SHG Materials SnGa4Q7 (Q = S, Se) Appearing with Large

Article pubs.acs.org/cm

SHG Materials SnGa4Q7 (Q = S, Se) Appearing with Large Conversion Efficiencies, High Damage Thresholds, and Wide Transparencies in the Mid-Infrared Region Zhong-Zhen Luo,†,‡ Chen-Sheng Lin,† Hong-Hua Cui,†,‡ Wei-Long Zhang,† Hao Zhang,† Zhang-Zhen He,† and Wen-Dan Cheng*,† †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, P. R. China ‡ University of Chinese Academy of Sciences, Beijing 100039, P. R. China S Supporting Information *

ABSTRACT: Two new ternary noncentrosymmetric (NCS) isostructural compounds, SnGa4S7 (1) and SnGa4Se7 (2), have been synthesized by a high-temperature solid-state reaction method. Both compounds crystallize in the monoclinic polar space group Pc (7), and their three-dimensional (3D) frameworks are assembled from [SnQ4] tetragonal pyramids and tetranuclear [Ga4Q11] units. The two crystals show large second harmonic generation (SHG) conversion efficiencies, high laser-induced damage thresholds (LIDTs), and wide transparent regions in the mid-infrared (MIR) zone. Compound 2 exhibits the largest SHG conversion efficiency among type-I phase-matchable chalcogenides of about 3.8 × AgGaS2 at 2.05 μm radiation and a high LIDT of 4.6 × AgGaS2. Theoretical studies elucidate that the stereochemically active lone-pair (SCALP) electrons of Sn2+ can significantly improve the polarity of the [SnQ4] unit. Large nonlinear optical (NLO) responses for 1 and 2 originate from the covalent interactions of Sn−Q and the cooperative effects of polarities between the units [SnQ4] and [GaQ4]. Additionally, their comparatively simple chemical composition and high chemical stability give them promise for practical applications.

■

SHG coefficient decreases with an increase in the band gap.9,10 Thus, it is difficult to discover or design new NLO materials having both large band gaps and strong SHG responses in the region of interest. As a consequence, the exploration for new high-quality MIR NLO crystals is an urgent task with respect to science and technology at present. Recently, some developments have been made in MIR NLO crystals.11 BaGa4S7 and BaGa4Se7, for example, exhibit large NLO coefficients with d33 = 12.6 and 20.6 pm/V and band gaps of 3.54 and 2.64 eV, respectively. These NLO responses originate from distorted tetrahedra [GaS4]/[GaSe4].12,13 It has been reported that the divalent Sn(II) atom can adopt several types of noncentrosymmetric (NCS) chromophores, including SnS3 trigonal pyramids, Sn2S3 trigonal bipyramids, and SnS4 tetragonal pyramids.14 In the design of NLO compounds, two or more types of NCS chromophores are usually employed to improve the possibility of forming an NCS crystal.11f Among these NCS chromophores, the NLO active units possessing

INTRODUCTION Second-order NLO crystals are playing an increasingly important role in modern coherent laser generation and optical parameter oscillator (OPO) processes, such as parametric generation of tunable lights. These laser sources are applied to noninvasive medical diagnostics, long-distance and highcapacity communication networks, optoelectronic storage devices, environmental monitoring, laser guidance, deep-space detectors, etc.1−4 Over the past decades, numerous outstanding NLO crystals have been discovered and extensively studied including BaB2O4 (BBO), LiB3O5 (LBO), KH2PO4 (KDP), KTiOPO4 (KTP), and LiNbO3 (LNO),5 which are satisfactory for actual applications in the UV and visible regions. In contrast, only a few NLO crystals (e.g., AgGaQ2 (Q = S, Se), and ZnGeP2) are commercially available in the MIR region of 2−25 μm, which is called the fingerprint region for organic and inorganic molecules and covers two important atmospheric transparent windows (3−5 and 8−14 μm).6,7 However, these crystals suffer serious disadvantages that limit their applications, such as low LIDT, nonphase-matchable at 1 μm, and strong two-photon absorption.8 It is well-known that high LIDT usually corresponds to a large energy band gap; instead, the © 2014 American Chemical Society

