UV Cutoff Edge Research Articles

Shedding Light on the Structure and Characterization of K2ZnGe2O6: A Phase-Matchable Nonlinear Optical Crystal.

Nonlinear optical (NLO) materials have recently aroused great interest owing to their capability of frequency conversion in solid-state lasers. Herein, we report an acentric zinc germanate K2ZnGe2O6 obtained successfully through spontaneous crystallization methods. It affords a novel three-dimensional (3D) framework comprised of [GeO4] and [ZnO4] motifs with K atoms located in the tunnels. K2ZnGe2O6 displays a moderate second-harmonic-generation (SHG) intensity (0.73 × KDP) with phase-matchable behavior. Optical characterization demonstrated that it has a UV cutoff edge located at 368 nm with a large energy band of 3.23 eV, accompanied by a wide transmission window, covering a 3-5 μm atmospheric window. Moreover, thermal properties implied that it possesses intriguing thermal stability of 987 °C and a congruent melting nature. Additionally, first-principles calculations unveiled that the NLO performance was primarily attributed to the collective effect of [GeO4] and [ZnO4] building units. These findings indicate that K2ZnGe2O6 is a potential NLO crystal.

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd).

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d10 electron configuration, and 6s2 lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB4 O6 F2 (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, MII B4 O6 F2 (MII =Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB4 O6 F2 structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB4 O6 F2 structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.

Li3[Al(PO4)2(H2O)1.5] and Na[AlP2O7]: from 2D layered polar to 3D centrosymmetric framework structures

Two new aluminophosphates with moderate NLO property or a short UV cut-off edge (∼190 nm) are reported.

Large optical anisotropy-oriented construction of a carbonate-nitrate chloride compound as a potential ultraviolet birefringent material.

The design of new birefringent materials is very significant owing to their indispensable role in modulating the polarization of light and is vital in laser technology. Herein, by applying a large optical anisotropy-oriented construction induced by a synergy effect of multiple anionic groups, a promising carbonate-nitrate chloride, Na3Rb6(CO3)3(NO3)2Cl·(H2O)6, has been designed and synthesized successfully by the solvent evaporation method and single crystals of centimeter size were obtained by the recrystallization method in aqueous solution. It crystallizes in the hexagonal P63/mcm space group, the RbO9Cl polyhedra and the NaO7 polyhedra construct a three-dimensional (3D) framework by sharing O or Cl atoms and trigonal plane units (CO3 and NO3). The transmittance spectrum based on a 1 mm thick single-crystal plate shows that its short UV cut-off edge is about 231 nm. And the refractive index differences (0.14 @ 546 nm) measured by using a polarizing microscope on the (101) crystal plane, proves that Na3Rb6(CO3)3(NO3)2Cl·(H2O)6 has a large birefringence, which has potential application in the solar blind ultraviolet region. The theoretical calculations reveal that the π-conjugated CO3 and NO3 groups are the main cause of the birefringence. It demonstrates that combining π-conjugated CO3 and NO3 groups in one structure is an extremely effective strategy to explore new UV birefringent crystals.

Sr3B14O24: a new borate with a [B14O30] fundamental building block and an unwonted 2D double layer.

A new alkaline-earth metal borate, Sr3B14O24, was successfully synthesized by a high-temperature solution method. It crystallizes in the monoclinic space group P21/c (no. 14) and features a fundamental building block (FBB) [B14O30] which is composed of eight [BO3] and six [BO4] units. The FBBs further condense to form an unwonted infinite 2D double layer extended in the bc plane. The UV-Vis-NIR diffuse reflectance spectrum shows that the cutoff edge of Sr3B14O24 is less than 200 nm, which indicates its potential use in the deep UV region. In addition, the first principles theoretical study was carried out to better understand the relationship between the structure and performance.

CsB3O4(OH)2: a new deep-ultraviolet birefringent crystal with [B3O4(OH)2] anionic group.

