCl4. They have a good balance between the wide band gaps 3.01–4.33 eV and large NLO coefficients of 0.5–0.7 × AgGaS2 (d36 = 13.4 p.m./V), simultaneously possess moderate birefringence of 0.055–0.438 at 1064 nm. This study will provide a guideline for exploring new mid-infrared NLO materials with targeted balance performances in ternary d0-transition metal oxides.

ASecond-Order Nonlinear Optical Material Consisting of Two π-Conjugated Groups.

Herewereporta second-order nonlinear optical (NLO) material [C(NH2)3]3C3N3S3(GU3TMT), consisting ofπ-conjugated planar (C3N3S3)3-and triangular [C(NH2)3]+groups. Interestingly, GU3TMT exhibits large NLO response (2.0x KH2PO4) and moderate birefringence 0.067 at550 nm, even though (C3N3S3)3-and [C(NH2)3]＋do not exhibit the most favorable arrangement in the structure of GU3TMT. First-principles calculations suggest that NLO properties mainly originate from the highlyπ-conjugated (C3N3S3)3-rings, and theπ-conjugated [C(NH2)3]＋triangles contribute much less to the overall NLO response. This work will inspire new thoughts with in-depth on the role ofπ-conjugated groups in NLO crystals.

Partial substitution induced structural transformation and enhanced nonlinear optical properties of Na2GaxIn6-xSe10 (x = 3, 3.76)

Chalcogenides are the most promising candidates for nonlinear optical (NLO) applications in the middle infrared region due to their high nonlinear coefficients and wide IR transmission ranges. In particular, polar tetrahedral units are one type of typical functional motifs contribute large NLO coefficients. Based on this background, two quaternary selenides Na2Ga3In3Se10 (1) and Na2Ga3.76In2.24Se10 (2) were derived using NaIn3Se5 as parent. By partial congener substitution of In with Ga, the structure transforms from P32 for NaIn3Se5 to R32 for 1 and 2. Their 3D structures are constructed by InSe4 and GaSe4 tetrahedra, and Na+ ions occupy the octahedral cavities. Both of them exhibit wonderful hybrid NLO properties, witnessed by their large phase-matchable second harmonic generation responses of 1.5 (1) and 1.1 (2) × AgGaS2 (AGS), and enhanced laser-induced damage thresholds of 2.0 (1) and 2.8 (2) × AGS. The results of first-principle calculations show that their band gaps are mainly determined by the valence orbitals of Ga and Se, with a minor contribution from In. The simple design strategy adopted in this work can stimulate more research on various known materials, which will provide useful inspiration for further exploration of high-performance NLO materials. Besides, the successful discovery of 1 and 2 will stimulate more interest in the undeveloped A-MШ3-Q5 or A2-MШ6-Q10 (A = alkali metal; MШ = Ga, In; Q = S, Se, Te) family and their derivatives in the NLO field.

Graphene Oxide for Nonlinear Integrated Photonics

AbstractIntegrated photonic devices operating via optical nonlinearities offer a powerful solution for all‐optical information processing, yielding processing speeds that are well beyond that of electronic processing as well as providing the added benefits of compact footprint, high stability, high scalability, and small power consumption. The increasing demand for high‐performance nonlinear integrated photonic devices has facilitated the hybrid integration of novel materials to address the limitations of existing integrated photonic platforms. Recently, graphene oxide (GO), with its large optical nonlinearity, high flexibility in altering its properties, and facile fabrication processes, has attracted significant attention, enabling many hybrid nonlinear integrated photonic devices with improved performance and novel capabilities. This paper reviews the applications of GO to nonlinear integrated photonics. First, an overview of GO's optical properties and the fabrication technologies needed for its on‐chip integration is provided. Next, the state‐of‐the‐art GO nonlinear integrated photonic devices are reviewed, followed by comparisons of the nonlinear optical performance of different integrated platforms incorporating GO as well as hybrid integrated devices including different kinds of 2D materials. Finally, the current challenges and future opportunities in this field are discussed.