Received: February 26, 2014 Revised: March 20, 2014 Published: March 21, 2014 2743

dx.doi.org/10.1021/cm5006955 | Chem. Mater. 2014, 26, 2743−2749

Chemistry of Materials

Article

stereochemically active lone-pair (SCALP) electrons always play an important role in the NLO response.15 Inspired by these ideas, we have exploited the Sn(II)/Ga/Q (Q = S, Se) systems for new NCS compounds, and two NCS compounds, SnGa4S7 (1) and SnGa4Se7 (2), have been obtained for the first time in our laboratory. Remarkably, both of them show large SHG conversion efficiencies, high damage thresholds, wide transparent regions in the MIR zone, and good optical performances.

■

Table 1. Crystal Data and Structural Refinement Details for 1 and 2

EXPRIMENTAL SECTION

Syntheses. All reagents in these synthetic studies were used as obtained: Sn (5N, Sinopharm Chemical Reagent Company, Ltd.); Ga (5N, Sinopharm Chemical Reagent Company, Ltd.); S (99.999%, Sinopharm Chemical Reagent Co., Ltd.); Se (higher than 99.9%, Alfa Aesar China Co., Ltd.). All reactants were mixed roughly and loaded into a graphite crucible sealed in an evacuated silica tube, which was then placed and heated in a computer-controlled resistance furnace. SnGa4S7 (1). A stoichiometric mixture of Sn (95.4 mg, 0.80 mmol), Ga (224.2 mg, 3.22 mmol), and S (180.4 mg, 5.63 mmol) was loaded into a silica tube, which was sealed under vacuum. The mixture was heated to 1123 K within 48 h, kept at this temperature for 96 h, and cooled to 673 K in 100 h, followed by cooling to room temperature in 24 h. Light-yellow crystals were obtained, which were stable in air for months. SnGa4Se7 (2). Compound 2 was obtained by the same procedure as for 1, except that Sn (153.8 mg, 1.29 mmol), Ga (90.4 mg, 1.29 mmol), and Se (255.8 mg, 3.24 mmol) were used. Consequently, yellow crystals that were stable in air for months were obtained after cooling to room temperature. X-ray Crystallography. Suitable single crystals of 1 and 2 were selected and mounted on glass fibers for single-crystal X-ray diffraction (XRD) analysis. The measurements of single-crystal XRD data were performed on a Mercury70 diffractometer equipped with a graphitemonochromated Mo Kα radiation source (λ = 0.71073 Å) at 293 K. The data were collected with a ω-scan technique and corrected for Lorentz and polarization factors. The multiscan method was used to the absorption corrections.16 The crystal structures of the two compounds were solved by direct methods and refined by full matrix least-squares on F2 using SHELXL-97 with anisotropic thermal parameters for all atoms.17 All sites were fully occupied in the structures. The refined structures were checked by using the ADDSYM algorithm in the program PLATON to make sure that there were no missed or higher symmetry elements.18 Crystallographic data and structural refinements information are given in Table 1. The atomic coordinates, equivalent isotropic thermal parameters, and important bond distances and angles for compounds are listed in Tables S1 and S2 in Supporting Information. ICSD nos. 427018 and 427019 contain the supplementary crystallographic data for this work. The data can be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: (49) 7247-808-666; e-mail: crysdata@fiz-karlsruhe.de). Elemental Analysis. The elemental analyses of the compounds were performed with the aid of a field emission scanning electron microscope (FESEM, JSM6700F) equipped with an energy-dispersive X-ray spectroscope (EDX, Oxford INCA). The presence of Sn, Ga, Se, and S has been examined and is shown in Figure S2 in Supporting Information, based on this semiquantitative microprobe analyses method by only checking the surfaces of the samples. Powder X-ray Diffraction. The powder X-ray diffraction patterns (PXRD) of the ground powder of 1 and 2 were collected on a Rigaku MiniFlex II diffractometer (Cu Kα radiation, λ = 1.5406 Å). The 2θ range is 5−85°, with a step size of 0.02° and a scan speed of 0.3°/min. PXRD patterns are in good agreement with the simulated patterns generated using the CIF of each refined structure (Figure S3, Supporting Information). Infrared and Solid-State UV−vis−NIR Diffuse Reflectance Spectra. The infrared spectra of 1 and 2 were measured by using a PerkinElmer Spectrum One FR-IR spectrometer in the range of 400−

