New Nonlinear Optical Research Articles

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.

Growth of the new high-performance NLO crystal BaGa2GeSe6 via the controlled vapor pressure method

BaGa2GeSe6, a new nonlinear optical (NLO) crystal with various advantages, has important applications in environmental monitoring, medical diagnosis, infrared countermeasures and some other areas. In this paper, the high purity polycrystalline charges were synthesized by two-temperature-zone method. Using synthesized polycrystal, BaGa2GeSe6 single crystals with size of Ф15mm × 50 mm were grown successfully by the controlled vapor pressure method (CVP) for the first time. As large as 6 × 10 × 21 mm3 sample was fabricated from the as-grown crystal. The BaGa2GeSe6 crystal was characterized and analyzed by thermal analysis, chemical composition, and transmission spectra etc. A new method was provided to grow the new high-performance crystal BaGa2GeSe6, and it is meaningful for preparing other similar crystals.

LnLiSiS4 (Ln = La and Ce): Promising infrared nonlinear optical materials designed by aliovalent substitution from SrCdSiS4

Aliovalent substitution is an effective route to design new nonlinear optical (NLO) crystals. Using SrCdSiS4 as a parent compound, two new infrared NLO lanthanide thiosilicates, namely LnLiSiS4 (Ln = La and Ce), have been successfully obtained through aliovalent substitution. Interestingly, these compounds exhibit [LiSiS4]3- layers composed of vertex- and edge-shared LiS4 and SiS4 tetrahedra that significantly different from the [LnSiS4]3- layers composed of edge-shared LnS6 trigonal prisms (or LnS7 monocapped trigonal prisms) and SiS4 tetrahedra in other ALnSiS4 (A = K, Rb, Cs, Ln = lanthanide) compounds with larger sized alkali cations. LnLiSiS4 (Ln = La and Ce) also achieve balanced properties for good infrared NLO materials: largest SHG response among all known thiosilicates (2.0 and 2.1 × AgGaS2 @ 2 μm for LaLiSiS4 and CeLiSiS4 respectively) with phase matching ability, high laser induced damage threshold (14 and 9 times of AgGaS2), wide bandgap (3.71 and 2.92 eV), wide infrared transmission range (0.35–18 μm) and good thermal stability above 700 °C. This work not only enriches the structure chemistry of lanthanide thiosilicates, but also provides an efficient route to design new high performance IR NLO materials.

A theoretical exploration of the second-order NLO properties of linked sandwich double-layered metallacarboranes: charge transfer mediated by linker groups.

Hetero-bimetallic organic compounds have great potential for the development of new nonlinear optical (NLO) materials, due to their large first hyperpolarizabilities (βtot). Herein, due to their versatility and ease of functionalization, the second-order NLO properties of a series of linked sandwich metallacarboranes were studied by changing their linkages to different organic groups. The calculated βtot values suggest that the NLO response was significantly enhanced when an alkenyl group of appropriate length was inserted into the B-B or C-C bonds connecting the metallacarborane units. Time-dependent density-functional theory was used to explain how the connection modes and the use of organic groups as linkers can give rise to different types of charge transfer. Moreover, the NLO responses of the redox states (+1 and -1) were calculated, with the aim of investigating the NLO switching effects of the -1/0/+1 states. Comparison of the βtot values for the different states shows that the studied linked sandwich metallacarboranes could serve as three-state NLO molecular switches stimulated by redox processes.

(C4H10NO)PbX3 (X = Cl, Br): Design of Two Lead Halide Perovskite Crystals with Moderate Nonlinear Optical Properties.

