Moderate Second Harmonic Generation Response Research Articles

Synthesis, crystal and electronic structures, linear and nonlinear optical properties, and photocurrent response of oxyhalides CeHaVIO4 (Ha = Cl, Br; VI = Mo, W).

Four heteroanionic oxyhalides, CeClMoO4, CeBrMoO4, CeClWO4, and CeBrWO4, have been studied as multifunctional materials, which show a combination of good second harmonic generation (SHG) response and photocurrent signals. Millimeter-sized CeHaVIO4 (Ha = Cl, Br; VI = Mo, W) crystals were grown by halide salt flux. The crystal structure of CeHaVIO4 crystals was accurately determined by single-crystal X-ray diffraction. CeClMoO4, CeBrMoO4, and CeBrWO4 are isostructural to each other, and crystallize in the acentric LaBrMoO4 structure type. CeClWO4 crystallizes in a new structure type with unit cell parameters of a = 19.6059(2) Å, b = 5.89450(10) Å, c = 7.80090(10) Å, and β = 101.4746(8)°. The bandgaps of CeHaVIO4 fall into the range of 2.8(1)-3.1(1) eV, which are much smaller than those of isotypic LaHaVIO4 (Ha = Cl, Br; VI = Mo, W) in the range of 3.9(1)-4.3(1) eV. The narrowing of bandgaps in CeHaVIO4 originates from the presence of partially filled 4f orbitals of cerium atoms, which was confirmed by density functional theory (DFT) calculations. The moderate bandgaps make CeHaVIO4 suitable for infrared nonlinear optical (IR NLO) applications. CeBrMoO4 and CeBrWO4 exhibit moderate SHG responses of 0.58× AGS and 0.46× AGS, respectively, and are both type-I phase-matching materials. Moderate SHG response, easy growth of crystals, high ambient stability, and type-I phase-matching behavior make CeBrMoO4 and CeBrWO4 great materials for IR NLO applications. CeHaVIO4 films also exhibited good photocurrent response upon light radiation. This work demonstrates the rich structural chemistry of the REHaVIO4 (RE = Y, La-Lu; Ha = Cl, Br; VI = Mo, W) family and the potential presence of more multifunctional materials.

Exploring a new short-wavelength nonlinear optical fluoride material featuring unprecedented polar cis-[Zr6F34]10- clusters.

Traditional fluorides are rarely reported as candidates for nonlinear optical (NLO) materials featuring a deep-ultraviolet cutoff edge. Theoretical investigations suggest that the ZrF8 dodecahedron shows large polarizability anisotropy and benefits for large birefringence. Herein, a new fluorine-rich fluoride, K3Ba2Zr6F31, was synthesized by coupling the ZrF8 group, featuring acentric cis-[Zr6F34]10- clusters with a 63-screw axis. Significantly, K3Ba2Zr6F31 exhibits a short UV cutoff edge (below 200 nm) and moderate second-harmonic generation (SHG) response (0.5 × KH2PO4). It also possesses a relatively large birefringence (0.08@1064 nm), together with a broad transparency window (2.5-21.1 μm). First-principles calculations suggest that the cis-[Zr6F34]10- cluster built by ZrF8 dodecahedra are the dominant contributors to the large band gap (7.89 eV, cal.) and SHG response simultaneously. Such systematic work highlights that Zr-based fluorides afford a new paradigm for the development of efficient NLO materials with a short UV cutoff edge.

Amine-directed synthesis, valence state control, and optical properties of two new organic-inorganic tin chlorides.

Two organic-inorganic tin chlorides, namely (C9H26N3Cl)SnCl4 (1) and (C9H26N3Cl)SnCl6 (2), were prepared via valence state control using N,N,N',N'',N''-pentamethyldiethylenetriamine as a structure-directing agent. The two compounds have zero-dimensional structures crystallized in non-centrosymmetric orthorhombic space group Cmc21 and P212121, respectively. In compound 1, the divalent tin ion forms a seesaw coordination configuration with four chloride ions, whereas in compound 2, the tetravalent tin ion forms an octahedral coordination configuration with six chloride ions. The two compounds show a moderate second-harmonic generation response under 1064 nm laser irradiation. Notably, compound 2 displays a bright orange luminescence with a photoluminescence quantum yield of 19.67%. Theoretical calculations were performed to gain insights into the optical properties of the two compounds.

