deep-UV Nonlinear Optical Materials Research Articles

Synthesis and characterization of a new beryllium-free deep-ultraviolet nonlinear optical material: Na2GdCO3F3

A new noncentrosymmetric (NCS) material, namely, Na2GdCO3F3 has been obtained using the hydrothermal method. Na2GdCO3F3 exhibits an intricate three-dimensional structure that is composed of NaO4F2, NaO2F4 and GdO3F6 distorted polyhedra and planar [CO3] triangles. Powder second-harmonic generation (SHG) using the Kurtz−Perry technique shows that Na2GdCO3F3 is type I phase-matchable, and the measured SHG coefficient was 2.0 times that of KH2PO4(KDP). The result from the UV–vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edge was below 200 nm, suggesting that Na2GdCO3F3 is a promising deep-UV nonlinear optical material.

Deep-Ultraviolet Transparent Cs2LiPO4 Exhibits an Unprecedented Second Harmonic Generation

Developing superior deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials is a great challenge because of the contradiction between deep-UV transparency and enhanced second harmonic generation (SHG), especially for deep-UV NLO phosphates in which the constituent P–O groups have relatively small microscopic SHG coefficients. Here we report a new noncentrosymmetric phosphate Cs2LiPO4 (I), whose crystal structure consists of [LiPO4]∞ layered structural units with a novel honeycomb-like topology. As compared with the benchmark deep-UV NLO material KBe2BO3F2, I is beryllium-free, and it is relatively easy to grow its large single crystals because of its congruent melting. Furthermore, it not only is deep-UV transparent but also exhibits an unexpectedly enhanced SHG response of 1.8 × KH2PO4 that hits a new high in deep-UV NLO phosphates. These results demonstrate that I satisfies the key requirements of being a promising deep-UV NLO candidate. Theory calculations and structural analysis reveal that the enhanced SHG response can be attributed to the honeycomb-like topological structure, which endows the constituent [PO4]3– monomers of I with an aligned arrangement and as a result a favorable superposition of their microscopic SHG coefficients. These findings may provide useful insights into the development of both deep-UV NLO materials and honeycomb-like topological structures.

ChemInform Abstract: Deep Ultraviolet Nonlinear Optical Materials

AbstractReview: 185 refs.

Deep Ultraviolet Nonlinear Optical Materials

Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Deep‐Ultraviolet Nonlinear Optics in a Borate Framework with 21‐Ring Channels

A new borate LiBa3 (OH)[B9 O16 ][B(OH)4 ], which combines the uniform porosity of open-frameworks with the extraordinary NLO properties of borates, has been obtained under hydrothermal conditions by using mixed lithium and barium ions as templates. The framework displays an acs-type net with large 21-ring channels. The second harmonic generation (SHG) measurement shows that it is a type I phase-matchable material with a strong SHG signal intensity about 3.1 times that of KDP (KH2 PO4 ). UV/Vis-NIR diffuse reflectance analysis indicates that the compound has a wide transparency range with the short-wavelength absorption edge below 200 nm. These characteristics reveal that the compound is a promising deep-UV nonlinear optical material.

Designing a Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material without a Structural Instability Problem.

A beryllium-free deep-ultraviolet (deep-UV) nonlinear optical (NLO) material K3Ba3Li2Al4B6O20F is developed mainly by the element substitution of Be for Al and Li from Sr2Be2B2O7 that was considered as one of the most promising deep-UV NLO materials. K3Ba3Li2Al4B6O20F preserves the structural merits of Sr2Be2B2O7 and thus exhibits no layering growth tendency and possesses the optical properties required for deep-UV NLO applications, including deep-UV transparency, phase-matchability, and sufficiently large second-harmonic generation (1.5 × KH2PO4). Furthermore, it overcomes the structural instability problem of Sr2Be2B2O7, which is confirmed by the obtainment of large single crystals and phonon dispersion calculations. These attributes make it very attractive for next-generation deep-UV NLO materials. The substitution of Be for Al and Li in beryllium borates provides a new opportunity to design beryllium-free deep-UV NLO materials with good performance.

Synthesis and characterization of CsSrCO3F – a beryllium-free new deep-ultraviolet nonlinear optical material

A noncentrosymmetric fluoride carbonate CsSrCO3F has been synthesized which is a promising beryllium-free deep-UV nonlinear optical material.

Sr2(OH)3NO3: the first nitrate as a deep UV nonlinear optical material with large SHG responses

A noncentrosymmetric nitrate Sr2(OH)3NO3 has been synthesized which is the first nitrate as a promising deep-UV nonlinear optical material.

An acentric calcium borate Ca2[B5O9]·(OH)·H2O: synthesis, structure, and nonliner optical property.

A novel noncentrosymmetric calcium borate, Ca2[B5O9]·(OH)·H2O (1), was synthesized under solvothermal condition using mixed solvents of pyridine and H2O. Compound 1 crystallizes in the monoclinic space group Cc. Its structure contains [B5O12] units and features a three-dimensional (3D) pcu net with nine-membered ring (9-MR) channels along the b-axis, where the Ca(2+) cations, OH(-) ions, and H2O molecules are located. Each Ca polyhedron shares three edges and one vertex with four neighbors to form a 3D dia Ca-O network. The pcu B-O net and dia Ca-O net are further interpenetrated to give the final denser net. The second harmonic generation (SHG) measurement shows that compound 1 is a type I phase-matchable material with a strong SHG response of ∼3 times that of KH2PO4. In addition, it exhibits a wide transparency range with a short UV cutoff edge below 200 nm. These results reveal that the compound is a potential deep-UV nonlinear optical material. The Vienna ab initio theoretical studies indicate the good SHG response is derived from the synergistic effect of the π-conjugated systems of BO3 groups and distorted CaO9 polyhedra.