Modulation of epsilon-near-zero wavelength and enhancement of third-order optical nonlinearity in ITO/Au multilayer films

We report the modulation of epsilon-near-zero (ENZ) wavelength and enhanced third-order nonlinearity in indium tin oxide (ITO)/Au multilayer films. The samples consisting of five-layer 40 nm ITO films spaced by four-layer ultrathin Au films of different thickness, i.e., ITO(40 nm)/[Au(x)/ITO(40 nm)]4, were prepared by magnetron sputtering at room temperature. The ENZ wavelength in the multilayer films is theoretically calculated and experimentally confirmed. The nonlinear refractive index and nonlinear absorption coefficient of the samples of x=0, 2, 3, 4 nm were determined using the Z-scan method at a wavelength of 1.064 µm. The large nonlinear refractive index n2=1.12×10-13 m2/W and nonlinear absorption coefficient β=-1.78×10-7 m/W in the sample of x = 4 nm are both four times larger than those in the single-layer ITO film. The large optical nonlinearity due to the ENZ enhancement and carrier concentration is discussed. The results indicate that the ITO/Au multilayer films are promising for advanced all-optical devices.

Broadband THz wave generation in organic benzothiazolium crystals at MHz repetition rates [Invited

We present broadband terahertz wave generation based on benzothiazolium crystals at a 100 MHz repetition rate. Among various benzothiazolium crystals, we chose PMB-4TFS (2-(4-(4-(hydroxymethyl)piperidin-1-yl)styryl)-3-methylbenzothiazol-3-ium 4-(trifluorome-thyl)benzenesulfonate) due to its large macroscopic optical nonlinearity, good crystal characteristics, and suppressed molecular phonon vibrations. When pumped at the telecommunication wavelength of 1560 nm, the generated THz spectrum covers up to ∼15 THz and the corresponding THz amplitude for a 0.29 mm thick crystal at normal incidence is by more than one order of magnitude higher compared to the inorganic standard, 1.0 mm thick ZnTe generator crystal.

Thermodynamic and nonlinear optical analysis of solid-state multipass cells for compression of picosecond pulses in the 2−μm range

Multipass cells (MPCs) recently emerged as a new femtosecond pulse compression technique for lasers with high pulse energy. While most of the work focused on the compression of near-infrared laser systems so far, we address the case of holmium-based gain materials, which offer an enormous potential in terms of pulse energy, yet can only host a very narrow bandwidth in the 2-$\ensuremath{\mu}\text{m}$ wavelength range. Compression into the few-cycle regime, therefore, requires at least a hundredfold spectral broadening. Specifically, we investigate the utility of four different solid-state materials in the MPC, namely, fused silica, sapphire, YAG, and diamond. Spectral broadening dynamics is numerically investigated using the $2D+1$-unidirectional pulse propagation equation. To this end, we put particular emphasis on the thermal properties of the nonlinear optical material, which turn out as a critical issue above 2-$\ensuremath{\mu}\text{m}$ wavelength. Solving the heat equation for each of the materials, we then estimate the maximum temperature at beam center. These considerations show that outside the near infrared, thermodynamic parameters of nonlinear optical materials become at least equally important as their optical properties. Among the four materials under test, in particular, diamond stands out as it combines highly favorable thermal properties with a large optical nonlinearity. Finally, a concomitant slow degradation of spatial coherence is monitored. Our findings provide an effective guideline for the design of high pulse-energy compressors at wavelengths of $2\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\text{m}$ and beyond.

Predicting Diamond-like Nitrides as Infrared Nonlinear Optical Materials with High Thermal Conductivity

Exploration of new infrared nonlinear optical (NLO) materials is urgently needed owing to the lack of high-performance crystals to break through strict conditions of wide band gaps, large NLO coefficients, and a high laser-induced damage threshold. Herein, the high-throughput prediction strategy has been implemented, and a series of predicted nitrides in the AII–M–N systems (AII = Mg, Ca, Sr, Ba, Zn; M = Si, Ge) with the stoichiometric ratios 1:6:8, 1:7:10, 2:5:8, 5:2:6, and 1:1:2 are discovered. Among them, six diamond-like nitrides with the stoichiometric ratio of 1:1:2 are highlighted, namely, Pna21-AIISiN2 (AII = Ca, Sr) (Z = 4), Pna21-AIIGeN2 (AII = Sr, Ba) (Z = 4), and I42d-AIIGeN2 (AII = Mg, Ca) (Z = 4). The six diamond-like nitrides realize a balance between large NLO coefficients 0.5–2.0 × AgGaS2 (d36 = 13.4 pm/V) and wide band gaps of 3.30–4.72 eV due to the strong covalent interaction in M–N (M = Si, Ge) bonds. Simultaneously, the six diamond-like nitrides exhibit high Debye temperatures (634.4–913.1 K), which are beneficial to improving their thermal conductivities. Typically, the thermal conductivities at 300 K are 2.9 W/(m·K) for Pna21-BaGeN2, 4.4 W/(m·K) for Pna21-SrSiN2, and 11.7 W/(m·K) for I42d-CaGeN2, which are larger than that of the infrared benchmark AgGaS2 (1.4 W/(m·K)). This study will provide an insight into explore new infrared NLO materials with high thermal conductivity in diamond-like nitrides.