Four UV Transparent Linear and Nonlinear Optical Materials Explored from Pure Selenite Compounds

AbstractUV nonlinear optical materials require the simultaneous achievement of a large second harmonic generation (SHG) coefficient (≥1 × KH2PO4 (KDP), dij > 0.39 pmV−1), wide bandgap (λ < 300 nm, Eg > 4.2 eV), and moderate birefringence (0.05‐0.10@1064 nm) in a single structure. Therefore, designing UV nonlinear optical materials with excellent comprehensive performance is a challenging task. Herein, four UV transparent selenite materials are successfully obtained, namely, Al2(SeO3)3(H2O)3 (1), Ga2(SeO3)3(H2O)3 (2), NaGa3(HSeO3)6(SeO3)2 (3), and Cd5Ga4(HSeO3)2(SeO3)10 (4), through rational design and screening in the pure selenite system. Al2(SeO3)3(H2O)3 (1) and Ga2(SeO3)3(H2O)3 (2) are UV nonlinear optical materials with balanced properties, exhibiting moderate SHG responses (1.2 and 1.1 × KDP), appropriate birefringence (0.084 and 0.076@1064 nm), and wide bandgaps (5.5 and 5.3 eV). Such bandgaps are the largest in the reported pure selenite nonlinear optical (NLO) materials. This work further demonstrates that pure selenite is a good candidate for UV NLO materials.

Modulating Two Pairs of Chiral DyIII Enantiomers by Distinct β-Diketone Ligands to Show Giant Differences in Single-Ion Magnet Performance and Nonlinear Optical Response.

Using Dy(dbm)3(H2O) and Dy(btfa)3(H2O)2 to react with enantiopure N-donors, (-)/(+)-4,5-pinenepyridyl-2-pyrazine (LR/LS), respectively, two pairs of chiral DyIII enantiomers, Dy(dbm)3LR/Dy(dbm)3LS (R-1-Dy/S-1-Dy) and Dy(btfa)3LR/Dy(btfa)3LS (R-2-Dy/S-2-Dy) were obtained, wherein one of the benzene rings of dbm- (dibenzoylmethanate) in R-1-Dy/S-1-Dy is displaced by the -CF3 group of btfa- (4,4,4-trifluoro-1-phenyl-1,3-butanedionate) in R-2-Dy/S-2-Dy. Interestingly, this substitution results not only in giant differences in their single-ion magnetic (SIM) performances but also in their completely different nonlinear optical (NLO) responses. R-1-Dy presents a large effective energy barrier (Ueff = 265.47 K) under zero applied field, being more than 4 × R-2-Dy (61.40 K). The discrepancy on their magnetic performances has been further elucidated by ab initio calculations. Meanwhile, R-1-Dy/S-1-Dy display the strongest third-harmonic generation responses (35/33 × α-SiO2) among the known lanthanide NLO-active coordination compounds (CCs). On the contrary, R-2-Dy/S-2-Dy exhibit moderate second-harmonic generation responses (0.65/0.70 × KDP). These results not only give the first example of the CCs with both SMM/SIM behavior and a THG response but also provide an efficient strategy for achieving the function regulation and switch in multifunctional CCs.