chemical formula

SnGa4S7 (1)

SnGa4Se7 (2)

formula weight space group a (Å) b (Å) c (Å) β (deg) V (Å3), Z ρcal (g cm−3) absorption correction μ (mm−1) crystal size (mm) F(000) R1,a wR2,b for I > 2σ(I) R1,a wR2,b for all data GOF on F2

622.08 Pc 7.269(5) 6.361(4) 12.408(8) 106.556(11) 549.9(6), 2 3.757 multiscan 13.178 0.19 × 0.17 × 0.16 572 0.0196, 0.0418 0.0203, 0.0419 0.979

950.31 Pc 7.577(4) 6.666(3) 13.023(8) 106.680(7) 630.1(6), 2 5.009 multiscan 30.560 0.10 × 0.10 × 0.08 824 0.0489, 0.1099 0.0562, 0.1158 1.032

R1 = ∑∥Fo| − |Fc∥/∑|Fo|. ∑w(Fo2)2]1/2.

a

b

wR2(Fo2) = [∑w(Fo2 − Fc2)2/

4000 cm−1 at room temperature. Powder samples and dry KBr were mixed and ground into fine powder, which was then pressed into transparent sheets for the measurement. The UV−vis diffuse reflectance spectra were recorded at room temperature using a PerkinElmer Lambda 900 UV−vis spectrometer in the range of 200−2500 nm. The BaSO4 standard white board was used as a 100% reflectance comparison standard. The reflectance spectroscopy versus wavelength data were converted from diffuse reflectance spectra according to the Kubelka−Munk function: α/S = (1 − R)2/2R, where R is the reflectance coefficient, and α and S are the absorption and scattering coefficient, respectively.19 Second Harmonic Generation (SHG) Measurements. The SHG measurement for both compounds was carried out by using the Kurtz and Perry method using laser radiation wavelength of 2050 nm.20 Powder samples of 1 and 2 were ground and sieved into several distinct particle size ranges of 25−45, 45−74, 74−106, 106−150, and 150−210 μm, and then pressed into disks, respectively, with a diameter of 8 mm. Powdered AgGaS2 was prepared with the same size range as the reference. The SHG intensity can be derived from the amplitudes of the two interacting electric fields 2 I2ω = (512π 5/c)(deff /n(2ω)n(ω)2 )(Iω2 L2/λω2)

[sin(Δkl /2)/(Δkl /2)]2

(1)

while phase-matching, i.e., Δk → 0. The figure of merit (FOM) is defined as FOM = d2eff/n(2ω)n(ω)2, and then we have

I2ω = (512π 5/c)FOM(Iω2 L2/λω2)

(2)

The SHG conversion efficiency is defined as η = I2ω/Iω. Accordingly, we can derive the relative SHG conversion efficiencies ηS/ηR = (IS2ω/ Iω)/(IR2ω/Iω) from the relative SHG intensities IS2ω/IR2ω between sample and reference. Furthermore, the NLO coefficient of the sample can be estimated from dSeff ≈ (IS2ω/IR2ω)1/2dReff when omitting the differences in refractive n between the sample and reference. Powder Laser-Induced Damage Threshold Measurements (LIDT). To evaluate the powder LIDTs of 1 and 2, the single pulse measurement method was used with AgGaS2 as the reference.21 The same particle size samples (150−210 μm) of 1, 2, and AgGaS2 were packaged into disks in 1-mm-thick plastic holders with a diameter of 8 mm. The optical microscope was used to observe the changes of the compounds when high-power 1064 nm laser radiation passed with a pulse width τp of 8 ns. A vernier caliper and a Nova II sensor with a PE50-DIF-C energy sensor were employed in the measurement of the damage spots and the power of laser beam, respectively. 2744