Introducing electronegative species into organic constituents was considered to be one effective strategy for adjusting crystal symmetry and designing new nonlinear optical (NLO) materials. By substitution of C4 in piperidine (C5H11N) with electronegative oxygen, organic morpholine (C4H9NO) was easily obtained. Therefore, to design NLO crystals, we focused on combinations of stereochemically active lone-pair (SCALP) cation (Pb2+)-based chloride and bromide with morpholine molecules. In this work, two lead halide hybrid perovskite (C4H10NO)PbX3 (X = Cl, Br, abbreviated as MPbCl3 and MPbBr3, respectively) single crystals with moderate nonlinear optical properties were synthesized by a slow evaporation method. The two title crystals belong to orthorhombic space group P212121 with one-dimensional (1D) chainlike perovskite structures. Theoretical calculations revealed that the second harmonic generation (SHG) responses mainly originate from distorted {PbX6} octahedrons of the inorganic framework. Remarkably, moderate phase-matching SHG effects of about 0.70 and 0.81 times KH2PO4, large birefringences of 0.098 and 0.111 at 1064 nm, and large laser damage thresholds (LDTs) of 19.94 and 46.82 MW/cm2 were estimated for MPbCl3 and MPbBr3, respectively. This work provides a novel strategy for new purpose-designed hybrid NLO crystals by adjustment and modulation of chemical modification.

Pr:LGSB as a new nonlinear optical crystal: Czochralski growth and optical characterization

Herein, we report on the Czochralski growth and optical characterization of Pr:LGSB as a new nonlinear optical (NLO) and laser crystal. Single crystals of Pr:LGSB were grown by the Czochralski method, for the first time to the best of our knowledge, from the starting melt compositions La 0.656 Pr 0.022 Gd 0.572 Sc 2.75 (BO 3 ) 4 and La 0.651 Pr 0.027 Gd 0.572 Sc 2.75 (BO 3 ) 4 . The crystal growth parameters were optimized and two Pr:LGSB crystals with good optical quality were obtained. The chemical compositions of the grown crystals were determined to be La 0.750 Pr 0.020 Gd 0.450 Sc 2.780 (BO 3 ) 4 and La 0.743 Pr 0.025 Gd 0.452 Sc 2.780 (BO 3 ) 4 corresponding to a Pr 3+ ions concentration in the crystals of 2.0 at% and 2.5 at%, respectively. The spectroscopic properties were investigated and the obtained results show that the 2.5 at% Pr:LGSB is a promising laser crystal emitting in the orange spectral range at ~ 603 nm. The refractive indices were measured and the phase-matching curves for type I and type II SHG were determined. The walk-off angle, the external angular acceptance, and the nonlinear coefficient d 11 for type I SHG of 603 nm fundamental wavelength were also evaluated. This work shows that the 2.5 at% Pr:LGSB crystal could be a new promising candidate for obtaining laser sources in the UV range (~ 301.5 nm) in SFD configuration. • Pr:LGSB crystal were grown by the Czochralski method for the first time. • Spectroscopic and NLO properties of the 2.5 at% Pr:LGSB crystal are presented. • 2.5 at% Pr:LGSB has promising properties for laser emission in the orange domain. • Phase-matching curves for type I and type II SHG are determined. • Preliminary prospects for SFD in the UV domain were analyzed.

Sr3[SnOSe3][CO3]: A Heteroanionic Nonlinear Optical Material Containing Planar π‐conjugated [CO3] and Heteroleptic [SnOSe3] Anionic Groups

AbstractInorganic heteroanionic materials are attracting increasing attention for exploring new nonlinear optical (NLO) materials because they could better satisfy the necessary but conflicting properties of NLO crystals, e.g. large SHG response and wide band‐gap. Up to now, the reports on heteroanionic NLO materials have mainly focused on ultraviolet or visible oxide‐based fluoroborates, fluorophosphates, borate‐phosphates and borate‐iodates. However, chalcogenides containing different kinds of anionic groups have barely been reported. Herein, we have synthesized the first oxychalcogenide‐carbonate, Sr3[SnOSe3][CO3] that contains two different kinds of anionic groups, [SnOSe3] and [CO3]. It crystallizes in a noncentrosymmetric space group and exhibits fascinating NLO properties, including a large SHG response (≈1×AGS), sufficient birefringence (0.12 @1064 nm), wide band‐gap (3.46 eV) and high laser damage threshold (240 MW cm−2). These make Sr3[SnOSe3][CO3] a promising NLO crystal.

