Ultraviolet Nonlinear Optical Materials Research Articles

LiNaB6O9F2: A Promising UV NLO Crystal Having Fluorine‐Directed Optimal Performances and Double Interpenetrating 3[B6O9F2]∞ Networks

AbstractA long‐lasting challenge in ultraviolet (UV) nonlinear optical (NLO) materials design is to combine conflicting and harsh properties into one structure, including wide UV transparency, strong NLO efficiency, and moderate birefringence to realize phase‐matching at short wavelength. A fluorine‐directed material design strategy is adopted to accelerate the process of finding NLO materials with optimal performances. In this work, taking LiB3O5 (LBO) as a maternal structure, one O atom with two F atoms is substituted and LiNaB6O9F2 which possesses novel double interpenetrating 3[B6O9F2]∞ networks and fluorine‐directed optimal performances including enhanced birefringence and phase‐matching capacity is successfully obtained. The perfect balance among deep‐UV cutoff edge, large second‐harmonic generation (SHG) response (1.1 × KDP), and moderate birefringence (0.067 at 1064 nm) of LiNaB6O9F2 makes it a promising UV NLO crystal.

Phosphites: A Nonlinear Optical Materials System with a Wide Band Gap and Moderate Second-Harmonic Generation Effect

Ultraviolet (UV) nonlinear optical (NLO) materials have crucial practical applications in modern laser science and technology. Phosphates are promising candidates for searching UV NLO materials. However, small optical anisotropy of high-symmetrized (PO4)3- tetrahedron hinders phase matching (PM) in the UV wavelength range. Herein, a low-symmetrized phosphite anionic group (HPO3)2- is proposed as a new NLO-active group that exhibits a larger optical anisotropy and second-harmonic generation (SHG) coefficients than (PO4)3-. Accordingly, two phosphites, (C(NH2)3)2Zn(HPO3)2 and [Al2(HPO3)3(H2O)3]·H2O, that contain (HPO3)2- groups are screened out and synthesized. The UV absorption edges of the two compounds are 6.18 and 6.23 eV, respectively. (C(NH2)3)2Zn(HPO3)2 exhibited an SHG intensity of 1 times that of KDP at 1064 nm. This work proposes a new NLO-active fundamental building unit (FBU) and a new materials system for searching NLO materials.

BaSb(H2PO2)3Cl2: An excellent UV nonlinear optical hypophosphite exhibiting strong second-harmonic generation response

Non π-conjugated tetrahedral groups have emerged as potential basic modules for developing ultraviolet (UV) nonlinear optical materials. However, their intrinsic weak hyperpolarizability and small polarizability anisotropy severely restrict the performance of the designed material. Herein, the first antimony hypophosphite, BaSb(H2PO2)3Cl2, was successfully synthesized via rational design, which exhibits superior nonlinear optical properties including strong second harmonic generation response, appropriate birefringence and wide transmittance, indicating it is a potential UV nonlinear optical material. Remarkably, the title compound exhibits the largest nonlinear optical coefficient (5 × KDP) among all reported antimony-based oxyacid compounds. Detailed theoretical calculations confirmed that its excellent nonlinear optical properties are primarily derived from the ordered [Sb(H2PO2)3Cl2]2- anionic clusters composed of [H2PO2]- pseudo-tetrahedra and [SbO3Cl2]5- distorted polyhedra. This work would extend UV nonlinear optical material system to hypophosphites and lead the further inquiry of new structure-driven functional materials.

Design of a new ultraviolet nonlinear optical material KNO3SO3NH3 exhibiting an unexpected strong second harmonic generation response

Based on the co-crystal engineering strategy, a new polar non-centrosymmetric compound, KNO3SO3NH3, was meticulously designed by introducing KNO3 into the centrosymmetric SO3NH3 crystal. It has an unexpected strong second-harmonic generation (SHG) response (10 × KDP), which is a new record among the inorganic nonlinear optical (NLO) materials without NLO-active cations. Theoretical calculations showed that the enhanced SHG response should be attributed to the effect of hydrogen bond. Meanwhile, it has the shortest absorption edge of 216 nm among the known materials with strong SHG responses (>8 × KDP). Besides, it possesses a large birefringence of 0.096@546 nm. Our results showed that KNO3SO3NH3 should be an excellent UV NLO crystal.