Design of a diamond-like infrared nonlinear optical material LiBS2 with ultra-wide band gap

The exploration of new infrared (IR) nonlinear optical (NLO) materials with large second-harmonic generation (SHG) responses and wide band gap (Eg) is an urgent need but challenging. Starting from the superior unit combination strategy and considering the advantages of borates, chalcogenides and Li elements, we have focused our attention on the exploration of IR NLO materials in the Li-based thioborates. Four novel non-centrosymmetric LiBS2 structures, were obtained successfully through crystal structure prediction by analogy and structural optimization based on the thermodynamic and dynamic stability analysis. Among them, LiBS2-I exhibits an ultra-wide band gap Eg = 4.4 eV, moderate SHG response 0.6 × AgGaS2, and suitable birefringence Δn = 0.04 at 1064 nm, which satisfies the good balance between Eg ≥ 3.0 eV and dij ≥ 0.5 × AgGaS2. The role of microscopic units [BS4] in NLO effect was investigated. This work enriches the structural diversity of thioborates and provides a new approach to the exploration of excellent IR NLO materials.

AAg3Ga8Se14 (A = Rb, Cs): second-harmonic generation responses realized through the parallel arrangement of AgSe4 and GaSe4 tetrahedrons.

Two new quaternary selenides AAg3Ga8Se14, (A = Rb, 1; Cs, 2) were synthesised via solid-state reaction in sealed silica tubes. Compounds 1 and 2 crystallised in the monoclinic space group Cm (no. 8) and their three-dimensional [Ag3Ga8Se14]- anionic frameworks were comprised of AgSe4 and GaSe4 tetrahedrons. Their UV-Vis-near infrared diffuse reflectance spectra showed that 1 and 2 possessed wide band gaps of 2.17 and 2.10 eV, respectively. Notably, under incident laser irradiation at 1910 nm, compounds 1 and 2 presented moderate second-harmonic generation responses of 0.6 and 0.7 × AgGaS2, respectively, with phase-matching behaviours due to the parallel arrangement of nonlinear optical (NLO) functional tetrahedral AgSe4 and GaSe4 units. The laser-induced damage thresholds of 1 and 2 were estimated to be 25.4 and 18.0 MW cm-2, respectively, which were 2.1 and 1.5 times the threshold of AgGaS2. This study revealed that the title selenides, which were constructed from tetrahedral units arranged in a parallel array, are promising infrared NLO materials.

Noncentrosymmetric (KBa0.5)In2Se4 and (K0.58Ba0.71)(Ga0.89In1.11)Se4 derived from centrosymmetric BaIn2Se4 via partial cation substitution: structural chemistry and nonlinear optical activity

Two new noncentrosymmetric multinary selenides, (KBa0.5)In2Se4 (1) and (K0.58Ba0.71)(Ga0.89In1.11)Se4 (2), have been synthesized using a high-temperature flux method at 1123 K. They crystallize in the tetragonal noncentrosymmetric space group I4cm with cell parameters: a = 8.0277(2), c = 6.7654(3) Å, V = 435.99(3) Å3 for 1; a = 8.0296(4), c = 6.5403(9) Å, V = 421.68(7) Å3 for 2 vs the orthorhombic centrosymmetric space group Fddd for BaIn2Se4. Their one-dimensional structures are constructed by [(MSe2)–]n (M = Ga, In) chains composed of MSe4 tetrahedra via sharing edges, and K+/Ba2+ cation occupying the interchain cavities. They both show moderate second-harmonic generation responses about 0.5 × AgGaS2@2.1 μm. UV-vis-NIR diffuse reflectance spectroscopy measurement shows that the optical band gaps of 1 and 2 are about 2.60 and 2.34 eV, respectively. Theoretical calculations are also carried out to analyze their electronic structures and optical properties.

Rational Crystal Structure Design and Nonlinear-Optical Properties of Noncentrosymmetric RbCu2NbS4.

Crystal structure design based on known materials is an efficient strategy for exploring new compounds with evident second-harmonic-generation (SHG) effects. By the introduction of Rb+ ions into the 3D framework of Cu3NbS4, the new compound RbCu2NbS4 (space group Ama2) composed of layers is obtained. The band gap of RbCu2NbS4 is 2.1 eV, indicating that this compound is a semiconductor. Band-structure calculations indicate that the electronic transition mainly occurs from the S 3p/Cu 3d to Nb 4d states. The intercalation of Rb+ ions induces a high degree of local distortion and symmetry reduction, which results in a dipole moment of 11.7 Debye for RbCu2NbS4. RbCu2NbS4 shows a moderate SHG response of 0.33 × AgGaS2 (particle size of 20-41 μm).