A new cesium hydroxyborate CsB3O4(OH)2, was designed and synthesized by a hydrothermal method. Remarkably, CsB3O4(OH)2 presents novel [B3O4(OH)2]∞ chains formed by [B3O4(OH)2] fundamental building blocks (FBBs). The report of less common [B3O4(OH)2] FBBs and [B3O4(OH)2]∞ chains in CsB3O4(OH)2 enriches the structural diversity of hydroxyborates. In addition, CsB3O4(OH)2 has a wide transparent window in the DUV spectral range and a large birefringence.

Cs2VOF4(IO2F2): Rationally designing a noncentrosymmetric early-transition-metal fluoroiodate

Cs2VOF4(IO2F2) exhibits a strong SHG response (5 × KH2PO4(KDP) at 1064 nm), a moderate birefringence (0.088@1064 nm), and a short UV cutoff edge (257 nm).

C(NH2)3]2S2O8: combining delocalized and localized π-conjugate units to achieve strong optical anisotropy

The optimizing combination of organic delocalized π-conjugated units and inorganic structural units with localized π orbitals leads to large birefringence and short UV cut-off edge.

Na3YB8O15: a new rare-earth borate with an infinite one-dimensional [B8O15]∞ chain and a short ultraviolet cutoff edge.

A new rare-earth borate Na3YB8O15 was fabricated by the flux method. The compound crystallizes in the P1̄ group, and shows a three-dimensional network built by [B8O17] fundamental building blocks (FBBs) with [NaO6], [NaO7], and [YO7] polyhedra. The [B8O17] FBBs are composed of five planar BO3 and three BO4 tetrahedra and connected via corner-sharing to construct a unique one-dimensional (1D) [B8O15]∞ infinity chain that is observed for the first time in the Na2O-Y2O3-B2O3 system compound, enriching the structural diversity of rare-earth borate. The title compound exhibits a short ultraviolet (UV) cutoff edge of ∼195 nm and a wide experimental band gap of 5.50 eV. DFT calculations indicate that Na3YB8O15 is a direct band gap compound with a calculated GGA band gap of 5.14 eV, and the band gap is mainly determined by B 2p and O 2p orbitals. The results update the phase diagram of Na2O-Y2O3-B2O3 and enrich the diversity of rare-earth metal borates.

Flux Growth and Properties of Volatile Bromine-Containing UV Nonlinear Optical Crystal K3B6O10Br

A UV Nonlinear optical (NLO) crystal is one of the key devices in all-solid-state laser technology, and borate halides show outstanding potential due to their abundant structural diversity and short UV cut-off edges. In this article, the sizable UV NLO crystal of K3B6O10Br (KBOB) has been grown with lead-containing and lead-free fluxes systems using the high-temperature top-seeded solution growth (TSSG) method. Energy Dispersive X-ray Spectroscopy (EDS) and transmittance spectra illustrate the influence of Pb2+ ions on the transmittance properties and laser-induced damage threshold (LDT). The thermal property, namely, thermal expansion, thermal conductivity, and thermal diffusivity curves, were characterized. Moreover, a small variation of thermal refractive indexes was analyzed to illustrate the advantage of KBOB in the application for temperature-fluctuated specific regions.

Investigations on the Synthesis, Crystal Structure, Linear- and Nonlinear-Optical Properties of the Zinc Germanate Rb2ZnGe2O6.

A quaternary nonlinear-optical (NLO) zinc germanate, Rb2ZnGe2O6 (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group C2221 (No. 20) and features a 3D framework formed by GeO4 tetrahedra, ZnO4 tetrahedra, and Rb+ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH2PO4. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.

Na+/Ag+ substitution induced birefringence enhancement from AgGaS2 to NaGaS2

Birefringent materials are of great important as opto-electronic functional devices in solid laser system. Investigations on the design of new birefringent materials with large birefringence is meaningful. In this study, structure-birefringence relationship between AgGaS2 (AGS) and NaGaS2 (NGS) was systematically investigated. In the structures, the high ionic Na+ cations broke the three dimensional (3D) [GaS] network to 2D layers, which results in the regular packing of GaS4 tetrahedra and further the birefringence (~0.09, nearly twice that of AGS at ~1064 nm). Meanwhile, the blue-shift of the UV cutoff edge to 307 nm and a wide band gap of 3.9 eV has been observed in NGS. The property characterizations were carried out using the as-grown NGS single crystal with a size of 4 × 4 × 0.3 mm3 by high temperature flux method. The results indicate that NGS may be a promising IR birefringent material and the cation substitution-oriented design strategy could be used to regulate the structure and optical properties of materials.