KC9H5O6(H2O): A Promising UV Nonlinear-Optical Material with Large Birefringence Based on a π-Conjugated (C9H5O6)- Group.

In order to meet the growing needs for the laser technology and optics industries, the goal is to find suitable fundamental building blocks with large nonlinear-optical (NLO) coefficients and birefringence for an excellent-performance NLO or birefringent system. Via preliminary investigations and calculations, it has been found that the planar π-conjugated group (C9H5O6)- possesses large polarizability anisotropy (δ) and hyperpolarizability (βmax), comparable to well-known groups such as (B3O6)3-, (C3N3O3)3-, etc. Herein, we report a new alkali-metal 3,5-dicarboxybenzoate, KC9H5O6(H2O) (KH2BTC), which crystallized in the acentric space group Pna21. Second-harmonic-generation (SHG) measurements of KH2BTC under 1064 nm laser radiation show that the SHG response of KH2BTC is 1.2 times that of KDP with type I phase-matching behavior. Birefringence measurements show that KH2BTC owns a large birefringence of about 0.372 at 550 nm. The band gap of KH2BTC obtained by ultraviolet (UV) diffuse-reflectance spectroscopy is 3.91 eV, indicating that KH2BTC has potential applications as UV NLO or birefringent materials. Theoretical calculation further confirmed that the impressive optical properties of KH2BTC are derived from the large polarizability anisotropy of the (C9H5O6)- anions.

Na4B8O9F10: A Deep‐Ultraviolet Transparent Nonlinear Optical Fluorooxoborate with Unexpected Short Phase‐Matching Wavelength Induced by Optimized Chromatic Dispersion

AbstractExploring significant ultraviolet/deep‐ultraviolet nonlinear optical (NLO) materials is hindered by rigorous and contradictory requirements, especially, possessing a moderate optical birefringence to meet phase‐matching (PM). Except for suitable birefringence, small chromatic dispersion is also crucial to blue‐shift the PM wavelength. Here, the introduction of a fluorinated tetrahedral boron‐centred chromophore strategy was proposed to optimize the chromatic dispersion. Herein, the [BF4]− unit with a large HOMO–LUMO band gap was introduced to the Na−B−O−F system and Na4B8O9F10 was designed and synthesized successfully for the first time. Na4B8O9F10 with an optimized chromatic dispersion can achieve a short second harmonic generation PM wavelength of 240 nm with a relatively small birefringence (0.036@1064 nm). Notably, Na4B8O9F10 is the first acentric crystal with [BF4]− units among the reported metal–fluorooxoborate systems, involving isolated [BF4]− and novel [B7O10F6]5− fundamental building blocks.

PO(CH2CH2CF3)3: an organic ultraviolet nonlinear optical material without any anionic group.

Researchers have focused on inorganic compounds to design deep ultraviolet (UV) nonlinear optical (NLO) materials according to anionic group theory, such as CO32−, NO3−, SO42− and PO43− anions. Here we provide a new route to design an UV NLO material using a pure organic compound without any anions. Compound PO(CH2CH2CF3)31, an UV NLO material, has light transmittance up to 83% in the UV spectral region which is larger than most inorganic UV NLO materials. It also displays a wide transparent band, a SHG response of 0.30 × KH2PO4, and a cut-off edge below 200 nm. It displays ladder-like nonlinear optical properties weakened by 1.4 times at around Tc, making compound 1 a potential temperature-controlled UV NLO material. Theoretical analyses reveal that the nonlinear optical properties are primarily due to O-2p, P-2p and F-2p.

