Strong Second Harmonic Generation Response Research Articles

K2Sb(P2O7)F: Cairo Pentagonal Layer with Bifunctional Genes Reveal Optical Performance

Discovering new functional genes, designing perfect crystal structures, and developing high-performance materials are the goals being pursued by scientists. Herein, the first antimony pyrophosphate, K2 Sb(P2 O7 )F, possessing an optimal layered structure, is reported, where the perfect structural arrangement induces excellent optical properties. K2 Sb(P2 O7 )F not only displays a sharply enhanced birefringence (0.157@546 nm) compared to the existing phosphate optical materials, but also exhibits a strong second-harmonic generation response (4.0×KDP). Remarkably, a new bifunctional gene, the square-pyramidal SbO4 F group, was discovered, and a unique two-dimensional arrangement of Cairo pentagonal tiling units was observed in inorganic compounds for the first time.

Controllable synthesis and spontaneous phase transition of photonic coordination polymer to produce a strong second-harmonic generation response

Herein, a novel photonic coordination polymer material was constructed by aggregation-induced emission luminogen (AIEgen) containing a tripyridyl moiety used as the linking ligand. It displayed a spontaneous direct centrosymmetric to noncentrosymmetric phase transition in a single crystal. The two crystals, before and after the phase transition, were both controllably synthesized and characterized by single-crystal X-ray diffraction. After being exposed to air, the centrosymmetric metastable phase (1-α) transitioned to a new stable phase with a noncentrosymmetric structure (1-β). Interestingly, the 1-β structure exhibited a strong phase-matching second-harmonic generation (SHG) response, about 4.5 times higher than that of KH2PO4 (KDP). In order to better understand the relationship between the structure and the nonlinear optical properties, the dipole moments were calculated and discussed. Remarkably, the noncentrosymmetric phase with high thermal stability for 1-β retained and improved the initial photoluminescent properties of the AIEgen ligand after the structural phase transition from 1-α, and simultaneously produced the excellent SHG property, which are beneficial for the design and construction of excellent optical materials.

Strong Second Harmonic Generation in a Tungsten Bronze Oxide by Enhancing Local Structural Distortion.

To discover the nonlinear optical (NLO) materials with strong second harmonic generation (SHG), the design of NLO-active molecular units with large polarization is considered as a common strategy. Herein, we propose that the local structural distortion induced with vacancies, apart from the NLO-active units, can be employed to improve the NLO effect in solids as well. Accordingly, a new tungsten bronze (TB) oxide, Pb2(Pb0.15Li0.7□0.15)Nb5O15 (□ representing vacancies), is successfully designed and prepared, which exhibits a strong SHG response of 39 times that of KH2PO4. The detailed analysis reveals that the local structural distortions enhanced by the vacancies in PLN strengthen the local dipole moments of neighboring NbO6 octahedra, and thus significantly prompt the SHG effect. Moreover, a series of new TB compounds with large NLO effects are discovered by this molecular design strategy, which are perspectives for new NLO materials synthesis.

Non-centrosymmetric sulfides A2Ba6MnSn4S16 (A = Li, Ag): syntheses, structures and properties.

Two new penternary compounds, with the chemical formula of A2Ba6MnSn4S16 (A = Li (1), Ag (2)), have been successfully designed and prepared. They are isostructural and feature the same non-centrosymmetric three-dimensional (3D) framework, which comprises SnS4 tetrahedra and distorted (A/Mn)S4 tetrahedra. They both show strong second-harmonic generation (SHG) responses at 2.05 μm laser radiation of 5.1 and 2.7 × AgGaS2, respectively, at a particle size of 30-40 μm. Meanwhile, they exhibit wide band gaps of 2.88 and 2.76 eV, implying that they avoid two-photon absorption and low laser-induced damage thresholds (LIDTs). Furthermore, with Mn2+ cations modulating disordered sites, the two title compounds also possess paramagnetism. Based on the relationship between the structures and properties of the title compounds and related materials, it can be concluded that new materials with attractive properties can be designed and produced by modulating disordered sites with rational cations.