A New Class of Organic Crystals with Extremely Large Hyperpolarizability: Efficient THz Wave Generation with Wide Flat‐Spectral‐Band

AbstractIn organic π‐conjugated crystals, enhancing molecular optical nonlinearity of chromophores (e.g., first hyperpolarizability β ≥ 300 × 10−30 esu) in most cases unfortunately results in zero macroscopic optical nonlinearity, which is a bottleneck in organic nonlinear optics. In this study, a new class of nonlinear optical organic crystals introducing a chromophore possessing an extremely large first hyperpolarizability is reported. With newly designed 4‐(4‐(4‐(hydroxymethyl)piperidin‐1‐yl)styryl)‐1‐(pyrimidin‐2‐yl)pyridin‐1‐ium (PMPR) chromophore, incorporating a head‐to‐tail cation‐anion OH⋯O hydrogen‐bonding synthon and an optimal selection of molecular anion into crystals results in extremely large macroscopic optical nonlinearity with effective first hyperpolarizability of 335 × 10−30 esu. This is in sharp contrast to zero value for previously reported analogous crystals. An ultrathin PMPR crystal with a thickness of ≈10 µm exhibits excellent terahertz (THz) wave generation performance. Both i) broadband THz wave generation with a wide flat‐spectral‐band in the range of 0.7–3.4 THz defined at −3 dB and high upper cut‐off generation frequency of > 7 THz as well as ii) high‐generation efficiency (5 times higher THz amplitude than ZnTe crystal with a mm‐scale thickness) are simultaneously achieved. Therefore, new PMPR crystals are highly promising materials for diverse applications in nonlinear optics and THz photonics.

Chalcohalides: A Rising Type of Second‐Order Nonlinear Optical Materials

AbstractIn the past few decades, many new infrared (IR) second‐order nonlinear optical (NLO) materials have been prepared by various synthetic methods to satisfy the growing market demand. However, few ones have the high potentials to be applicable since their comprehensive NLO properties cannot meet the standards, which include a series of indicators like large NLO effects, high laser‐induced damage thresholds (LIDTs), phase matchability, high thermal stability, good growth habit, and so on. Considering the available IR NLO materials’ disadvantages and the market requirements, it is necessary to continuously explore new high‐performance ones. Hitherto, lots of chalcogenides, halides, and oxides have been explored as IR NLO materials. Recently, researchers have found that the combination of two or more structural units into one structure may achieve good NLO properties, as evidenced by the fact that diverse materials with multiple anions are receiving growing interest. Specifically, chalcohalides are highly promising as they may combine the advantages of chalcogenides and halides,viz. large NLO coefficients and wide IR transparency of the former, and large band gaps and high LIDTs of the latter. To address the status of chalcohalides, this review focuses on the newest progresses on this topic (mainly from the last five years), including ternary chalcohalides, quaternary chalcohalides, salt‐inclusion chalcohalides, and rare‐earth chalcohalides. Here we summarize and analyze their compositions, crystal structures, NLO properties, and discuss the structure‐property relationship. Finally, the development prospects for NLO chalcohalides are given.

Novel structural transformation in K3ReP2S8 thiophosphates originating from the rare-earth (Re) cation sizes induced local coordination asymmetry