Recent Development of Non-π-Conjugated Deep Ultraviolet Nonlinear Optical Materials

Recent Development of Non-π-Conjugated Deep Ultraviolet Nonlinear Optical Materials

NH4Sb2(C2O4)F5: A novel UV nonlinear optical material synthesized in deep eutectic solvents

The deep eutectic solvents was first employed to solve the hydrolysis of Sb3+ cations in Sb(III)-oxyacid system to explore new nonlinear optical materials, producing a novel antimony(III) fluoride oxalate named NH4Sb2(C2O4)F5. The title compound featured a 3D noncentrosymmetric structure composed of [Sb2(C2O4)F5]- anionic clusters and NH4+ cations. The cooperative effect of the planar π-conjugated [C2O4]2- anionic groups and the Sb3+ cations with stereochemically active lone pairs induce a relatively strong SHG response (1.1×KH2PO4) and a large birefringence (0.111@546 nm), which was confirmed by detailed theoretical calculations. The overall performances indicate that NH4Sb2(C2O4)F5 is a potential ultraviolet nonlinear optical material. The successful application of deep eutectic solvents in the synthesis for easy hydrolytic materials system opens the door to exploring new inorganic solid functional materials.

Two Tellurium(IV)-Based Sulfates Exhibiting Strong Second Harmonic Generation and Moderate Birefringence as Promising Ultraviolet Nonlinear Optical Materials.

Two tellurium(IV)-based sulfate nonlinear optical (NLO) materials, Te2O3(SO4) and Te(OH)3(SO4)·H3O, were successfully synthesized via the mild hydrothermal method. Te2O3SO4 has a two-dimensional (2D) structure consisting of [Te6O12]∞ layers as well as [SO4] groups. Te(OH)3(SO4)·H3O features a simple 0D structure made up of an isolated [TeO3] pyramid and a [SO4] tetrahedra. Both of them are phase-matching materials and show remarkable powder second harmonic generation (SHG) efficiencies about 6 and 3 times that of KH2PO4 (KDP), respectively, for Te2O3SO4 and Te(OH)3(SO4)·H3O. Especially for Te(OH)3(SO4)·H3O, in addition to a large SHG response, it possesses a short UV cutoff edge (∼233 nm) as well as moderate birefringence (0.052@546.1 nm). Furthermore, theoretical calculations confirmed that their strong SHG effects are due to the synergistic effect of the [TeO3] pyramid and [SO4] tetrahedra.

CsBaB9O15: a high performance ultraviolet nonlinear optical material activated by the peculiar double layered configuration

CsBaB9O15: a high performance ultraviolet nonlinear optical material activated by the peculiar double layered configuration

Investigations of electronic and nonlinear optical properties of superalkali adsorbed biphenylene based sheets by first-principles calculations

In order to design efficient nonlinear optical materials, in this work, superalkali is adsorbed on biphenylene sheet, where an intramolecular electron donor-acceptor (D-π-A) pair is formed. Theoretical calculation shows that large first hyperpolarizability can be obtained by introducing superalkali into biphenylene sheet. Superalkali modified biphenylene sheet can exhibit considerable the first hyperpolarizability values in the range of 901–2035 au. In addition, we have also studied the adsorption of superalkali on boron doped biphenylene sheet. The results show that the first hyperpolarizability is significantly improved, especially when Li3O is adsorbed on the boron doped plane structure. It is found that the boron-doped biphenylene sheet is better than the pure biphenylene sheet when the superalkali is adsorbed on the plane structure to design the nonlinear optical materials. The results of the visible and ultraviolet spectra show that these systems do not absorb in UV, which indicates that these systems with large first hyperpolarizability may become ultraviolet nonlinear optical materials.

