Large Birefringence Research Articles

Li3B8O13X (X = Cl and Br): Two New Noncentrosymmetric Crystals with Large Birefringence Induced by BO3 Units

Enthusiasm for the exploration of nonlinear alkali metal borates remains high. Focusing on the Li-B-O-X (X = Cl and Br) system, two examples of noncentrosymmetric borates, Li3B8O13Cl and Li3B8O13Br, were obtained using a high-temperature solution method under vacuum conditions. Structurally, the Li3B8O13X crystals exhibit two independent alternately arranged three-dimensional B-O network structures formed by the basic building block unit B8O16. The performance measurements demonstrate their short ultraviolet cutoff edges. The theoretical calculation indicates that the BO3 units dominate the contribution to their large optical anisotropy with the birefringence, 0.094 and 0.088@1064 nm for Li3B8O13Cl and Li3B8O13Br, respectively.

CsHfF4(IO3): A Hafnium Iodate Exhibiting a Strong Second-Harmonic-Generation Effect and a Wide Band Gap Achieved by Mixed-Ligand Acentric Coordination.

A new polar hafnium iodate, CsHfF4(IO3), was successfully designed and synthesized by integrating fluorinated hafnium-oxygen polyhedra (HfF6O2) and IO3- anionic functional groups. Owing to the weak electronic effect of Hf4+ and the bond-network-induced out-of-center distortion of the HfF6O2 dodecahedra, CsHfF4(IO3) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KH2PO4) and a rather large band gap (4.47 eV), which is the largest among the d0 transition-metal iodates. In addition, CsHfF4(IO3) possesses a wide transparent region (0.27-9.9 μm), a large birefringence for phase-matching (0.161), and a high laser-induced damage threshold (55.41 MW cm-2, 26 × AgGaS2) and is nonhygroscopic. This work indicates that the integration of mixed-ligand acentric coordination polyhedra and functional groups containing lone electron pairs is an effective strategy for developing novel inorganic nonlinear-optical materials with balanced overall properties.

α-BBO-like π-Conjugated Crystal with Large Birefringence

Birefringent crystals are in great demand for high performance polarizing devices. Designing new birefringent crystals with large birefringence remains a challenge. Herein, we successfully synthesized a new α-BBO-like π-conjugated birefringent crystal, K2HC3N3S3·1.5H2O (I). I exhibits a relatively large birefringence of 0.31@550 nm; such a birefringence is larger than those of most present commercial birefringent crystals. This result indicates that I might be a potential candidate for polarization modulation components in optical devices. First-principles calculations reveal that the planar π-conjugated [HC3N3S3]2– anions make dominant contributions in the large birefringence of I.

A Rare-Earth Selenite with Unexpectedly Well-Balanced Ultraviolet Nonlinear Optical Functionality, Sc(HSeO3 )3.

Establishing high performance ultraviolet (UV) nonlinear optical (NLO) selenite crystals with well-balanced properties is very challenging attributable to their strong absorption for UV light. Here a rare-earth selenite, Sc(HSeO3 )3 , with excellent UV NLO propertiesis introduced. Sc(HSeO3 )3 crystallizing in the polar NCS space group, Cc, features a 3D archetiture built up by interconnected ScO6 octahedra and HSeO3 groups. The crystal exhibits remarkably well-balanced UV-NLO functionality, namely, the shortest absorption edge (214nm) among NLO-active selenites, wide bandgap (5.28eV), large phase-matchable SHG response (5 × KDP), and sufficiently large birefringence (cal. 0.105 @1064nm). Detailed DFT calculations have been performed to elucidate the structure-property relationships. This work provides a new example of discovering novel UV NLO selenite materials.

Strong anisotropic optical response in two-dimensional Mo-VIA and Mo-VIIA monolayer binary materials

Two-dimensional binary materials based on transition metals have attracted much research attention because of their intriguing physical properties owing to their crystalline structure. The optical response of these compounds paves a way to manipulate the optical and electronic properties for optical and electronic device applications. Here, the frequency-dependent anisotropic linear optical response of eight molybdenum (Mo)-based binary materials from the VIA (i.e., O, S, Se, and Te) and VIIA (i.e., F, Cl, Br, and I) groups are systematically investigated using first-principles density functional theory. These binary materials exhibit strong linear anisotropic dielectric and optical behavior in the low energy range and become isotropic at high energies. The linear anisotropy in optical functions can be attributed to the intralayer excitonic behavior. The phenomenon of birefringence is the main characteristic of anisotropic materials. The dichroic ratio determines the degree of anisotropy. Among these binary materials, MoS2 and MoCl2 show large birefringence in the visible and far-infrared regions. The birefringence in these materials is also compared with other reported materials. Birefringence is critical for light manipulation during propagation through media. The present results provide insight into the linear optical anisotropies of the binary materials considered. Furthermore, the results suggest that these Mo-based binary materials could be potential candidates for developing optical instruments, optoelectronic, and photonic device applications.