Sr3[SnOSe3][CO3]: A Heteroanionic Nonlinear Optical Material Containing Planar π‐conjugated [CO3] and Heteroleptic [SnOSe3] Anionic Groups

AbstractInorganic heteroanionic materials are attracting increasing attention for exploring new nonlinear optical (NLO) materials because they could better satisfy the necessary but conflicting properties of NLO crystals, e.g. large SHG response and wide band‐gap. Up to now, the reports on heteroanionic NLO materials have mainly focused on ultraviolet or visible oxide‐based fluoroborates, fluorophosphates, borate‐phosphates and borate‐iodates. However, chalcogenides containing different kinds of anionic groups have barely been reported. Herein, we have synthesized the first oxychalcogenide‐carbonate, Sr3[SnOSe3][CO3] that contains two different kinds of anionic groups, [SnOSe3] and [CO3]. It crystallizes in a noncentrosymmetric space group and exhibits fascinating NLO properties, including a large SHG response (≈1×AGS), sufficient birefringence (0.12 @1064 nm), wide band‐gap (3.46 eV) and high laser damage threshold (240 MW cm−2). These make Sr3[SnOSe3][CO3] a promising NLO crystal.

Band gap modulation and nonlinear optical properties of quaternary tellurates Li2GeTeO6.

Tellurate crystals are attractive for developing new nonlinear optical (NLO) materials in the mid-infrared region due to their wide transmission window. In this work, we report a quaternary tellurate oxide crystal, Li2GeTeO6, which exhibits a short cutoff edge (240 nm) with a powder second harmonic generation (SHG) response of 1.3 × KH2PO4 (KDP). The reported material reveals the largest band gap in the Li2MTeO6 (M = tetravalent cation) family. The first-principles calculations were used to illustrate the origin of the NLO effect. These results highlight the band gap engineering based on the cation substitution strategy for designing new NLO materials with balanced optical properties.

Rational combination of multiple structural groups on regulating nonlinear optical property in hexagonal Ln3MGeS7 polar crystals

Combination of multiple structural groups was developed as one effective method for regulating material property and exploring new nonlinear optical (NLO) crystals. For that reason, four Ln3MGeS7 (Y3LiGeS7, Y3Cd0.5GeS7, Gd3Cd0.5GeS7 and Sm3Zn0.5GeS7) crystals with various structural motifs were successfully synthesized and systematically investigated. Note that Y3LiGeS7 and Y3Cd0.5GeS7 were firstly synthesized so far. Performance test shows that Ln3MGeS7 compounds exhibit the variable optical bandgaps (1.62–2.33 eV) and good second harmonic generation (SHG) responses (0.7–1.1 × commercial AgGaS2) with requisite phase-matching behavior, which agree well with the theoretical results (Y3LiGeS7: Δn = 0.058 and d33 = 19.97 pm/V; Y3Cd0.5GeS7: Δn = 0.055 and d33 = 20.6 pm/V) and introduction of MIIB (Zn, Cd) atoms into crystal structure is conducive to enlarge the SHG effect. SHG density and dipole-moment calculations indicate that their SHG effects are originated from the major contribution on LnSn units with moderate effect of GeS4 and MIIBS6 (Zn, Cd) ligands. Therefore, selecting appropriate functional motifs (LnSn and MIIB) into crystal structure can promote the enhancement of NLO property and further realize the rational design of new promising infrared NLO materials.

Fine-Tuning of Nonlinear Optical Contrasts of Hexaphyrin-Based Molecular Switches Using Inverse Design.

In the search for new nonlinear optical (NLO) switching devices, expanded porphyrins have emerged as ideal candidates thanks to their tunable chemical and photophysical properties. Introducing meso-substituents to these macrocycles is a successful strategy to enhance the NLO contrasts. Despite its potential, the influence of meso-substitution on their structural and geometrical properties has been scarcely investigated. In this work, we pursue to grasp the underlying pivotal concepts for the fine-tuning of the NLO contrasts of hexaphyrin-based molecular switches, with a particular focus on the first hyperpolarizability related to the hyper-Rayleigh scattering (β HRS ). Building further on these concepts, we also aim to develop a rational design protocol. Starting from the (un)substituted hexaphyrins with various π-conjugation topologies and redox states, structure-property relationships are established linking aromaticity, photophysical properties and β HRS responses. Ultimately, inverse molecular design using the best-first search algorithm is applied on the most favorable switches with the aim to further explore the combinatorial chemical compound space of meso-substituted hexaphyrins in search of high-contrast NLO switches. Two definitions of the figure-of-merit of the switch performance were used as target objectives in the optimization problem. Several meso-substitution patterns and their underlying characteristics are identified, uncovering molecular symmetry and the electronic nature of the substituents as the key players for fine-tuning the β HRS values and NLO contrasts of hexaphyrin-based switches.