UV Solar‐Blind‐Region Phase‐Matchable Optical Nonlinearity and Anisotropy in a π‐Conjugated Cation‐Containing Phosphate

AbstractWide ultraviolet (UV) transparency, strong second‐harmonic generation (SHG) response, and sufficient optical birefringence for phase‐matching (PM) at short SHG wavelengths are vital for practical UV nonlinear optical (NLO) materials. However, simultaneously optimizing these properties is a major challenge, particularly for metal phosphates. Herein, we report a non‐traditional π‐conjugated cation‐based UV NLO phosphate [C(NH2)3]6(PO4)2⋅3 H2O (GPO) with a short UV cutoff edge. GPO is SHG active at 1064 nm (3.8 × KH2PO4 @ 1064 nm) and 532 nm (0.3 × β‐BaB2O4 @ 532 nm) and also possesses a significant birefringence (0.078 @ 546 nm) with a band gap >6.0 eV. The PM SHG capability of GPO can extend to 250 nm, indicating GPO is a promising UV solar‐blind NLO material. Calculations and crystal structure analysis show that the rare coexistence of wide UV transparency, large SHG response, and optical anisotropy is due to the introduction of π‐conjugated cations [C(NH2)3]+ and their favorable arrangement with [PO4]3− anions.

π-Conjugated Trigonal Planar [C(NH2)3]+ Cationic Group: A Superior Functional Unit for Ultraviolet Nonlinear Optical Materials.

Employing π-conjugated anionic groups in molecular construction has been proven to be an effective strategy to find superior ultraviolet (UV) nonlinear optical (NLO) crystals over the decades. Herein, unlike the traditional π-conjugated anionic groups, we identify that a π-conjugated cationic group, viz., [C(NH2)3]+, is also an excellent UV NLO-active functional group in theory. Furthermore, we identify a [C(NH2)3]+-containing compound, C(NH2)3ClO4, as a promising UV NLO candidate due to its short UV cutoff edge (200 nm), remarkable second-harmonic generation effect (∼3 × KDP), and moderate birefringence of 0.076@1064 nm. Additionally, C(NH2)3ClO4 has excellent ferroelectric properties and reversal of domains, which also enables it to produce ultraviolet coherent light as short as 200 nm by a quasi-phase matching technique with a periodically poling method. Our study may provide not only a promising UV NLO crystal but also a new π-conjugated functional unit, [C(NH2)3]+, which will open a path to finding new classes of high-performance UV NLO crystals.

Borosilicate Crystal LaBSiO5: A New Promising Ultraviolet Quasiphase Matching Material

AbstractNonlinear optical crystals with ferroelectricity, which could realize ultraviolet/deep‐ultraviolet coherent output by the quasiphase matching technology, are expected to be promising candidates for the new type of ultraviolet/deep‐ultraviolet nonlinear optical materials. Here, a new borosilicate crystal, LaBSiO5, is found, which is superior to the famous commercial quasiphase matching crystals, LiNbO3, KTiOPO4, and LaBGeO5 in performances. LaBSiO5 crystal exhibits excellent optical and electrical properties, including a short absorption cutoff (186 nm), a moderate second‐harmonic generation response (≈1.1 × KH2PO4), and the ferroelectric polarization reversal (coercive field ≈ 36.98 kV cm−1, remnant polarization ≈ 1.83 µC cm−2). Besides, no layering tendency is found during the process of crystal growth. Therefore, LaBSiO5 crystal is a potential ultraviolet quasiphase matching material.

Regulating Guanidinium-Based Hybrid Materials for Ultraviolet Nonlinear Optical Applications by Hybrid Strength and Hybrid Pattern.

Combining the advantages of organic and inorganic motifs, organic-inorganic hybrid materials can exhibit excellent nonlinear optical (NLO) performance. In this article, through systematic first-principles modeling and simulations, we investigated the NLO performance of an organic planar conjugated guanidinium cation [C(NH2)3+, guanidinium (GU)] and its hybrid materials with various inorganic anionic groups. It is demonstrated that GU-based hybrid materials are excellent candidates for ultraviolet (UV) NLO conversion, especially for the important 266 nm laser output in the solar-blind region, because of their wide UV transparency, strong second harmonic generation (SHG) effect, and large optical birefringence. Moreover, the UV NLO performance can be regulated by the hybrid strength and/or hybrid pattern between the GU cations and different kinds of inorganic anionic groups, which would help to explore new UV NLO materials in the hybrid material system.