Influences of Ga Doping on Crystal Structure and Polarimetric Pattern of SHG in ZnO Nanofilms.

The second-harmonic generation (SHG) in gallium doped ZnO (GZO) nanofilms was studied. The Ga doping in GZO nanofilms influenced the crystal structure of the films, which affected SHG characteristics of the nanofilms. In our experiments, a strong SHG response was obtained in GZO nanofilms, which was excited by 790 nm femtosecond laser. It was observed that the Ga doping concentrations affected, not only the intensity, but also the polarimetric pattern of SHG in GZO nanofilms. For 5.0% doped GZO films, the SHG intensity increased about 70%. The intensity ratio of SHG between the incident light polarization angle of 90° and 0°changed with the Ga doping concentrations. It showed the most significant increase for 7.3% doped GZO films, with an increased ratio of c/a crystal constants. This result was attributed to the differences of the ratios of d33/d31 (the second-order nonlinear susceptibility components) induced by the crystal distortion. The results are helpful to investigate nanofilms doping levels and crystal distortion by SHG microscopy, which is a non-destructive and sensitive method.

Highly Polarizable Hg2+ Induced a Strong Second Harmonic Generation Signal and Large Birefringence in LiHgPO4.

A new ultraviolet nonlinear optical material, namely LiHgPO4, was synthesized using the mild hydrothermal method. The structure of LiHgPO4 features novel double layers constructed by severely distorted HgO6 octahedra and PO4 tetrahedra, which are further interconnected by LiO4 tetrahedra to form a three-dimensional structure. LiHgPO4 exhibits a very strong second harmonic generation (SHG) response of 11.0 times that of KH2PO4 and a relatively large birefringence (0.068 at 1064 nm) among the reported SHG-active phosphates. Theoretical calculations revealed that the introduction of the Hg2+ in a highly distorted HgO6 octahedral geometry is crucial to produce the strong SHG response and large birefringence.

In situ [2 + 3] cycloaddition synthesis, crystal structures, strong SHG responses and fluorescence properties of three novel Zn coordination polymers

We report on the synthesis of two acentric and one centrosymmetric Zn metal–organic complexes with 3-tetrazolemethyl pyridine spacers obtained in situ by hydrothermal routes. X-ray diffraction structural analysis reveals that they have the same equivalent nodes but with dissimilar topologies. The two acentric frameworks [Zn(Tzmp)Cl]n (1) and ([Zn(Tzmp)Br]n (2), HTzmp = 3-tetrazolemethyl pyridine) are isomorphism which exhibit an acentric 3D framework with (10, 3)-b net called “ths”, while the centrosymmetric complex ([Zn(Tzmp)N3]n (3)) features a distinctive 2D sheet with Shubnikov hexagonal plane net. Photo-luminescent studies suggest the ligand-field strength of coordinated negative ions (Cl− > Br− > N3−) has ordered adjusting effects on the emission redshift. The second harmonic generation (SHG) measurement shows that compounds 1 and 2 are nonlinear optically active, with SHG responses being 2/3 and half of the standard potassium dihydrogen phosphate (KDP), respectively.

Large Second Harmonic Generation (SHG) Effect and High Laser‐Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide

AbstractA big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59–25 μm is also significantly wider than that of AGS (ca. 0.48–≈11.4 μm). The occurrence of the strong SHG responses and good phase‐matching indicate that the structure of the new Ga2Se3 phase can only be non‐centrosymmetric and have a lower symmetry than the cubic γ‐phase. The observed excellent SHG and phase‐matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

Large Second Harmonic Generation (SHG) Effect and High Laser-Induced Damage Threshold (LIDT) Observed Coexisting in Gallium Selenide.