Two Carboxylate-Cyanurates with Strong Optical Anisotropy and Large Band Gaps.

The first metal carboxylate-cyanurates, namely, K(H3C3N3O3)(HCO2) (I) and Ba2(H2C3N3O3)(CH3CO2)3(H2O) (II), which contain π-conjugated carboxylate and cyanurate groups, have been synthesized by hydrothermal methods. They crystallize in centrosymmetric space groups of P1̅ and P21/n, respectively. Compound I exhibits a novel three-dimensional (3D) structure based on a [K(H3C3N3O3)]+ cationic framework with 12-membered ring (12-MR) channels, and the (HCO2)- anions are located within the 12-MR channels. The [K(H3C3N3O3)]+ cationic framework is composed of K+ ions interconnected by H3C3N3O3 ligands. Compound II features a 3D network formed by [Ba2(CH3CO2)3]+ cationic double chains bridged by (H2C3N3O3)- anions. The [Ba2(CH3CO2)3]+ cationic double chain is composed of (CH3CO2)- anions and Ba2+ ions. Optical property measurements show that both compounds exhibit short ultraviolet cutoff edges (I, 208 nm; II, 218 nm) and wide band gaps (I, 5.43 eV; II, 5.20 eV). Importantly, K(H3C3N3O3)(HCO2) (I) features a large birefringence of 0.285@532 nm due to the parallel alignment of π-conjugated H3C3N3O3 and (HCO2)- groups, indicating that K(H3C3N3O3)(HCO2) (I) is a promising short-wave ultraviolet birefringent material. Detailed theoretical calculations elucidate that their excellent optical properties originate from the synergetic effect of both types of π-conjugated groups.

Growth and Optical Properties of Large-Sized NaVO2(IO3)2(H2O) Crystals for Second-Harmonic Generation Applications

Large-sized crystals of the quaternary iodate NaVO2(IO3)2(H2O) (NVIO) with centimeter-scale dimensions (23 mm × 18 mm × 6 mm as a representative) have been successfully grown by the top-seeded hydrothermal method. Linear optical properties have been measured, including the optical transmission spectrum and refractive index. The NVIO crystal possesses an optical window with high transmittance (above 80%) over the range of 500-1410 nm and exhibits strong optical anisotropy with large birefringence Δn (nz - nx) of 0.1522 at 1064 nm and 0.1720 at 532 nm. Based on the measured refractive indices, the phase-matching conditions for second-harmonic generation (SHG) have been calculated, and SHG devices have further been fabricated along the calculated type I and type II phase-matching directions of (θ = 39.0°, φ = 3.8°) and (θ =53.8°, φ = 1.3°). Laser experiments of extra-cavity frequency doubling have been performed on these NVIO devices. It has been confirmed that the effective SHG conversion from 1064 to 532 nm could be achieved with an energy conversion efficiency of 8.1%. Our work demonstrates that large-sized NVIO crystals are promising in the frequency-doubling application.

Na7(SeO4)3(IO3) and K2(SeO4)[IO2(OH)]: two new iodate-selenates with short-wave UV cutoff edge and large birefringence

By combining non-π-conjugated [SeO4] tetrahedra with highly polar [IO3]/[IO2(OH)] groups, large optical band gaps and large birefringence in two novel iodate-selenates Na7(SeO4)3(IO3) and K2(SeO4)[IO2(OH)] have been successfully achieved.

C3N6H7SO3NH2: non-π-conjugated tetrahedra decoupling π-conjugated groups achieving large optical anisotropy and wide band gap

A new melamine sulfamate crystal with large birefringence and wide band gap was synthesized by combining π-conjugated group and non-π-conjugated group.

Honeycomb layered topology construction for exceptional long-wave infrared nonlinear optical crystals.

Nonlinear optical (NLO) crystals capable of efficient long-wave infrared (8-14 μm) laser output remain scarce, and the exploration of long-wave IR NLO materials with superior comprehensive optical performances is a momentous challenge. Herein, we develop two selenide-halide NLO crystals, Hg3AsSe4Br and Hg3AsSe4I, which are derived from the honeycomb layered topology of prototype GaSe. Remarkably, they exhibit not only strong SHG effects, suitable band gap, large birefringence, broad IR transparency range and low two-photon absorption coefficients but reinforced interlayer interaction and more benign crystal growth habit, compared to those of GaSe, indicating that they are promising long-wave IR NLO materials. Moreover, Hg3AsSe4I achieved better comprehensive optical properties than conventional IR crystals, GaSe, ZnGeP2, CdSe and AgGaSe2. The idea of honeycomb layered topology construction provides a material design heuristic to explore cutting-edge IR NLO materials.

