Jiyong Yao

NaSr3Be3B3O9F4: a promising deep-ultraviolet nonlinear optical material resulting from the cooperative alignment of the [Be3B3O12F](10-) anionic group.

The demand for deep-ultraviolet (deep-UV) coherent light sources (l< 200 nm) has become increasingly urgent because they have important applications in semiconductor photolithography, laser micromachining, modern scientific instruments (super-high-resolution and angle-resolved photoemission spectrometer, for example) and so forth. To date, the most effective method to generate deep-UV coherent light with solid-state lasers is through cascaded frequency conversion, in particular multiharmonics, using deep-UV nonlinear optical (NLO) crystals. Therefore, the discovery of suitable deep-UV NLO crystals is of great importance. In the past decades, the anionic group theory, which reveals that the overall nonlinearity of a crystal is the geometrical superposition of the microscopic second-order susceptibility tensors of the NLO-active anionic groups, has been very successful in developing borate NLO crystals. Several important NLO crystals have been discovered, including b-BaB2O4 (BBO), [4] LiB3O5 (LBO), [5] CsB3O5 (CBO), CsLiB6O10 (CLBO), [7, 8] and YCa4O(BO3)3 (YCOB), which have been widely used in NLO optics. However, they cannot be used to generate deep-UV coherent light (l< 200 nm) by multiharmonic generation owing to some inherent shortcomings. Thus, the search for new NLO materials, particularly for deep-UVapplications, has attracted considerable attention. A deep-UV NLO material must have a very short absorption edge, and in this respect, beryllium borates are attractive as they are supposed to possess very large energy gap. It is also well known that the incorporation of fluorine can effectively cause the UV absorption edge of a crystal to blue-shift, so our group has made great efforts to search for new deep-UV NLO fluorine beryllium borate crystals. After more than ten years of intensive research in our group, the KBe2BO3F2 [16–18] (KBBF) crystal became the first practically usable deep-UV NLO crystal used to generate coherent 177.3 and 193 nm light. The excellent NLO properties of KBBF crystals are mainly determined by the (Be2BO3F2)1 layer made up of trigonal-planar [BO3] units and the tetrahedral [BeO3F] units. This deep-UV coherent light material has been used as a photon source in modern instruments and revealed many novel scientific phenomena which could not be observed by traditional techniques, as shown in the study of superconductor CeRu2 [19] and Bi2Sr2CaCu2O8+d. [20] Unfortunately, the KBBF crystal is very difficult to grow in thickness because of its strong layering tendency, which severely limits the coherent output power. Therefore, there is great demand for new types of fluorine beryllium borates which have deepUV transmission, moderate birefringence, and relatively large second harmonic generation (SHG) coefficients, and at the same time overcome the crystal-growth problems found in the KBBF crystal. Alkali-metal and alkaline-earth-metal cations are favorable for the transmission of UV light because there are no d–d electron or f–f electron transitions in this spectral region. As shown in numerous explorations, the size and charge of cations have great influence on the macroscopic packing of anions, which in turn determines the overall NLO properties in a crystal. 22] Herein, we utilize both alkali-metal and alkaline-earth-metal cations. Different charge/size combinations of mixed cations may have different influences on the packing of anions, so it is more likely to isolate new phases with interesting stoichiometries, structures, and properties. To date, no fluorine beryllium borates with mixed cations have been reported. Guided by this idea, we successfully obtained a new alkali-metal/alkaline-earth-metal fluorine beryllium borate NaSr3Be3B3O9F4, which contains the novel anionic group [Be3B3O12F] 10 as the basic building unit. Furthermore, the arrangement of these [Be3B3O12F] 10 groups is very favorable for generating large a NLO response and moderate birefringence and especially for avoiding the layering tendency during bulk crystal growth. Herein, we report the synthesis, crystal growth, structure, linear and nonlinear optical properties, thermal behavior, and electronic structure of NaSr3Be3B3O9F. These results indicate that the NaSr3Be3B3O9F4 crystal may be a promising NLO material in the deep-UV range. NaSr3Be3B3O9F4 [23] crystallizes in the noncentrosymmetric trigonal space group R3m. The crystal structure is depicted in Figure 1a. In the asymmetric unit, Sr, Na, Be, B each occupy one crystallographically unique position, and there are two unique F and O positions. The B atom is coordinated to three O atoms to form a planar BO3 unit with B O bond lengths [*] H. Huang, J. Yao, Z. Lin, X. Wang, R. He, W. Yao, N. Zhai, Prof. C. Chen Center for Crystal Research and Development Technical Institute of Physics and Chemistry Chinese Academy of Sciences, Beijing 100190 (China) E-mail: cct@mail.ipc.ac.cn