A big challenge for nonlinear optical (NLO) materials is the application in high power lasers, which needs the simultaneous occurrence of large second harmonic generation (SHG) and high laser induced damage threshold (LIDT). Herein we report the preparation of a new Ga2 Se3 phase, which shows the SHG intensities of around 2.3 times and the LIDT of around 16.7 times those of AgGaS2 (AGS), respectively. In addition, its IR transparent window ca. 0.59-25 μm is also significantly wider than that of AGS (ca. 0.48-≈11.4 μm). The occurrence of the strong SHG responses and good phase-matching indicate that the structure of the new Ga2 Se3 phase can only be non-centrosymmetric and have a lower symmetry than the cubic γ-phase. The observed excellent SHG and phase-matching properties are consistent with our diffraction experiments and can be well explained by using the orthorhombic models obtained through our high throughput simulations.

CsSbF2SO4: An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO4 (KTP)‐type Structure

AbstractA novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF2SO4, was obtained by ionothermal synthesis. A meticulously designed co‐substitution approach was used to successfully replace the [TiO6]8− and [PO4]3− functional groups in KTiOPO4 (KTP) with [SbO4F2]7− and [SO4]2− units, respectively. The structure of CsSbF2SO4 features a pseudo‐3D framework consisting of interconnected 1D [SbF2O2SO4]5− chains of corner‐sharing [SbO4F2]7− octahedra and [SO4]2− tetrahedra. The title compound exhibits a sharply enlarged band gap compared to its parent compound, KTP, benefitting from the introduction of F− ions and the displacement of Sb3+ cations. Second harmonic generation (SHG) measurements manifested that CsSbF2SO4 is phase‐matchable and revealed a strong SHG response of about 3.0 KH2PO4 (KDP), which is the highest value reported for any metal sulfate reported to date. The reported fluoride sulfate is a promising near ultraviolet (UV) nonlinear optical (NLO) material.

CsSbF2 SO4 : An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO4 (KTP)-type Structure.

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF2 SO4 , was obtained by ionothermal synthesis. A meticulously designed co-substitution approach was used to successfully replace the [TiO6 ]8- and [PO4 ]3- functional groups in KTiOPO4 (KTP) with [SbO4 F2 ]7- and [SO4 ]2- units, respectively. The structure of CsSbF2 SO4 features a pseudo-3D framework consisting of interconnected 1D [SbF2 O2 SO4 ]5- chains of corner-sharing [SbO4 F2 ]7- octahedra and [SO4 ]2- tetrahedra. The title compound exhibits a sharply enlarged band gap compared to its parent compound, KTP, benefitting from the introduction of F- ions and the displacement of Sb3+ cations. Second harmonic generation (SHG) measurements manifested that CsSbF2 SO4 is phase-matchable and revealed a strong SHG response of about 3.0 KH2 PO4 (KDP), which is the highest value reported for any metal sulfate reported to date. The reported fluoride sulfate is a promising near ultraviolet (UV) nonlinear optical (NLO) material.

Phase Identification and Strong Second Harmonic Generation in Pure ε-InSe and Its Alloys.

Two-dimensional material indium selenide (InSe) has offered a new platform for fundamental research in virtue of its emerging fascinating properties. Unlike 2H-phase transition-metal dichalcogenides (TMDs), ε phase InSe with a hexagonal unit cell possesses broken inversion symmetry in all the layer numbers, and predicted to have a strong second harmonic generation (SHG) effect. In this work, we find that the as-prepared pure InSe, alloyed InSe1- xTe x and InSe1- xS x ( x = 0.1 and 0.2) are ε phase structures and exhibit excellent SHG performance from few-layer to bulk-like dimension. This high SHG efficiency is attributed to the noncentrosymmetric crystal structure of the ε-InSe system, which has been clearly verified by aberration-corrected scanning transmission electron microscopy (STEM) images. The experimental results show that the SHG intensities from multilayer pure ε-InSe and alloyed InSe0.9Te0.1 and InSe1- xS x ( x = 0.1 and 0.2) are around 1-2 orders of magnitude higher than that of the monolayer TMD systems and even superior to that of GaSe with the same thickness. The estimated nonlinear susceptibility χ(2) of ε-InSe is larger than that of ε-GaSe and monolayer TMDs. Our study provides first-hand information about the phase identification of ε-InSe and indicates an excellent candidate for nonlinear optical (NLO) applications as well as the possibility of engineering SHG response by alloying.