A hybrid halide lead-free pseudo-perovskite with large birefringence

A new 2D layered hybrid pseudo-perovskite, MLASnCl4(MLA = melamine), shows a large birefringence of up to 0.294@550 nm and excellent air stability.

Hg3O2(NO3)F: a mercury nitrate oxyfluoride with an unprecedented [(Hg3O2F)+]∞cationic framework and excellent optical anisotropy

A novel nitrate oxyfluoride, Hg3O2(NO3)F, shows an unprecedented [(Hg3O2F)+]∞cationic framework and a large birefringence (0.23@1064 nm).

Deep-ultraviolet nonlinear-optical crystal BaNa2[PO3(OH)]2 with large birefringence and strong second-harmonic-generation response

Deep-ultraviolet (DUV, λ ​< ​200 ​nm) nonlinear-optical (NLO) crystals play a pivotal role in modern laser science and technology. Metal phosphates have been considered as fascinating candidates for DUV NLO crystal material. However, how to generate both strong second-harmonic-generation (SHG) response and large birefringence for promising DUV NLO metal phosphates is a long-standing issue. Herein, a new DUV NLO metal phosphate, BaNa2[PO3(OH)]2, was successfully synthesized, which features a two-dimensional [NaPO3(OH)]∞ alveolate layer alternately connected by highly asymmetric [PO3(OH)] groups and NaO5 triangular bipyramids. BaNa2[PO3(OH)]2 can realize a good balance of DUV nonlinear properties covering short UV absorption edge less than 190 ​nm, strong SHG response with the magnitude of ∼1.2 ​× ​benchmark KH2PO4 (KDP), and the largest birefringence with the experimental value of 0.064@590 ​± ​3 ​nm in reported alkaline/alkaline-earth metal phosphates, producing the shortest phase-matching output down to the wavelength of 164 ​nm. These research results show that BaNa2[PO3(OH)]2 crystal is a potential DUV NLO crystal material.

K5[B3O3F4(OH)]2(NO3): the first hydroxyfluorooxoborate-nitrate with a short ultraviolet cutoff edge and large birefringence.

The first hydroxyfluorooxoborate-nitrate mixed anion compound, K5[B3O3F4(OH)]2(NO3), was synthesized by the solution evaporation method. It displays a unique structure built by K+ cations, the hydroxylated and fluorinated six-membered ring [B3O3F4(OH)] and [NO3] groups. It possesses a band gap of 5.68 eV derived from the diffuse reflectance spectrum, which corresponds to an ultraviolet cutoff edge of 218 nm. First-principles calculations show that it has a large birefringence of 0.095 at 532 nm and the result of the response electron distribution anisotropy method indicates that all three anion groups contribute positively to the birefringence, verifying the synergic contributions from the multiple anion groups.

A0.5H2C6N7O3·4H2O (A = Ca2+, Sr2+) iso-cyamelurates with ultra-large π-conjugated group and excellent nonlinear optical properties

Two isocyamelurates of A0.5H2C6N7O3·4H2O (A= Ca2+, Sr2+) were successfully synthesized. Both of them showed excellent properties of wide band gap, large birefringence, and strong second order harmonic generation response.

An effective pathway to design and synthesize UV birefringent crystalsviarational assembly of π-conjugated [CO3]2−and [NO3]−triangles

Na3Rb6(CO3)3(NO3)2X·6H2O has the potential to serve as an excellent UV birefringent crystal due to its large birefringence and wide band gap.

C10H10ClNO3: exploration of birefringent crystals in an isoquinoline system

An organic–inorganic hybrid material of C10H10ClNO3exhibits a large experimental birefringence value of 0.345@550 nm, resulting from the new birefringence-active structural gene of expanded planar [C10H8NO2]+groups.

Constructing ultraviolet nonlinear optical crystals with large second harmonic generation and short absorption edges by using polar tetrahedral S2O3 groups

It is generally considered difficult for traditional sulfates to exhibit strong second harmonic generation (SHG) responses and large birefringence values because SO4 groups are nonpolar tetrahedral structures.

Ba3(BS3)(PS4): the first alkaline-earth metal thioborate-thiophosphate with strong optical anisotropy originating from planar [BS3] units.

The first alkaline-earth metal thioborate-thiophosphate Ba3(BS3)(PS4) was designed from Ba3(BO3)(PO4) by S-O substitution and fabricated experimentally. The [BS3] pseudo-layers formed in the structure contribute to the strong optical anisotropy and a large birefringence of ∼0.11 at 1064 nm. The results enrich the structural and chemical diversity of chalcogenides.

Low temperature molten salt synthesis of noncentrosymmetric (NH4)3SbF3(NO3)3and centrosymmetric (NH4)3SbF4(NO3)2

Two antimony nitrates were synthesized by the low temperature molten salt method. Both of them reveal large birefringence; especially, noncentrosymmetric (NH4)3SbF3(NO3)3exhibits a strong SHG coefficient of about 3.3×KDP.