Noncentrosymmetric (NCS) structure is a prerequisite condition for nonlinear optical (NLO) crystals and searching for feasible design strategy on the discovery of new NCS compounds has become extremely important. For that reason, new series of rare-earth (Re) based NCS K3ReP2S8 (Re = Y, Ho, Er; P21 space group) and CS K3ReP2S8 (Re = Pr, Sm, Gd; P21/c) thiophosphates were successfully prepared and this interesting CS to NCS structural remodeling shows the interior relationship with cation-size effect of Re metals. Systematic structural analysis indicates that several of varying influence factors including Re's ionic radii, average Re–S bond lengths and distortion degrees of ReS8 units induce the born of local coordination asymmetry between ReS8 and PS4 units, which facilitates the transformation from CS to NCS structures in K3ReP2S8 system. Moreover, excellent performances including strong NLO responses (1.1–1.4 times that of commercial AgGaS2) and required phase-matching behavior in P21–K3ReP2S8 were determined. Note that P21–K3ReP2S8 can be viewed as first NLO examples in the quaternary rare-earth thiophosphates. Moreover, NCS K3ReP2S8 also satisfy the well-balance between large NLO effects (1.1–1.4 × AgGaS2) and high laser damage thresholds (2.5–7.0 × AgGaS2). Theoretical study demonstrates that synergetic contributions of ReS8 and PS4 units guarantee the intrinsic origin of NLO response and ReS8 units provide the major NLO contribution. Therefore, this work not only affords one effective pathway to design new NCS materials through breaking the local symmetry in CS structures based on the size-directing effect of Re cations, but also verifies that bridging ReSn units into thiophosphates is beneficial to the huge enhancement of intrinsic NLO performances.

First Hyperpolarizabilities of Intramolecular Charge-Transfer Architectures Based on Acenaphthene Derivatives in Gas, Solution, and Solid States.

Constructing charge transfer (CT) systems and packing arrangement are common and effective methods to control the efficiency of nonlinear optical (NLO) materials. Apart from the traditional through-bond CT (TBCT) systems, through-space CT (TSCT) also leads to distinctive optical and electronic properties. Meanwhile, corresponding theoretical investigations of the aggregation effect are highly desired. In this work, some TSCT and model compounds incorporating acenaphthene as a scaffold and triphenylamine (TPA) as the donor are theoretically performed to systematically reveal the effect of both solvent and solid environments on their static first hyperpolarizabilities (βtot) by using the polarizable continuum model (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method. Results indicate that the dichloromethane solvent effect within the PCM approach causes an almost 2 times increase of the βtot values. Besides, the different packing modes and intermolecular interactions have remarkable influence on the second-order NLO properties. For the case of TPA-ace-CN in the crystal state, the parallel arrangement will lead to large NLO responses (4.9 × 10-30 esu) compared to the correspondingly isolated molecule (3.4 × 10-30 esu). However, for the TPA-ace-TRZ compound with the TSCT architecture, selection of the molecular arrangement may make the aggregate ineffective due to the offset of the through-space dipole and charge transfer between D-A groups, which lead to the βtot values decreasing from 15.2 × 10-30 to 7.7 × 10-30 esu. We believe that our calculation will serve as a guide for the exploration of more efficient NLO materials wherein the molecules are oriented in their most favorable arrangements.

Organic Chromophores from D–π–A to D–A’–π–A: Influence of the Auxiliary Acceptor on Energy Levels, Molecular Absorption, and Nonlinear Optical Response

In this research article, four organic chromophores of type D–Ai–π–A (i=2–4) combining various auxiliary acceptors (Ai) with phenothiazine (PTZ) as the electron donor, thiophene as the π-conjugated bridge, and tricyanovinyl dihydrofuran (TCF) as the electron acceptor have been structured and theoretically studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The effects of various auxiliary acceptors in D–Ai–π–A chromophores on the nonlinear optical (NLO) response have been examined. In this context, the geometric and electronic structures, intramolecular charge transfer (ICT), NBO analysis, absorption wavelength in different organic solvents, polarizability (α), and hyperpolarizability (β) have been determined. They have been assessed to predict the appropriate candidates for NLO material. The data obtained illustrate that all chromophores with various auxiliary acceptors present a large NLO response ranging from 13541.17 to 66723.38 (a.u), PTZ-2 especially with auxiliary acceptor 2,3-dimethylthieno[3,4-b]pyrazine presents the highest <a> [(879.10 (a.u)) and βtot (66723.38 (a.u)] values. A strong NLO response indicates that this series of organic chromophores with a D-Ai-π-A architecture exhibits large first hyperpolarizability βtot values, which are much greater than those of urea.

