Large Birefringence Research Articles

Pb2(SeO3)(SiF6): the first selenite fluorosilicate with a wide bandgap and large birefringence achieved through perfluorinated group modification.

Birefringent crystals serve as the core elements of polarizing optical devices. However, the inherent challenge of balancing bandgap and birefringence poses a significant hurdle in designing crystals with excellent overall performance. In this study, we propose a novel approach, namely modification with perfluorinated groups, to achieve dual enhancement of the bandgap and birefringence of selenite materials. We have successfully synthesized the first selenite fluorosilicate, namely, Pb2(SeO3)(SiF6). This compound exhibits a three-dimensional structure composed of two-dimensional lead selenite layers bridged by SiF6 octahedrons. Notably, by introducing a perfluorinated SiF6 group, the bandgap of the lead selenite compound has been expanded to 4.4 eV. Furthermore, Pb2(SeO3)(SiF6) demonstrates a large birefringence (0.161 @ 546 nm), surpassing most of the selenite compounds with a bandgap larger than 4.2 eV. Theoretical calculations suggest that the large birefringence of Pb2(SeO3)(SiF6) can be attributed to the synergistic effects of SeO3, PbO4 and PbO3F4 polyhedrons. Our research not only pioneers a new system for selenite materials, enriching the diversity of selenite structures, but also provides a design methodology for obtaining wide bandgap birefringent selenite.

RbSr3X][(BS3)2] (X = Cl, Br): two salt-inclusion thioborates with large birefringence and structure transformation from centrosymmetric to asymmetric.

[RbSr3X][(BS3)2] (X = Cl, Br), two salt-inclusion chalcogenides with planar [BS3] as anionic units, were obtained. Structure analysis indicates that the size effect of halogens may adjust the arrangement between the [BS3] units and further lead to the CS-to-NCS structure transformation. Experimental characterizations reveal that they have wide bandgaps (3.64-3.70 eV), large birefringence (0.136-0.144) and high LIDT (12-14 × AgGaS2). This work indicates that the thioborate family is a rich source to explore structure chemistry and promising infrared functional materials.

Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O: two tin(II) fluoride oxalates display large birefringence.

Birefringent materials play an important role in laser techniques as an essential part of optical devices. Therefore, the exploration of high-performance birefringent materials has been a central focus of researchers. Herein, two tin(II) fluoride oxalates Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O were gained by the combination of birefringence-active groups of Sn2+ with stereochemically active lone pairs and planar π-conjugated [C2O4]2- groups. These groups assemble into low-dimensional structures of 0D [C2O4F4]6- clusters and 1D [SnC2O4F]∞- chains in Na4Sn4(C2O4)3F6, and double [Sn2(C2O4)2F2]∞2- chains in NaSnC2O4F·H2O, which gives rise to the large birefringence of 0.160@546 nm and 0.189@546 nm, respectively. Detailed structure-property analysis and theoretical calculations indicate that strong optical anisotropy can be induced by the rational arrangement of the Sn2+-polyhedra and [C2O4]2- groups.

Chemical modulation of AIREIIICIVQVI4 family compounds for band gap and optical anisotropy enhancement

By introducing [AgS3] and [NaQ6] (Q = S, Se) into the AIREIIICIVQVI4 family, four new RE-based chalcogenides with wide band gaps and large birefringence have been rationally designed and fabricated.

Chromium iodate: the structure and origin of optical second harmonic generation.

Iodate crystal materials are some of the important candidates for mid-infrared nonlinear optical (NLO) crystals. Almost all the structures and NLO properties of monometallic iodates have been studied, except for a few difficult to synthesize crystalline phases. In this work, crystalline Cr(IO3)3 was synthesized and its optical properties were studied. Cr(IO3)3 has a strong powder second-harmonic generation (SHG) effect (1.3 × AgGaS2) and a large birefringence (0.24) at 2100 nm. Theoretical calculations indicate that the 3d orbital of Cr3+ is strongly involved in the SHG process, and the contribution of the metal cation centered unit CrO6 to the SHG response is much greater than that of the non-metal cation centered unit IO3. This study provides a new case among the few NLO materials in which the SHG response is dominated by metal cation centered groups.