BaGa4Se7: A New Congruent-Melting IR Nonlinear Optical Material

The new compound BaGa(4)Se(7) has been synthesized for the first time. It crystallizes in the monoclinic space group Pc with a = 7.6252 (15) Å, b = 6.5114 (13) Å, c = 14.702 (4) Å, β = 121.24 (2)°, and Z = 2. In the structure, GaSe(4) tetrahedra share corners to form a three-dimensional framework with cavities occupied by Ba(2+) cations. The material is a wide-band gap semiconductor with the visible and IR optical absorption edges being 0.47 and 18.0 μm, respectively. BaGa(4)Se(7) melts congruently at 968 °C and exhibits a second harmonic generation response at 1 μm that is approximately 2-3 times that of the benchmark material AgGaS(2). A first-principles calculation of the electronic structure, linear and nonlinear optical properties of BaGa(4)Se(7) was performed. The calculated birefractive indexΔn = 0.08 at 1 μm and the major SHG tensor elements are: d(11) = 18.2 pm/V and d(13) = -20.6 pm/V. This new material is a very promising NLO crystal for practical application in the IR region.

Metal Thiophosphates with Good Mid-infrared Nonlinear Optical Performances: A First-Principles Prediction and Analysis

The family of metal thiophosphates is an important but long-ignored compound system of the nonlinear optical (NLO) materials with desirable properties for the mid-infrared (mid-IR) coherent light generation. In the present work, the mid-IR NLO capabilities of metal thiophosphate crystals are systematically investigated based on their structure-property relationship. The linear and nonlinear optical properties of these crystals are predicted and analyzed using the first-principles calculations. In particular, several metal thiophosphate compounds are highlighted to exhibit good mid-IR NLO performances, as supported by the primary experimental results. These candidates would greatly promote the development of the mid-IR NLO functional materials.

Synthesis, Structure, and Properties of Li2In2MQ6 (M = Si, Ge; Q = S, Se): A New Series of IR Nonlinear Optical Materials

The four isostructural compounds Li(2)In(2)MQ(6) (M = Si, Ge; Q = S, Se) have been synthesized for the first time. They crystallize in the noncentrosymmetric monoclinic space group Cc with the three-dimensional framework composed of corner-sharing LiQ(4), InQ(4), and MQ(4) tetrahedra. The second-harmonic-generation signal intensities of the two sulfides and two selenides were close to those of AgGaS(2) and AgGaSe(2), respectively, when probed with a laser with 2090 nm as the fundamental wavelength. They possess large band gaps of 3.61(2) eV for Li(2)In(2)SiS(6), 3.45(2) eV for Li(2)In(2)GeS(6), 2.54(2) eV for Li(2)In(2)SiSe(6), and 2.30(2) eV for Li(2)In(2)GeSe(6), respectively. Moreover, these four compounds all melt congruently at relatively low temperatures, which makes it feasible to grow bulk crystals needed for practical application by the Bridgman-Stockbarger method.

LiGaGe2Se6: A New IR Nonlinear Optical Material with Low Melting Point

The new compound LiGaGe(2)Se(6) has been synthesized. It crystallizes in the orthorhombic space group Fdd2 with a = 12.501(3) Å, b = 23.683(5) Å, c = 7.1196(14) Å, and Z = 8. The structure is a three-dimensional framework composed of corner-sharing LiSe(4), GaSe(4), and GeSe(4) tetrahedra. The compound exhibits a powder second harmonic generation signal at 2 μm that is about half that of the benchmark material AgGaSe(2) and possesses a wide band gap of about 2.64(2) eV. LiGaGe(2)Se(6) melts congruently at a rather low temperature of 710 °C, which indicates that bulk crystals can be obtained by the Bridgman-Stockbarger technique. According to a first-principles calculation, there is strong hybridization of the 4s and 4p orbitals of Ga, Ge, and Se around the Fermi level. The calculated birefractive index is Δn = 0.04 for λ ≥ 1 μm, and the calculated major SHG tensor elements are d(15) = 18.6 pm/V and d(33) = 12.8 pm/V. This new material is promising for application in IR nonlinear optics.