Design of novel deep-UV nonlinear optical materials with one-dimensional functional module [BO2]∞ chain and fluorine-driven short phase-matching

Design of deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials is urgently needed owing to the lack of high-performance crystals to meet the contradictory criteria of deep-UV transparency, strong NLO response and moderate birefringence to reach deep-UV phase-matching. In this work, a “highly-polymerized units optimizing electron delocalization” strategy was proposed to explore novel types of deep-UV NLO anionic functional module and design new materials. Two novel NLO systems with new NLO anionic functional module-one dimensional [BO2]∞ chains were successfully designed. In total, four LiBO2 (I-IV) and five Li2BO2F (I–V) structures with good thermodynamically and dynamically stable/metastable were obtained by using evolutionary algorithm crystal structure prediction techniques. All these structures contain the [BO2]∞ infinite chains and have deep-UV transparency (< 177.3 nm). LiBO2 (II, IV) and Li2BO2F (I, IV-V) exhibit large NLO response (2.0–2.3 × KH2PO4) and large birefringence (0.093–0.146 @1064 nm). Remarkably, Li2BO2F–I possesses an extremely short phase-matching wavelength about 159 nm, which is beneficial from the introduction of fluorine to maintain the superior functional module [BO2]∞ and optimize the optical properties. The results indicate that [BO2]∞ can be as a new deep-UV NLO functional module, this work provides an insight into the design of new deep-UV compound with outstanding NLO performances.

三元AGa5S8 (A = K, Rb, Cs): 通过“一替多取代”策略制备的红外非线性光学材料

Commercially available infrared (IR) nonlinear optical (NLO) materials, such as diamond-like AgGaQ2 (Q = S, Se), display large NLO coefficients but relatively low laser-induced damage thresholds (LIDTs), which seriously hinder their widespread laser applications. Herein, the “one-for-multiple substitution” strategy, namely, [SZn46+ + 5Zn2+ ⇒ A+ + 5Ga3+] (A = K, Rb and Cs), is applied on the diamond-like zinc-blende ZnS, and affords three new polar ternary crystals AGa5S8 (A = K, Rb and Cs) through the solid-state method. These compounds inherit the diamond-like anionic backbone framework in ZnS where the NLO functional motifs GaS4 are arranged in a parallel manner. This characteristic accounts for the remarkable phase-matchable second-harmonic generation intensities (1.1–1.2 × AgGaS2). In addition, the inclusion of the highly electropositive A+ cations affords a band gap ranging from 3.10 to 3.37 eV, which facilitates the improvement of LIDT (9.3–12.4 × AgGaS2). To the best our knowledge, crystals AGa5S8 (A = K, Rb and Cs) are the first series of ternary A-inclusion chalcogenides with large second-harmonic generation responses (≥1.0 × AgGaS2) and wide band gaps (≥3.0 eV), fulfilling the rigorous requirements of outstanding IR NLO materials. In addition, the “one-for-multiple substitution” strategy presents the great significance of diamondlike structure evolution and provides a remarkable opportunity to achieve NLO materials.

Giant Enhancement and Directional Second Harmonic Emission from Monolayer WS2 on Silicon Substrate via Fabry-Pérot Micro-Cavity.

Two-dimensional transition metal dichalcogenides (TMDs) possess large second-order optical nonlinearity, making them ideal candidates for miniaturized on-chip frequency conversion devices, all-optical interconnection, and optoelectronic integration components. However, limited by subnanometer thickness, the monolayer TMD exhibits low second harmonic generation (SHG) conversion efficiency (<0.1%) and poor directionality, which hinders their practical applications. Herein, we proposed a Fabry-Pérot (F-P) cavity formed by coupling an atomically thin WS2 film with a silicon hole matrix to enhance the SH emission. A maximum enhancement (∼1580 times) is achieved by tuning the excitation wavelength to be resonant with the microcavity modes. The giant enhancement is attributed to the strong electric field enhancement in the F-P cavity and the oscillator strength enhancement of excitons from suspended WS2. Moreover, directional SH emission (divergence angle ∼5°) is obtained benefiting from the resonance of the F-P microcavity. Our research results can provide a practical sketch to develop both high-efficiency and directional nonlinear optical devices for silicon-based on-chip integration optics.

Surface functionalization of Si6Li6 cluster with superalkalis to achieve high nonlinear optical response: A DFT study