PbTeB4O9: a lead tellurium borate with unprecedented fundamental building block [B4O10] and large birefringence.

Herein, the first lead tellurium borate, PbTeB4O9, with an unprecedented fundamental building block [B4O10] was successfully synthesized. The near-parallel alignment of [B4O10] groups and [TeO3] polyhedra resulted in a high birefringence (0.099@1064 nm). The structure-property relationship was discussed by using the first-principles calculations.

HgBr2: an easily growing wide-spectrum birefringent crystal.

Birefringent materials are of great significance to the development of modern optical technology; however, research on halide birefringent crystals with a wide transparent range remains limited. In this work, mercuric bromide (HgBr2) has been investigated for the first time as a promising birefringent material with a wide transparent window spanning from ultraviolet (UV) to far-infrared (far-IR) spectral regions (0.34-22.9 μm). HgBr2 has an exceptionally large birefringence (Δn, 0.235 @ 546 nm), which is 19.6 times that of commercial MgF2. The ordered linear motif [Br-Hg-Br] with high polarizability anisotropy within the molecule is the inherent source of excellent birefringence, making it an efficient building block for birefringent materials. In addition, HgBr2 can be easily grown under mild conditions and remain stable in air for prolonged periods. Studying the birefringent properties of HgBr2 crystals would provide new ideas for future exploration of wide-spectrum birefringent materials.

Design of alkali lead oxybromides with strong second-harmonic generation response and large birefringence

Design of alkali lead oxybromides with strong second-harmonic generation response and large birefringence

1D Cu(I)-based chiral organic-inorganic hybrid material with second harmonic generation and circular polarized luminescence.

In recent years, organic-inorganic hybrid materials have demonstrated exceptional performance in nonlinear optics, attracting widespread attention. However, there are relatively few examples of coordination compounds synthesized with Cu as the metal center that exhibit excellent nonlinear optical properties. In this study, we successfully synthesized a pair of enantiomers named R/S-Cu2I2 by reacting chiral ligands with CuI. The crystal structure reveals a one-dimensional copper-iodide chain structure built by Cu2I2 clusters, and its ordered arrangement in space provides not only a strong second harmonic generation (SHG) signal (1.24 × KDP) but also a large birefringence (0.15@1064 nm). Under excitation at 395 nm, the crystals exhibit red fluorescence peaked at 675 nm. The CD spectra of R/S-Cu2I2 show a distinct mirror-symmetric Cotton effect, and their CPL signals are corresponding and opposite in the emission range, with a maximum glum of approximately ±2.5 × 10-3. Theoretical calculations using density functional theory were also carried out to enhance our understanding of the correlation between their structures and optical properties.

From NaGa(IO3)3F to NaGa(IO3)2F2 and NaGa(IO3)4: The Effects of Chemical Substitution between F- Anions and IO3- Groups on the Structures and Properties of Gallium Iodates.

Introducing F- anions or substituting F- anions with IO3- groups has been proven to be ideal strategies for designing novel noncentrosymmetric (NCS) and polar materials, yet systematic investigation into the effect of F- anions or the substitution of IO3- for F- anions on structures and properties remains rarely explored. Herein, two new gallium iodates, NaGa(IO3)2F2 (1) and NaGa(IO3)4 (2), were successfully designed and synthesized based on NaGa(IO3)3F by introducing more F- anions and replacing F- anions with IO3 groups, respectively. Structurally, in compound 1, the adjacent [GaF3(IO3)3]3- polyanions are connected in an antiparallel manner, resulting in a complete cancellation of local polarity. While in compound 2, all IO3 groups in 2D [Ga(IO3)4]∞- layers are aligned, leading to large macroscopic polarization. Additionally, chemical substitution also results in a qualitative improvement in the functional properties of compound 2. It possesses strong SHG response (12 × KDP @1064 nm) and broad optical transparency, coupled with large birefringence (0.21 @1064 nm), showcasing its promise as a promising nonlinear optical (NLO) crystal. The effects of chemical substitution between F- anions and IO3- groups on the structures and properties are discussed in detail.

Computer-aided screening of bismuth molybdates nonlinear optical crystals γ-Bi2MoO6

γ-Bi2MoO6 exhibits a 9.9-times stronger second harmonic generation (SHG) response than that of KDP, large birefringence of 0.21 at 1064 nm, and relatively large band gap of 2.57 eV.