Coordination-Directed Structural Modulation and Design of Deep-Ultraviolet Nonlinear Optical Materials

The exploration of new nonlinear optical (NLO) materials which can realize the balance between deep-ultraviolet (UV) transparency and large NLO response is still urgently needed owing to their abil...

Tin Metal Cluster Compounds as New Third-Order Nonlinear Optical Materials by Computational Study.

It is quite appealing but challenging to predict and synthesize new nonlinear optical (NLO) materials with exceptional performance. Herein, the different Sn4 cluster core structures and third-order NLO properties are studied through electronic structure, excited hole-electron, bonding character, and aromaticity analysis. As a result, Sn4 clusters with ring core structure (Sn4-R) not only have the smallest Egap, the largest UV-vis response intensity, but also the strongest third-order NLO response in our work. As proved by natural bond orbitals' (NBO) analysis, electron localization function (ELF), and adaptive natural density partitioning (AdNDP), the Sn44+ has two in-plane four center-two electron (4c-2e) Sn-Sn σ-bonds, resulting in a good delocalization. For the first time, delocalization of metal cluster cores in tin clusters that is beneficial to the third-order NLO response is proposed, which provides a new guidance to design and prepare third-order NLO materials.

KCs2[Pb2Br5(HCOO)2]: A Polar 3D Lead‐Bromide Framework Exhibiting Strong Second‐Harmonic Generation Response

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs2 [Pb2 Br5 (HCOO)2 ], which has been synthesized by a mix-solvothermal method. KCs2 [Pb2 Br5 (HCOO)2 ] exhibits strong phase-matching second-harmonic generation (SHG) response (6.5×KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs2 [Pb2 Br5 (HCOO)2 ] features a polar 3D lead-bromide framework in which adjacent Pb-Br layers containing coplanar Pb6 Br6 rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.

Be2(BO3)(IO3): The First Anion‐mixed Van der Waals Member in the KBe2BO3F2 Family with a Very Strong Second Harmonic Generation Response

AbstractTo obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate‐iodate NLO crystal, Be2(BO3)(IO3) (BBIO), by multicomponent modification of KBe2BO3F2 (KBBF), in which the structural features of KBBF were maintained and (IO3)− groups were connected to honeycomb [Be2BO3O2]∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO3)−, (BO3)3− and (BeO4)6− groups, and exhibited a very strong SHG response of ≈7.2×KH2PO4 (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate‐iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Be2 (BO3 )(IO3 ): The First Anion-mixed Van der Waals Member in the KBe2 BO3 F2 Family with a Very Strong Second Harmonic Generation Response.

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate-iodate NLO crystal, Be2 (BO3 )(IO3 ) (BBIO), by multicomponent modification of KBe2 BO3 F2 (KBBF), in which the structural features of KBBF were maintained and (IO3 )- groups were connected to honeycomb [Be2 BO3 O2 ]∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO3 )- , (BO3 )3- and (BeO4 )6- groups, and exhibited a very strong SHG response of ≈7.2×KH2 PO4 (KDP, @1064 nm) and a large birefringence (Δn) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate-iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.

Sr2Pb(BeB5O10)(BO3): An Excellent Ultraviolet Nonlinear-Optical Beryllium Borate by the Pb-Modified Construction of a Conjugated System and Lone-Pair Effect.