Enhanced second harmonic generation by double plasmon resonances in mesoscale flower-like silver particles

We investigate second harmonic generation (SHG) response of mesoscale silver (Ag) particles. The flower-like Ag mesoparticles and Ag micro-hemispheres on an indium tin oxide coated glass substrate were prepared by a simple electrochemical deposition method. We find that the mesoscale Ag particles show a strong SHG response associated with their geometries. The dependence of the SHG on the excitation wavelength reveals that the multi-resonant response occurring at the emission wavelengths plays an important role in SHG enhancement.

Zn3P2S8: A Promising Infrared Nonlinear-Optical Material with Excellent Overall Properties

The thiophosphate Zn3P2S8 is reported for its potential application in infrared (IR) nonlinear optics. This nondeliquescent compound features a cubic closet packing of the (PS4)3- groups, with Zn2+ filling in three-quarters of the tetrahedral interspaces. The optical band gap of Zn3P2S8 is characterized as 3.12 eV, which is very beneficial to improving the laser damage threshold. Besides, Zn3P2S8 demonstrates good phase matchability (PM)with a strong second-harmonic-generation (SHG) response that is about 2.6 times that of AgGaS2, achieving a valuable balance among good phase matchability, strong SHG response, and large optical band gap. The origin of these attractive optical properties is investigated in detail via theoretical calculations. Moreover, the differential scanning calorimetry curve indicates a congruent-melting thermal behavior of Zn3P2S8, which is conducive to large single-crystal growth. The excellent comprehensive performance of Zn3P2S8 makes it a practically usable IR nonlinear-optical candidate.

Tailoring nonlinear optical crystal borophosphate through the introduction of transition metal d orbitals for improving optical anisotropy and SHG response: a first-principles investigation

Motivated by the discovery of practical and economical nonlinear optical (NLO) materials with strong second harmonic generation (SHG), experimental and theoretical researches have been widely carried out. However, drawbacks in one or some respects, especially poor birefringence, preclude their use for NLO applications in optoelectronic technologies. In the present work, taking the case of nonlinear material borophosphate BPO4, a systematic calculation of the structure, electronic, linear and nonlinear optical properties of the BP1−xVxO4 systems (x = 0, 0.25, 0.5, 0.75, and 1) are presented to tailor its small birefringence and assess their ultraviolet NLO capabilities based on first-principles calculations. Particularly, birefringences of the four V-containing compounds are significantly enhanced to fulfill the phase matching conditions in the ultraviolet region. Meanwhile, their SHG responses are greatly improved, especially for BP0.5V0.5O4, with moderate optical anisotropy of refraction (about 0.08 in transparent regions) and strong second harmonic generation response (almost ten times as compared with BPO4). Besides, a detailed analysis of their electronic characters, the polarizability anisotropy and local dipole moments of asymmetry functional building [BO4]5−, [PO4]3−, and [VO4]3− units are elucidated to understand the high performance of BP1−xVxO4 systems. These candidates would extend the ultraviolet nonlinear optical materials. Furthermore, the strategy of introducing transition metal d orbitals could be a promising way to tailor electronic structures and optical anisotropy in other functional materials for advanced photonic devices.

Rb3VO(O2)2CO3: A Four‐in‐One Carbonatoperoxovanadate Exhibiting an Extremely Strong Second‐Harmonic Generation Response

AbstractA nonlinear optical (NLO) carbonatoperoxovanadate, Rb3VO(O2)2CO3, was synthesized through a simple solution‐evaporation method in phase‐pure form. Single‐crystal X‐ray diffraction revealed that the structure of Rb3VO(O2)2CO3 consists of important noncentrosymmetric (NCS) chromophores, that is, π‐delocalized (CO3)2− groups, a second‐order Jahn–Teller (SOJT) distortive V5+ cation, and π‐localized distorted O22− groups, as well as charge‐balancing polarizable Rb+ ions. The powder second‐harmonic generation (SHG) measurements indicated that Rb3VO(O2)2CO3 is phase‐matchable (Type I) and exhibits a remarkably strong SHG response circa 21.0 times that of potassium dihydrogen phosphate (KDP), which is the largest efficiency observed among carbonate NLO materials. First‐principles calculation analysis suggests that the extremely large SHG response of Rb3VO(O2)2CO3 is attributed to the synergistic effect of the cooperation of all the constituting NCS chromophores.