Explorations of Second-Order Nonlinear Optical Materials in the Alkaline Earth Barbiturate System: Noncentrosymmetric Ca(H3C4N2O3)2·H2O and Centrosymmetric Sr(H5C8N4O5)2·4H2O.

Two new alkaline earth barbiturates, Ca(H3C4N2O3)2·H2O and Sr(H5C8N4O5)2·4H2O, were synthesized via the mild hydrothermal technique. For Ca(H3C4N2O3)2·H2O, the stacking (H3C4N2O3)- anions along the c axis are interconnected by CaO7 polydedra forming a three-dimensional structure. Also, for Sr(H5C8N4O5)2·4H2O, it has two-dimensional layers composed by SrO7 polyhedra and (H5C8N4O5)- anions. The (H5C8N4O5)- anions can be seen as two (H3C4N2O3)- anions connected each other via the N-C bond. Powder second-harmonic generation (SHG) measurements revealed that Ca(H3C4N2O3)2·H2O is a phase-matchable material with a moderate SHG response (ca. 1.15× that of KDP). Furthermore, the birefringence values of the two crystals were measured as 0.49 and 0.475 at 546.1 nm, respectively. The theoretical calculations showed that the SHG response and large birefringence were primarily caused by the (H3C4N2O3)- and (H5C8N4O5)- groups.

A highly distorted HgS4 tetrahedron-induced moderate second-harmonic generation response of EuHgGeS4

The first Eu,Hg-based chalcogenide EuHgGeS4 exhibits phase-matchable SHG activity with an intensity ∼0.9 times that of AgGaS2.

Synthesis, characterization, and theoretical analysis of three new nonlinear optical materials K7MRE2B15O30 (M= Ca and Ba, RE= La and Bi)

Three new complex borate compounds K7CaBi2B15O30, K7CaLa2B15O30 and K7BaBi2B15O30 have been synthesized by the high-temperature solution method. K7CaLa2B15O30 and K7CaBi2B15O30 crystallize in the chiral trigonal space group R32, while K7BaBi2B15O30 crystallizes in the noncentrosymmetric orthorhombic polar space group Pca21. All of the title compounds have similar three-dimensional crystal structures, which are composed of isolated B5O10 groups and LaO6 or BiO6 octahedra, and K+, Ca2+, and Ba2+ cations fill into the cavities to keep charge balance. Based on our research, in the system of K7MIIRE2B15O30 (MII = Ca, Sr, Ba, Zn, Cd, Pb, K/RE0.5; RE = Sc, Y, La, Gd, Lu, Bi), K7BaBi2B15O30 is unique and crystallizes in a different space group, which enriches the structural chemistry of borate. Detailed structural analyses indicate that the structural variation is due to the difference in size and coordination number of the alkaline-earth metal cations. Besides, UV-Vis-NIR spectroscopy analysis and the second-harmonic generation (SHG) measurement on the powder samples show that K7CaBi2B15O30 exhibits a UV cutoff edge (about 282 nm) and a moderate SHG response (about 0.6 × KDP). In addition, thermal analysis and infrared spectroscopy were also presented. To better understand the structure-property relationships of the title compounds, the first-principles calculations have been performed.

Module-Guided Design Scheme for Deep-Ultraviolet Nonlinear Optical Materials.

Design of functional materials with targeted properties is a challenge because of the diversity of their potential structures. The functional performances of materials are mainly determined by the chemistry and electronic structure of modules consisting of local atomic groups with special arrangements. Tetrahedral modules are excellent modules for designing deep-ultraviolet/ultraviolet (UV) nonlinear optical (NLO) materials, but they are rarely favored due to their unpredictable optical anisotropy and second harmonic generation (SHG) response. In this work, we have developed a module-guided ab initio approach for evaluating the optical anisotropy of tetrahedral modules. The application of this method indicates that the tetrahedral modules with a specific arrangement will enhance the optical anisotropy of materials. With the functional modules consisting of tetrahedral modules and rare-earth cations, new high-performance rare-earth phosphates were assembled. These materials are promising deep-UV NLO materials because of their appropriate birefringences, large band gaps, moderate SHG responses, and easy to obtain large size crystals.