The design of material by chemical and/or crystalline modification of a classic structure model benefits not only the optimized physical properties but also the controllability and efficiency. Herein, a new nonlinear-optical (NLO) beryllium borate crystal, Sr2Pb(BeB5O10)(BO3) (SPBBO), is successfully designed and synthesized by chemical and crystalline modification of the perovskite-like K3B6O10Cl NLO crystal. SPBBO displays a 3D BeB5O103- open-framework structure composed of interconnecting BeB5O13 groups with filled cationic Sr/Pb and anionic BO3 groups, which exhibits the striking enhancement of the second-harmonic-generation (SHG) response (8 × KDP) and birefringence (0.10) compared to the parent model. Replacement of K by Sr and Pb with a lone pair and replacement of Cl by conjugated BO3 result in the synergistic conjugation of Pb with host BeB5O103- and filled BO3 groups, contributing to the striking enhancement of the SHG and birefringence. Single-crystal measurements show that SPBBO has a short UV absorption edge of 280 nm with a wide energy band gap of 4.35 eV and an outstanding laser-induced resistant behavior with a remarkably high laser-induced damage threshold of 2100 MW cm-2. The excellent properties indicate that the SPBBO crystal is a very promising UV NLO functional material.

Unique Unilateral-Chelated Mode-Induced d–p−π Interaction Enhances Second-Harmonic Generation Response in New Ln3LiMS7 Family

Multiple chelated configurations of anionic groups offer a great chance to design new nonlinear optical (NLO) materials with excellent performances for infrared (IR) application. In this work, the new polar Ln3LiMS7 (Ln = rare-earth; M = Ge, Sn) family as promising IR NLO candidates were successfully designed and synthesized by the unique close-ring combination between LnS8 and MS4 ligands. Note that La3LiGeS7 and La3LiSnS7 exhibit the good NLO effects (0.7 vs 1.2 × benchmark AgGaS2) with phase-matching behavior and high laser damage thresholds (6.0 vs 2.5 × AgGaS2), respectively. First-principles calculation indicates that their NLO effects originate from the synergistic effect of intrinsic dipole moments and d–p delocalized-π electron-induced dipole oscillations in the Ln3LiMS7 family. This result also verifies that unique unilateral-chelated configuration induced d–p−π interactions are beneficial to improve the NLO performances, which offers us one feasible way (incorporation of Ln-centered ligands into crystal structure) to design new promising IR NLO materials.

M(NH2 SO3 )2 (M=Sr, Ba): Two Deep-Ultraviolet Transparent Sulfamates Exhibiting Strong Second Harmonic Generation Responses and Moderate Birefringence.

Over the last few decades, the development of each new nonlinear optical (NLO)-active functional unit has led to the discoveries of a series of excellent NLO materials. In the present work, based on first-principles studies, we identified a novel deep-UV (DUV) NLO-active functional unit, a non-π-conjugated group viz. (NH2 SO3 )- . By combining alkaline-earth metals with (NH2 SO3 )- group, two DUV transparent NLO sulfamates, M(NH2 SO3 )2 (M=Sr, Ba) with superior optical properties including strong SHG responses (1.2 and 2.7 × KH2 PO4 (KDP)), short UV cut-off edge (<190 nm) and moderate birefringence (0.056@589.3 nm for Sr(NH2 SO3 )2 ) were successfully synthesized. Our work has provided not only two promising DUV transparent NLO crystals, but also an innovative non-π-conjugated unit for developing more DUV transparent NLO materials.

M(NH2SO3)2 (M=Sr, Ba): Two Deep‐Ultraviolet Transparent Sulfamates Exhibiting Strong Second Harmonic Generation Responses and Moderate Birefringence

AbstractOver the last few decades, the development of each new nonlinear optical (NLO)‐active functional unit has led to the discoveries of a series of excellent NLO materials. In the present work, based on first‐principles studies, we identified a novel deep‐UV (DUV) NLO‐active functional unit, a non‐π‐conjugated group viz. (NH2SO3)−. By combining alkaline‐earth metals with (NH2SO3)− group, two DUV transparent NLO sulfamates, M(NH2SO3)2 (M=Sr, Ba) with superior optical properties including strong SHG responses (1.2 and 2.7 × KH2PO4 (KDP)), short UV cut‐off edge (&lt;190 nm) and moderate birefringence (0.056@589.3 nm for Sr(NH2SO3)2) were successfully synthesized. Our work has provided not only two promising DUV transparent NLO crystals, but also an innovative non‐π‐conjugated unit for developing more DUV transparent NLO materials.