K2MgMoP2O10 and K3Mg2MoP3O14: two new molybdophosphates exhibiting different optical anisotropies induced by variable dimensionality of the anion framework.

By introducing the d0 metal cation Mo6+ into phosphates, two new molybdophosphates, K2MgMoP2O10 and K3Mg2MoP3O14, were synthesized by spontaneous crystallization, and their structures were determined by single-crystal X-ray diffraction. K2MgMoP2O10 shows a two-dimensional layer composed of the uncommon eight-membered ring [Mo2P2O16] formed by [MoO6] and [PO4], while K3Mg2MoP3O14 shows isolated [MoP3O14] clusters composed of [MoO5] and [PO4]. K2MgMoP2O10 and K3Mg2MoP3O14 have UV cut-off wavelengths of 277 and 271 nm, respectively, which are significantly shorter than those of most recently published molybdophosphates. To the best of our acknowledge, K2MgMoP2O10 exhibits the largest birefringence (a calculated value of 0.187 at 546 nm) among reported alkali metal or alkaline earth metal molybdophosphates, which provides a way to explore new birefringent materials. First-principles analysis of the electronic structure shows that the large birefringence of K2MgMoP2O10 mainly originates from the [MoO6] units.

Large optical anisotropy in noncentrosymmetric phosphate with pseudo 2D intercalated layer

A noncentrosymmetric phosphate (C3H5N2)(H2PO4) with pseudo 2D intercalated layers, which exhibits large birefringence and wide band gap, was successfully synthesized by simultaneously introducing the planar and tetrahedral motifs.

(C5H6N2)2H](Sb4F13): a polyfluoroantimonite with a strong second harmonic generation effect.

It is of great difficulty to create a new antimonite with second-harmonic-generation (SHG) intensity larger than 6 times that of KDP. In this study, a polyfluoroantimonite strategy has been proposed to explore fluoroantimonites with large nonlinear optical (NLO) coefficients. Under the cooperation of chemical (highly asymmetric π-conjugated organic amine) and physical (viscous reaction medium ethylene glycol) methods, two novel polyfluoroantimonites, namely, (3PC)2(Sb4F14) and (3AP)2(Sb4F13), have been achieved. Interestingly, these two structures contain two new polyfluoroantimonite groups respectively, an isolated (Sb4F14)2- four-member polyhedral ring and an infinite [Sb4F13]∞- helical chain. More importantly, the polar (3AP)2(Sb4F13) displays a strong SHG intensity of 8.1 × KDP, a large birefringence of 0.258@546 nm and a high laser-induced damage threshold (LIDT) value of 149.7 MW cm-2. Theoretical calculations indicated that its strong SHG effect stems from the synergistic effect of the helical [Sb4F13]∞- polyfluoroantimonite chain and π-conjugated 3AP+ cation, with a contribution ratio of 48.93% and 50.77% respectively. This work provides a new approach for the design and synthesis of high-performance fluoroantimonites.

KBa3M2F14Cl (M = Zr, Hf): novel short-wavelength mixed metal halides with the largest second-harmonic generation responses contributed by mixed functional moieties

First phase-matchable metal mixed halides with deep-ultraviolet transmittance, KBa3M2F14Cl (M = Zr, Hf), show largest SHG effects coming from isolated MF7 units, Ba2+ and Cl− cations. And the optimally aligning MF7 units work for large birefringence.

Discovery of a new bimetallic borate with strong optical anisotropy activated by π-conjugated [B2O5] units.

Birefringent materials with high optical anisotropy have been identified as a research hotspot owing to their significant scientific and technological significance in modern optoelectronics for manipulating light polarization. Researchers studying borate systems have discovered that adding π-conjugated units placed in parallel can significantly increase the birefringence of crystalline solids; some examples include [BO3] units, [B2O5] units, and [B3O6] units. However, there are not many borates with strictly parallel configurations of π-conjugated [B2O5] units. In this study, a new bimetallic borate Sr2Cd4(B2O5)3 with near-parallel arrangement of π-conjugated [B2O5] units was discovered. Sr2Cd4(B2O5)3 possesses the maximum number density of [B2O5] units, shortest dihedral angle of [B2O5] units (between the two [BO3]), and largest degree of [CdO6] octahedral distortion among all the currently known Sr-Cd-B-O tetragonal system borates, making it demonstrate a large birefringence of 0.102 at 532 nm. Theoretical analysis proves that π-conjugated [B2O5] anions are the primary source of the large birefringence of Sr2Cd4(B2O5)3.