Bi2(IO4)(IO3)3: A New Potential Infrared Nonlinear Optical Material Containing [IO4]3– Anion

A new potential infrared (IR) nonlinear optical (NLO) material Bi(2)(IO(4))(IO(3))(3) was synthesized by hydrothermal method. Bi(2)(IO(4))(IO(3))(3) crystallizes in the chiral orthorhombic space group P2(1)2(1)2(1) (No. 19) with a = 5.6831(11) Å, b = 12.394(3) Å, and c = 16.849(3) Å. It exhibits a three-dimensional framework through a combination of the IO(3), IO(4), BiO(8), and BiO(9) polyhedra and is the first noncentrosymmetric (NCS) structure containing [IO4](3-) anion. Bi(2)(IO(4))(IO(3))(3) has an IR cutoff wavelength of 12.3 μm and belongs to the type 1 phase-matchable class with a moderately large SHG response of 5 × KDP, which is in good agreement with the theoretical calculations.

Ultraviolet nonlinear optical crystal: CsBe 2 BO 3 F 2

A new ultraviolet nonlinear optical crystal CsBe2BO3F2 has been grown by the flux method with relatively greater size and thickness along the z axis. The crystal structure was determined by single-crystal x-ray diffraction analysis and the space group of it was defined as R32, belonging to the uniaxial class. Optical properties including the ultraviolet absorption edges, refractive indices, phase-matching angles, and effective nonlinear optical coefficients have been systematically determined for the first time. Based on the measured refractive indices, the Sellmeier equations were also fitted.

Trigonal Planar [HgSe3]4– Unit: A New Kind of Basic Functional Group in IR Nonlinear Optical Materials with Large Susceptibility and Physicochemical Stability

A new mercury selenide BaHgSe2 was synthesized. This air-stable compound displays a large nonlinear optical (NLO) response and melts congruently. The structure contains chains of corner-sharing [HgSe3](4-) anions in the form of trigonal planar units, which may serve as a new kind of basic functional group in IR NLO materials to confer large NLO susceptibilities and physicochemical stability. Such trigonal planar units may inspire a path to finding new classes of IR NLO materials of practical utility that are totally different from traditional chalcopyrite materials.

Ba2AgInS4 and Ba4MGa5Se12 (M = Ag, Li): syntheses, structures, and optical properties

The first two members in alkaline-earth/group XI/group XIII/chalcogen system, namely Ba(2)AgInS(4) and Ba(4)AgGa(5)Se(12), were synthesized along with a Li analogue Ba(4)LiGa(5)Se(12). Ba(2)AgInS(4) crystallizes in space group P2(1)/c. It contains [AgInS(4)](4-) layers built from AgS(3) triangles and InS(4) tetrahedra with Ba(2+) cations inserted between the layers. Ba(4)AgGa(5)Se(12) and Ba(4)LiGa(5)Se(12) adopt two closely-related structure types in space group P4[combining macron]2(1)c with structural difference originating from the different positions of Ag and Li in them. The three-dimensional framework in Ba(4)AgGa(5)Se(12) is composed of GaSe(4) tetrahedra with the Ba and Ag atoms occupying the large and small channels respectively, whereas that in Ba(4)LiGa(5)Se(12) is built from LiSe(4) and GaSe(4) tetrahedra with channels to accommodate the Ba atoms. As deduced from the diffuse reflectance spectra measurement, the optical band gaps were 2.32 (2) eV, 2.52 (2) eV, and 2.65 (2) eV for Ba(2)AgInS(4), Ba(4)AgGa(5)Se(12), and Ba(4)LiGa(5)Se(12), respectively.

Ba3LnInS6 (Ln = Pr, Sm, Gd, Yb) and Ba2LnGaS5 (Ln = Pr, Nd): syntheses, structures, and magnetic and optical properties.

Six new quaternary rare-earth sulfides Ba(3)LnInS(6) (Ln = Pr, Sm, Gd, Yb) and Ba(2)LnGaS(5) (Ln = Pr, Nd) have been synthesized for the first time. Ba(3)LnInS(6) (Ln = Pr, Sm, Gd, Yb) belong to the centrosymmetric space group R3[overline]c of the trigonal system. The structures contain infinite one-dimensional anionic chains (1)(∞)[LnInS(6)](6-), which are built from face-sharing LnS(6) distorted triangular prisms and InS(6) octahedra. Ba(2)LnGaS(5) (Ln = Pr, Nd) crystallize in the centrosymmetric space group I4/mcm of the tetragonal system. Their structures consist of (BaLn)S layers built from (BaLn)S(8) bicapped trigonal prisms. These layers are stacked perpendicular to the c axis and further connected by GaS(4) tetrahedra to form a three-dimensional framework with channels occupied by Ba(2+) cations. As deduced from magnetic susceptibility measurements on Ba(2)NdGaS(5), it is paramagnetic and obeys the Curie-Weiss law. Besides, the band gap of Ba(2)NdGaS(5) is determined to be about 2.12(2) eV.