Achieving Short‐Wavelength Phase‐Matching Second Harmonic Generation in Boron‐Rich Borosulfate with Planar [BO3] Units

AbstractUltraviolet (UV) nonlinear optical (NLO) crystals which can produce short‐wavelength lasers via a direct second harmonic generation (SHG) process are of great importance in modern laser technology. Currently, the exploration of UV NLO crystals in borosulfates is nearly stagnant since the non‐phase matching (PM) property lies on the small birefringence induced by the intrinsically small optical anisotropy of the tetrahedral groups. Herein, for the first time, the planar [BO3] units were introduced into borosulfates leading to a boron‐rich borosulfate (NH4)2B4SO10 with unprecedented [B4SO10]∞ layers and evidently enhanced birefringence. To the best of our knowledge, it achieves the shortest SHG PM wavelength of 252 nm in all reported borosulfates with deep UV cutoff edge (184 nm), large SHG response (1.1×KDP at 1064 nm and 0.15×β‐BBO at 532 nm) and large birefringence (0.053 at 1064 nm) and is easy to grow single crystals via simple chemical vapor deposition method. These results confirm the feasibility of utilizing planar [BO3] units to optimize birefringence of borosulfates, and also open up broad prospects for UV NLO crystals in boron‐rich borosulfates.

Achieving Short-Wavelength Phase-Matching Second Harmonic Generation in Boron-Rich Borosulfate with Planar [BO3 ] Units.

Ultraviolet (UV) nonlinear optical (NLO) crystals which can produce short-wavelength lasers via a direct second harmonic generation (SHG) process are of great importance in modern laser technology. Currently, the exploration of UV NLO crystals in borosulfates is nearly stagnant since the non-phase matching (PM) property lies on the small birefringence induced by the intrinsically small optical anisotropy of the tetrahedral groups. Herein, for the first time, the planar [BO3 ] units were introduced into borosulfates leading to a boron-rich borosulfate (NH4 )2 B4 SO10 with unprecedented [B4 SO10 ]∞ layers and evidently enhanced birefringence. To the best of our knowledge, it achieves the shortest SHG PM wavelength of 252 nm in all reported borosulfates with deep UV cutoff edge (184 nm), large SHG response (1.1×KDP at 1064 nm and 0.15×β-BBO at 532 nm) and large birefringence (0.053 at 1064 nm) and is easy to grow single crystals via simple chemical vapor deposition method. These results confirm the feasibility of utilizing planar [BO3 ] units to optimize birefringence of borosulfates, and also open up broad prospects for UV NLO crystals in boron-rich borosulfates.

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.

The First Mixed Calcium Zinc Borate with a Flexible [B8O17] Fundamental Building Block and Short UV Cutoff Edge

The first mixed calcium zinc borate with a new fundamental building block (FBB) [B8 O17 ], Ca1.13 Zn0.87 B8 O14 has been successfully synthesized. It exhibits two independent interpenetrating three-dimensional B-O anion networks constructed by [B8 O17 ] groups, enriching the structural diversity of B-O configurations. In particular, the UV-Vis-NIR diffuse-reflectance spectrum shows that it has a short UV cutoff edge (<195 nm).

Exploring Deep-UV Nonlinear Optical Materials with Enhanced Second Harmonic Generation Response and Birefringence in Fluoroaluminoborate Crystals.

Deep-UV (DUV) nonlinear optical (NLO) materials are of vital importance to demanding DUV laser applications; however, those with a large NLO coefficient, wide band gap, and sufficient phase-matching ability are rare. In this work, by combining π-conjugated B3O6 groups and distort AlO3F tetrahedra, we successfully designed and synthesized two fluoroaluminoborates, RbAlB3O6F (RABF) and Cs0.5Rb0.5AlB3O6F (CRABF). In addition, the solid solution CsxRb1-xAlB3O6F (0.2 < x < 0.8) polycrystalline samples were obtained by the standard solid-state reaction. It was shown that all these compounds are NLO-active and possess short UV cutoff edges (<200 nm). Interestingly, although they have the same fundamental structural units, their crystal structures and second harmonic generation (SHG) responses are significantly different owing to the cation effect. Theoretical calculations reveal that both B3O6 and AlO3F groups contribute to the SHG responses. Remarkably, it also indicates that RABF exhibits a large birefringence (Δn = 0.0946 at 1064 nm), which is capable of realizing deep-UV phase matching down to 174 nm. The exploration of fluoroaluminoborates provides a new perspective for searching excellent deep-UV NLO materials.