Ag2[TeO2(OH)4]: a nonlinear optical tellurate with balanced comprehensive performance

A single crystal of Ag2[TeO2(OH)4] with size of 8 × 4 × 4 mm3 was obtained, which exhibits balanced comprehensive performances, including a large second-harmonic generation response of 0.84 × AgGaS2 and large birefringence of 0.106@1064 nm.

Crystal clear: unveiling giant birefringence in organic-inorganic cocrystals.

Coplanar groups with large anisotropic polarizability are suitable as birefringence-active groups for investigating compounds with significant birefringence. In this study, the organic coplanar raw reagent, o-C5H5NO (4HP), was selected as an individual complement. Utilizing the cocrystal engineering strategy, we successfully designed two cocrystals: [LiNO3·H2O·4HP]·4HP (Li-4HP2) and [Mg(NO3)2·6H2O]·(4HP)2 (Mg-4HP), and one by-product: LiNO3·H2O·4HP (Li-4HP), which were grown using a mild aqua-solution method. The synergy of the coplanar groups of NO3 - and 4HP in the structures resulted in unexpectedly large birefringence values of 0.376-0.522@546 nm. Furthermore, the compounds exhibit large bandgaps (4.08-4.51 eV), short UV cutoff edges (275-278 nm), and favorable growth habits, suggesting their potential as short-wave UV birefringent materials.

“Three‐in‐One”: A New Hg‐Based Selenide Hg7P2Se12 Exhibiting Wide Infrared Transparency Range and Strong Nonlinear Optical Effect

AbstractThe exploration of high‐performance mid‐ and far‐infrared (IR) nonlinear optical (NLO) crystals is an urgent need. Herein, a new Hg‐based selenide Hg7P2Se12 (HPSe) is designed and synthesized by a rigid and flexible units coupled strategy. It is interesting that in the compound, three types of NLO‐active units, including linear [HgSe2], triangular [HgSe3], and tetrahedral (MSe4) (M = Hg/P) groups, simultaneously exist. It shows a wide transparency range (0.84–22.8 µm), large SHG response (1 × AGS), high laser‐induced damage threshold (≈2 × AGS), and a large birefringence (0.102 @ 2090 nm). Moreover, the compound melts congruently along with good crystal growth habits, and single crystals with a maximum size of ≈7 × 5 × 2 mm3 are obtained. Theoretical analyses confirm that the large NLO response originates from the synergistic effects of Hg–Se units, (PSe4) and nonbonding electrons. The results indicate that HPSe is a promising mid‐ and far‐IR NLO material, and inspire a path to finding new classes of IR NLO materials that are different from traditional chalcopyrite materials by grouping the linear, planar, and tetrahedral units.

(C(NH2)3)2(I2O5F)(IO3)(H2O) and C(NH2)3IO2F2: Two Guanidine Fluorooxoiodates with Wide Band Gap and Large Birefringence.

Enhancing anisotropy through an effective synergistic arrangement of anionic and cationic groups is crucial for improving the birefringence optical properties of materials. In this work, by transforming I-O into I-F through the fluorination strategy, two metal-free guanidine fluorooxoiodates (C(NH2)3)2(I2O5F)(IO3)(H2O) and C(NH2)3IO2F2 and one guanidine iodate C(NH2)3IO3 were successfully synthesized using the hydrothermal method. An unprecedented dimer [I2O5F] formed by [IO3F] and [IO3] in (C(NH2)3)2(I2O5F)(IO3)(H2O) was found, which greatly enriches the structural diversity of fluorooxoiodates. All three compounds feature a relatively large birefringence (Δn = 0.068, 0.110 and 0.075 at 546 nm) and a short ultraviolet cutoff edge. The theoretical calculation was carried out to understand the electronic structures and linear optical properties.