In this study, the nonlinear optical (NLO) response of pure and superalkali (Li3O, Na3O, and K3O) doped Si6Li6 clusters has been explored. The doping of superalkalis on the Si6Li6 cluster significantly narrowed the wide HOMO-LUMO energy gap (5.27 eV) of the pure Si6Li6 cluster up to 3.83 eV. All superalkali doped clusters reveal electride nature based on the HOMOs’ electron density. The thermodynamic stability of these electrides is anticipated through their interaction energies with the highest value (3.90 eV) for Si6Li6-Li3O. The NLO properties of superalkali doped Si6Li6 electrides are investigated through first and second-order hyperpolarizabilities. These complexes exhibit large first hyperpolarizabilities as compared to pristine Si6Li6. Among superalkali doped clusters, Si6Li6-K3O showed the highest first hyperpolarizability of 1.42 × 104 au. The small crucial excitation energies are responsible for such a high NLO response. For dynamic NLO response, electro-optic Pockel’s effect and second harmonic generation are calculated. A very large quadratic NLO response (3.61 ×10−9 au) is observed for the Si6Li6-Li3O complex. The quantum theory of atoms in molecules (QTAIM) analysis shows the electrostatic interaction between interacting species. All the electrides exhibit ultrahigh transparency in the UV–VISIBLE region. These intriguing results are self-serving to promote promising applications of Si6Li6-based clusters in high-performance nonlinear optical materials.

Large third-order optical nonlinearities of two-dimensional CsPbBr3 nanoplatelets

Metal halide perovskites show considerable optical nonlinearity and could be used for cost-effective nonlinear optical devices if their nonlinear susceptibilities can be improved. Here, we report large optical nonlinearity, including third-order nonlinear absorption, refraction, and two-photon absorption excited luminescence, of CsPbBr3 nanoplatelets with a thickness of two or three atomic layers and a plane size of about 60 nm. Specifically, the nonlinear absorption was mainly induced by two-photon absorption at low incident powers, and the nonlinear absorption cross section reached 2.15 × 107 GM. It is two orders of magnitude larger than that of CsPbBr3 nanocrystals, which makes them an ideal optical limiting material. Furthermore, the nanoplatelets exhibited large self-phase modulation-induced nonlinear refraction, and the figures of merit W and T satisfied W &amp;gt;1 and T &amp;lt;1, which allow for optical switching. The large optical nonlinearity of CsPbBr3 nanoplatelets provides a basis for multifunctional applications in nonlinear optical devices.

Mixed-Anion-Oriented Design of LnMGa3S6O (Ln = La, Pr, and Nd; M = Ca and Sr) Nonlinear Optical Oxysulfides with Targeted Property Balance

Nonlinear optical (NLO) crystals are of importance on extending infrared (IR) laser wavelengths. Considering their performance drawbacks in commercial IR NLO crystals, a recent challenge in exploring new excellent IR NLO crystals is how to break the inherent conflict between a wide bandgap (Eg ≥ 3.0 eV) and large NLO effect (dij ≥ 0.5 × AgGaS2) and simultaneously enlarge the birefringence (Δn) for a requisite phase-matching (PM) behavior. For that reason, rational combination of mixed-anion functional groups into a crystal structure affords the successful design and synthesis of six LnMGa3S6O (Ln = La, Pr, and Nd; M = Ca and Sr) NLO oxysulfides. Among them, LaMGa3S6O satisfy the property-balance demand (Eg: 3.21-3.27 eV and dij: 0.9-1.0 × AgGaS2) as promising PM NLO crystals through gathering their property advantages between LaMGa3O7 and LaMGa3S7 by mixed-anion-oriented performance engineering. A study on the structure-property relationship indicates that heteroleptic (Ln/M)S7O and GaS3O anionic groups are proven as promising NLO-active units and offer a great synergistic effect on the NLO origin. This work as a visualized model not only provides a first clear cognition on varying properties from oxide to sulfide to oxysulfide but also highlights the feasibility of mixed-anion-oriented design of new NLO candidates with balanced performances.

Nonlinear optical properties of Bi0.5Na0.5TiO3 thin films grown by PLD

The present work investigates the role of oxygen partial pressure (PO2) during the thin film growth in obtaining phase and controlling the crystallinity and optical responses in the thin films. Rietveld refinement of X-ray diffraction confirmed a rhombohedral structure of BNT as a major phase with secondary phase of Bi2Ti2O7 and Bi4Ti3O12. The diminutions of the secondary phase are observed with an increase in PO2, which signifies the crystal structure closely related to the partial oxygen pressure. The refractive index of films was found to be improved and optical bandgap energy was reduced with PO2 due to the increase in crystallinity as well as decrease in oxygen vacancies. Nonlinear optical properties show a strong PO2 dependency, self-focusing behaviour with a positive, large optical nonlinearity (n2 = 4.62 × 10−6 cm2/W) and strong absorbance (β = 0.755 cm/W) for the film deposited at 10 Pa, which makes a potential candidate for the nonlinear photonic device applications.