Enhanced Ultraviolet Damage Resistance in Magnesium Doped Lithium Niobate Crystals through Zirconium Co-Doping.

MgO-doped LiNbO3 (LN:Mg) is famous for its high resistance to optical damage, but this phenomenon only occurs in visible and infrared regions, and its photorefraction is not decreased but enhanced in ultraviolet region. Here we investigated a series of ZrO2 co-doped LN:Mg (LN:Mg,Zr) regarding their ultraviolet photorefractive properties. The optical damage resistance experiment indicated that the resistance against ultraviolet damage of LN:Mg was significantly enhanced with increased ZrO2 doping concentration. Moreover, first-principles calculations manifested that the enhancement of ultraviolet damage resistance for LN:Mg,Zr was mainly determined by both the increased band gap and the reduced ultraviolet photorefractive center O2−/−. So, LN:Mg,Zr crystals would become an excellent candidate for ultraviolet nonlinear optical material.

Cover Feature: Sb6O7(SO4)2: A Promising Ultraviolet Nonlinear Optical Material with an Enhanced Second‐Harmonic‐Generation Response Activated by SbIII Lone‐Pair Stereoactivity (Chem. Eur. J. 19/2021)

Cover Feature: Sb₆O₇(SO₄)₂: A Promising Ultraviolet Nonlinear Optical Material with an Enhanced Second‐Harmonic‐Generation Response Activated by Sb^III Lone‐Pair Stereoactivity (Chem. Eur. J. 19/2021)

Sb6 O7 (SO4 )2 : A Promising Ultraviolet Nonlinear Optical Material with an Enhanced Second-Harmonic-Generation Response Activated by SbIII Lone-Pair Stereoactivity.

The stereochemical activity of lone pairs (SCALP) in a cation favors the formation of acentric materials and can enhance the second-harmonic-generation (SHG) response and/or the birefringence. By introducing functional SbIII into sulfates, an anhydrous sulfate of Sb6 O7 (SO4 )2 (1) is explored. Sb3+ cations are in seesaw configurations and in-phase aligned in a 3D asymmetric dense structure. Compound 1 exhibits an enhanced phase-matching SHG response, a moderate birefringence, a wide transparency window, and considerable environmental stabilities, which result in it being a promising UV nonlinear optical (NLO) material. Theoretical studies reveal that the stereoactive lone pairs on Sb3+ cations make the predominant contribution to the SHG effect. This work will attract more interest from scientists for research into SCALP-cation-based NLO materials.

From silicates to oxonitridosilicates: improving optical anisotropy for phase-matching as ultraviolet nonlinear optical materials.

Oxonitridosilicates, in which O atoms in SiO4 are partially substituted by N atoms, are proposed to improve optical anisotropies of silicates as UV NLO materials. The optical properties calculation showed that the heteroleptic SiOxN4-x (x = 1-3) tetrahedra have strong polarizability anisotropy and large hyperpolarizability. Accordingly, nine noncentrosymmetric (NCS) oxonitridosilicate crystals collected in the inorganic crystal structural database (ICSD) are evaluated by using the first principles method. Finally, Si2N2O and LiSiON are screened out owing to wide band gaps (6.49 and 6.95 eV), large birefringences (0.102 and 0.060 at 1064 nm), and large SHG coefficients (3.3 and 2.2 times that of d36(KDP)). More importantly, the cation selection and structural characteristics that are beneficial for enhancing the band gap and birefringence are identified. This study provides a novel strategy to design and find UV NLO crystals.