Rb3 VO(O2 )2 CO3 : A Four-in-One Carbonatoperoxovanadate Exhibiting an Extremely Strong Second-Harmonic Generation Response.

A nonlinear optical (NLO) carbonatoperoxovanadate, Rb3 VO(O2 )2 CO3 , was synthesized through a simple solution-evaporation method in phase-pure form. Single-crystal X-ray diffraction revealed that the structure of Rb3 VO(O2 )2 CO3 consists of important noncentrosymmetric (NCS) chromophores, that is, π-delocalized (CO3 )2- groups, a second-order Jahn-Teller (SOJT) distortive V5+ cation, and π-localized distorted O22- groups, as well as charge-balancing polarizable Rb+ ions. The powder second-harmonic generation (SHG) measurements indicated that Rb3 VO(O2 )2 CO3 is phase-matchable (Type I) and exhibits a remarkably strong SHG response circa 21.0 times that of potassium dihydrogen phosphate (KDP), which is the largest efficiency observed among carbonate NLO materials. First-principles calculation analysis suggests that the extremely large SHG response of Rb3 VO(O2 )2 CO3 is attributed to the synergistic effect of the cooperation of all the constituting NCS chromophores.

Strong SHG Response via High Orientation of Tetrahedral Functional Motifs in Polyselenide A2Ge4Se10 (A = Rb, Cs)

AbstractNonlinear optical (NLO) materials with strong second harmonic generation (SHG) responses are technologically and scientifically important for tunable lasers. This work puts forward a new strategy for designing promising infrared nonlinear optical (IR‐NLO) materials with strong SHG responses by strengthening both the static and induced contributions via the high orientation of NLO functional motifs. Two new polyselenides Rb2Ge4Se10 and Cs2Ge4Se10 are studied to verify the strategy, they have 2D infinite [Ge4Se10]2− layers comprising highly oriented distorted GeSe4 tetrahedra. Their large SHG signals (8.0 and 8.5 times that of commercial AgGaS2) can be ascribed to both the static contribution enhancement from the high orientation of the local dipole moment of GeSe4 tetrahedra and the induced contribution enhancement from terminal and SeSe bonded Se atoms. The results confirm the effectiveness of the proposed approaches, shedding light on the exploration of practical IR‐NLO materials with maximized performance.

Li7 Cd4.5 Ge4 Se16 and Li6.4 Cd4.8 Sn4 Se16 : Strong Nonlinear Optical Response in Quaternary Diamond-Like Selenide Networks.

Two new selenides with diamond-like structures, Li7 Cd4.5 Ge4 Se16 and Li6.4 Cd4.8 Sn4 Se16 , were synthesized by using a conventional high-temperature solid-state reaction method. They crystallize in the space group Pna21 (no. 33) of the orthorhombic system. Their three-dimensional frameworks consist of corner-sharing LiSe4 , CdSe4 , and MSe4 (M=Ge, Sn) tetrahedra. These two compounds exhibit strong powder second-harmonic generation responses that are about 1.2 and 2.5 times that of the benchmark AgGaS2 at a laser wavelength of λ=2.09 μm, and also demonstrate type I phase-matchable behavior. The optical bandgaps were determined to be 2.18 and 1.95 eV for Li7 Cd4.5 Ge4 Se16 and Li6.4 Cd4.8 Sn4 Se16 , respectively. Furthermore, these two materials exhibit congruent melting behavior at rather low temperatures of 985 and 1060 K, respectively, which makes bulk single crystal growth by using the Bridgman-Stockbarger method possible. Our study indicates that these two materials show advantages over the traditional IR NLO material CdSe and are promising for practical applications.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.