K2ZnGe3S8: A Congruent-Melting Infrared Nonlinear-Optical Material with a Large Band Gap.

K2ZnGe3S8 belonging to the noncentrosymmetric space group P21 of the monoclinic system was discovered via a solid-state method. It possesses two-dimensional [ZnGe3S8]2- layers, with alkali-metal cations K+ located between the layers. On the basis of UV-vis-near-IR diffuse-reflectance spectrometry, the band gap of K2ZnGe3S8 is 3.36(2) eV. According to powder second-harmonic-generation (SHG) measurements, the SHG response of K2ZnGe3S8 is about 0.9 times that of AgGaS2 at the particle size range of 20-41 μm. Experimental results demonstrate that K2ZnGe3S8 keeps a good balance between a large band gap (3.36 eV) and a moderate SHG response. Moreover, according to the differential scanning calorimetry measurements, K2ZnGe3S8 melts congruently at around 1023 K and recrystallizes at about 963 K. Therefore, it is possible to obtain bulk single crystals via the Bridgman-Stockbarger method. The first-principles calculations indicate that the optical properties of K2ZnGe3S8 are dominantly determined by the [GeS4] tetrahedra as well as a small contribution from the [ZnS4] tetrahedra.

Ba4B8TeO19: A UV Nonlinear Optical Material

We report a new noncentrosymmetric barium tellurium borate, Ba4B8TeO19 that has potential ultraviolet (UV) nonlinear optical (NLO) applications. Ba4B8TeO19 was synthesized by a flux method and crystallizes in the noncentrosymmetric space group Cc. The material exhibits a framework structure of [B8O17]∞ double layers connected to distorted TeO6 octahedra. Second harmonic generation (SHG) measurements at 1064 and 532 nm on polycrystalline Ba4B8TeO19 indicate that the title compound is phase-matchable (type I) with a moderate SHG response (1 × KH2PO4 at 1064 nm and 0.2 × β-BaB2O4 at 532 nm). In addition, a short absorption edge (210 nm) was measured. Using density functional theory calculations, we show that the SHG response originates from contributions from O 2p and Te 5s states at the valence and conduction band edges. Finally, by computing the linear optical properties, we find that this compound displays a moderate birefringence of 0.055 at 1064 nm and 0.059 at 532 nm, necessary conditions for phase-matching in UV NLO materials.

Li8NaRb3(SO4)6·2H2O as a new sulfate deep-ultraviolet nonlinear optical material

A new sulfate Li8NaRb3(SO4)6·2H2O exhibits a short cutoff edge belowλ< 190 nm and has a moderate second-harmonic generation response in type-I phase-matchable behavior.

First-Principles Assisted Prediction of the Nonlinear Optical Behavior of Mg3B7O13Cl Crystal

In order to explore new nonlinear optical (NLO) crystals with superior performance, it is greatly desirable to understand the intrinsic relationship between the microscopic structural features and macroscopic optical properties of crystals. In this paper, the electronic structures and optical properties of Mg3B7O13Cl (MBOC), which contains B7O13 functional building blocks, were investigated to understand the structure — optical property relationship by first-principles calculation. Our calculated results show that the large band gap and the moderate second-harmonic generation (SHG) coefficient of MBOC (8.43 eV and d32 = 0.41 pm/V) are comparable to those of KBe2BO3F2 (8.64 eV and d11 = 0.46 pm/V). The origin of the large band gap and the moderate SHG response of MBOC were explained by combining electronic structure analysis and the SHG density method.

Thermal Expansion and Second Harmonic Generation Response of the Tungsten Bronze Pb2AgNb5O15.