A 3D supramolecular framework assembled via π⋅⋅⋅π interactions and CH⋅⋅⋅Cl hydrogen-bonds with second-harmonic generation response

A three-dimensional (3D) supramolecular framework [CuII2Cl3(tpen)]2⋅[CuIICl4] (1) (tpen = N,N,N',N'-tetra(2-pyridylmethyl) ethylenediamine) assembled from [CuII2Cl3(tpen)]+ and [CuIICl4]2– via π⋅⋅⋅π interactions and CH⋅⋅⋅Cl hydrogen-bonds has been obtained by solvothermal synthesis. The π-stacked supramolecular layers of the [CuII2Cl3(tpen)]+ ions are connected by the [CuIICl4]2– anions in a distorted tetrahedral geometry to form a 3D architecture via CH⋅⋅⋅Cl hydrogen-bonds. Due to the helical alignment of the [CuII2Cl3(tpen)]+ and the oriented [CuIICl4]2–, compound 1 crystallizes in the tetragonal non-centrosymmetric (NCS) space group P–421/c. The compound shows a moderate band-gap of 2.48 eV and a UV cutoff edge of 420 nm. For the NCS structure of compound 1, a phase-matchable second harmonic generation (SHG) response of ~0.009 times that of KH2PO4 (KDP) was observed.

Two deep-ultraviolet nonlinear optical barium borates framework: Alkali metal enhances the second-harmonic generation response

Two non-centrosymmetric barium borates with acs-type net, namely Ba3 [B9O16][B(OH)4]·2H2O (1) and NaBa3(OH)[B9O16][B(OH)4] (2) have been synthesized under hydrothermal conditions. Compound 1 is type-I phase matchable with second-harmonic generation (SHG) response of approximately 1.6 times than that of KDP (KH2PO4). After Na+ cation has been successfully introduced into the oxoboron cluster backbone, compound 2 displays a larger SHG response about approximately 2.0 times of KDP. The calculations show that the large local dipole moments of distorted NaO7 polyhedrons make 2 exhibits a relatively larger SHG response. The ultraviolet–visible (UV–Vis) diffuse reflectance spectra show that both 1 and 2 have a wide transparency range with UV cutoff edge below 200 ​nm. These properties reveal that the introduction of different size and charge alkali metal on the basis of alkaline earth metal borate is beneficial to obtain a promising deep-ultraviolet nonlinear optical (NLO) material with a larger SHG response.

Two Lead Halides with Strong SHG Response Obtained by the Isovalent Substitutions of Alkali Metal Cation and Halogen Anion.

The substitution of alkali metal cation or halogen anion based on nonlinear crystals is an effective strategy to exploit new optical materials. The strategy has been successfully expanded to discover two new lead halides, Rb3Pb2(CH3COO)2X5 (X = Br, Cl). The substitution of the Cs+ cation with a Rb+ cation can not only increase the local dipole moment of the distorted [PbBr4O2] polyhedron but also reduce the cell unit, resulting in a large net macroscopic polarization. Therefore, Rb3Pb2(CH3COO)2Br5 possesses a strong second-harmonic generation (SHG) response (6 × KDP) and a large birefringence (0.18@1064 nm). Furthermore, by the substitution of the Br- anion with a Cl- anion, Rb3Pb2(CH3COO)2Cl5 exhibits a high laser damage threshold (LDT, 84 × AgGaS2) and a short UV cutoff edge of 287 nm, as well as moderate SHG response (3 × KDP) and birefringence (0.11@1064 nm). Detailed theory calculations elucidate the origin of the linear and nonlinear optical properties of these compounds.