Deep-ultraviolet transparent phosphates RbBa2(PO3)5 and Rb2Ba3(P2O7)2 show nonlinear optical activity from condensation of [PO4](3-) units.

It is challenging to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance between deep-UV transparency and high NLO activity. Known deep-UV NLO materials are almost exclusively limited to borates, except few newly discovered phosphates despite their small NLO activities. Here we report two asymmetric phosphates, RbBa2(PO3)5 (I) and Rb2Ba3(P2O7)2 (II), which feature [PO3]∞ chains and [P2O7](4-) dimers formed by condensation of [PO4](3-) units, respectively. Remarkably, I achieves the desired balance, with the shortest deep-UV absorption edge at 163 nm and the largest NLO activity of 1.4 × KDP (KH2PO4) in deep-UV NLO phosphates. According to first-principles calculations, the enhanced macroscopic SHG response of I can be attributed to the [PO3]∞ chains which exhibit significantly larger microscopic SHG coefficients as compared with the [P2O7](4-) dimers.

Ba4(BO3)3(SiO4)·Ba3X (X = Cl, Br): new salt-inclusion borosilicate halides as potential deep UV nonlinear optical materials

Based on the combination of two different anionic groups (SiO4 and BO3) and the utility of a XBa6 (X = Cl, Br) polar template, two new salt-inclusion compounds, Ba4(BO3)3(SiO4)·Ba3X (X = Cl, Br) have been successfully synthesized by the high-temperature solution method for the first time. They are isostructural and their structures feature the ∞3[Ba4(BO3)3(SiO4)] framework with 1D channels along the c axis, in which resided the polar ∞1[Ba3X] chains. It is worth noting that they are the first alkaline-earth metal borosilicate halides to be used as nonlinear optical (NLO) materials. The second harmonic generation (SHG) measurements show that they have SHG responses similar to that of KH2PO4 (KDP) and are type-I phase-matchable. In addition, they melt congruently and exhibit a wide transparent region with the UV cut-off edge below 190 nm. These properties make Ba4(BO3)3(SiO4)·Ba3X potential deep UV NLO materials.

Deep-Ultraviolet Nonlinear Optical Materials: Na2Be4B4O11 and LiNa5Be12B12O33

Deep-UV coherent light generated by nonlinear optical (NLO) materials possesses highly important applications in photonic technologies. Beryllium borates comprising anionic planar layers have been shown to be the most promising deep UV NLO materials. Here, two novel NLO beryllium borates Na2Be4B4O11 and LiNa5Be12B12O33 have been developed through cationic structural engineering. The most closely arranged [Be2BO5]∞ planar layers, connected by the flexible [B2O5] groups, have been found in their structures. This structural regulation strategy successfully resulted in the largest second harmonic generation (SHG) effects in the layered beryllium borates, which is ~1.3 and 1.4 times that of KDP for Na2Be4B4O11 and LiNa5Be12B12O33, respectively. The deep-UV optical transmittance spectra based on single crystals indicated their short-wavelength cut-offs are down to ~170 nm. These results demonstrated that Na2Be4B4O11 and LiNa5Be12B12O33 possess very promising application as deep-UV NLO crystals.

A novel deep UV nonlinear optical crystal Ba3B6O11F2, with a new fundamental building block, B6O14 group

Single crystals of Ba3B6O11F2 have been synthesized by introducing the F− anion into the BaO-B2O3 system and the structure was determined by single-crystal X-ray diffraction. It crystallizes in the non-centrosymmetric space group P21 (no. 4). In the structure, a new fundamental building block, the B6O14 group, was observed. The second harmonic generation (SHG) measurement shows that Ba3B6O11F2 possesses a large SHG response about three times that of KH2PO4 (KDP) and is phase-matchable. In addition, it exhibits a wide transparency range with a short UV cut-off edge (<190 nm), which suggests that the material is a potential deep UV nonlinear optical material.

X-ray and neutron diffraction studies of flux and hydrothermally grown nonlinear optical material KBe2BO3F2

Deep-UV nonlinear optical material KBe2BO3F2 (KBBF), fabricated by flux and hydrothermal methods, are studied by single crystal and powder X-ray diffraction (XRD) and neutron diffraction (NPD). Based on the single crystal diffraction data, the standard R32 structure is confirmed for flux grown KBBF, while the Rc structure is identified for the hydrothermally grown KBBF. No clear evidence of hydrogen bonding is found in the crystals by single crystal neutron diffraction. From powder XRD and neutron diffraction, the hydrothermally grown KBBF under investigation is found to be a mixture of two components consisting of 19.8 wt% of the R32 structure and 80.2 wt% of the Rc structure. No phase changes as a function of temperature up to 775 °C are observed for both samples from temperature dependent powder XRD data. However, a large anisotropic thermal expansion of the lattice is shown in the temperature dependent data.

A congruently melting and deep UV nonlinear optical material: Li3Cs2B5O10

Single crystals of Li3Cs2B5O10 have been synthesized and its structure determined by single-crystal X-ray diffraction. Li3Cs2B5O10 crystallizes in the non-centrosymmetric space group C222(1) ( No. 20). The structure consists of isolated B5O10 groups that are bridged by LiOn (n = 4, 5) and CsOn (n = 8, 10) polyhedra through their vertex oxygen atoms to form an infinite three-dimensional structure. Li3Cs2B5O10 melts congruently and exhibits a short-wavelength absorption onset at 175 nm. As-prepared Li3Cs2B5O10 is both non-centrosymmetric and phase matchable as supported by second harmonic generation measurements.