The incorporation of transition metal element Ag was performed to explore negative thermal expansion (NTE) materials with tetragonal tungsten bronze (TTB) structures. In this study, the structure and thermal expansion behaviors of a polar TTB oxide, Pb2AgNb5O15 (PAN), were systematically investigated by high-resolution synchrotron powder diffraction, high-resolution neutron powder diffraction, transmission electron microscope (TEM), and high-temperature X-ray diffractions. The TEM and Rietveld refinements revealed that the compound PAN displays (√2a(TTB), √2b(TTB), 2c(TTB))-type superstructure. This superstructure within the a-b plane is caused by the ordering of A-site cations, while the doubling of the c axis is mainly induced by a slight tilt distortion of the NbO6 octahedra. The transition metal Ag has larger spontaneous polarization displacements than Pb, but the Pb-O covalence seems to be weakened compared to the potassium counterpart Pb2KNb5O15 (PKN), which may account for the similar Curie temperature and uniaxial NTE behavior for PAN and PKN. Powder second harmonic generation (SHG) measurement indicates that PAN displays a moderate SHG response of ∼0.2 × LiNbO3 (or ∼100 × α-SiO2) under 1064 nm laser radiation. The magnitudes of the local dipole moments in NbO6 and PbOx polyhedra were quantified using bond-valence approach. We show that the SHG response stems from the superposition of dipole moments of both the PbO(x) and NbO6 polyhedra.

K2Pb3(CO3)3F2 and KCdCO3F: Novel Fluoride Carbonates with Layered and 3D Framework Structures.

Two new mixed metal fluoride carbonates, KCdCO3F and K2Pb3(CO3)3F2, have been synthesized by solvothermal and solid-state techniques. KCdCO3F crystallizes in the acentric nonpolar space group P6̅m2, and its structure features a three-dimensional anionic framework in which the CdCO3 layers are further interconnected by bridging F(-) anions with the negative charge balanced by K(+) cations. K2Pb3(CO3)3F2 crystallizes in the centrosymmetric space group P63/mmc, and its structure exhibits a layered anionic skeleton featuring corner-shared PbO6F and PbO6F2 polyhedra. UV-vis diffuse reflectance spectroscopy studies show that the short-wavelength absorption edges of KCdCO3F and K2Pb3(CO3)3F2 are 227 and 287 nm, respectively. The second harmonic generation (SHG) measurement reveals that KCdCO3F is a phase-matchable material for generation of doubled-frequency light at both 532 and 266 nm, with a large SHG response of approximately 5.2 times that of KH2PO4 (KDP) at 532 nm and a moderate SHG response of approximately 0.75 times that of β-BaB2O4 (BBO) at 266 nm. Therefore, it is a promising UV material for fourth harmonic generation on a 1064 nm Q-switched Nd:YAG laser.

New Second-Order NLO Materials Based on Polymeric Borate Clusters and GeO4 Tetrahedra: A Combined Experimental and Theoretical Study

Three novel rubidium borogermanates with three types of noncentrosymmetric structures, namely, RbGeB(3)O(7), Rb(2)GeB(4)O(9), and Rb(4)Ge(3)B(6)O(17), have been synthesized by high-temperature solid-state reactions in platinum crucibles. The structure of RbGeB(3)O(7) features a three-dimensional (3D) anionic framework composed of cyclic B(3)O(7) groups corner-sharing GeO(4) tetrahedra. The structure of Rb(2)GeB(4)O(9) shows a 3D anionic framework based on B(4)O(9) clusters connected by GeO(4) tetrahedra via corner sharing. The structure of Rb(4)Ge(3)B(6)O(17) is a novel 3D anionic framework composed of cyclic B(3)O(8) groups, Ge(2)O(7) dimers, and GeO(4) tetrahedra that are interconnected via corner sharing. Second harmonic generation (SHG) measurements indicate that RbGeB(3)O(7), Rb(2)GeB(4)O(9), and Rb(4)Ge(3)B(6)O(17) display moderate SHG responses that are approximately 1.3, 2.0, and 1.3 × KH(2)PO(4) (KDP), respectively, which are slightly smaller than those from theoretical calculations (about 3.7, 2.8, and 2.4 × KDP, respectively).