Article

Thermal Analyses. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were all carried out with a NETZSCH STA 449C thermal analyzer. A powder sample of about 15 mg and the reference (Al2O3) were enclosed in a platinum crucible and then heated from 40 °C to 800 °C at 10 °C/min under N2 flow at a rate of 30 mL/min. Results of TGA and DTA measurements indicate that the compounds are thermally stable up to 700 °C for 1 and 600 °C for 2 under a N2 atmosphere (Figure S4, Supporting Information). Electronic Structure Calculations. The calculations of energy band structure and nonlinear optical properties were accomplished by using the first principles plane-wave pseudopotential method with the CASTEP code provided by the Material Studio package.22,23 Interaction of the electrons with ion cores was represented by norm-conserving pseudopotentials,24,25 and the valence electronic configuration for the component element was Sn 5s25p2, Ga 3d104s24p1, Se 4s24p4, and S 3s23p4. Local-density approximation (LDA) with an cutoff energy and precision of 590 eV and 2.0 × 10−6 eV/atom were employed. A Monkhorst−Pack scheme26 k-point grid density of 2 × 2 × 1 was used for 1 and 2 in the first Brillouin zone of the unit cell. SHG Coefficient Calculations. The SHG coefficients are calculated by using the “velocity-gauge” formula derived by Sipe et al.: χ (2) (− 2ω ; ω , ω) =

i e 2 mω

∑∫ i ,j,l

BZ

Figure 1. (a) The structure of 1 viewed along the a axis. Red, turquiose, and yellow balls represent Sn, Ga, and S atoms, respectively. (b) The structure of the tetranuclear [Ga4S11] unit in the red circle viewed down the c axis.

2.463(3) Å in 2, which are close to those of Ga−S (2.228 to 2.338 Å) in BaGa4S7 and Ga−Se (2.362 to 2.488 Å) in BaGa4Se7, respectively.12,13 Four tetrahedra [GaQ4] form the tetranuclear [Ga 4 Q 11 ] unit, in which the [Ga(1)Q 4 ], [Ga(2)Q4] and [Ga(4)Q4], tetrahedra connect to each other via Q(7), Q(2), and Q(5), respectively (Figure 2).

3

f jl ⎤ dk pij pjl plj ⎡⎢ fil ⎥ + E − Ejl ⎥⎦ 4π 3 2E − Eji ⎢⎣ E − Eli (3)

In this formula, the optical transition dipole moment p is taken from dielectric function of CASTEP optical properties calculation. In this manner, we calculated the imaginary part of χ(2)′, and the real part of χ(2)″ was obtained by Kramers−Kronig Relations on the imaginary part. The total second-order susceptibility χ(2) = (|χ(2)′|2 + |χ(2)″|2)1/2 and d = 2χ(2). Calculations of Group Dipole Moments and Electron Localization Function (ELF). The dipole moments of (SnSe4)6− were calculated by the Guassian 03 program.27 The geometry was taken from the unit cell of the experimental X-ray crystal structure without further optimization, and the original point was set to be at the Sn2+ position. The basis set was 6-31+G* for Se atoms, and LANL2DZ for the Sn atom. The ELF was obtained by the VASP program.28

Figure 2. The tetranuclear [Ga4Q11] unit of the title compounds. Turquiose and yellow balls represent Ga and Q atoms, respectively.

■

Optical Properties. Diffuse-reflectance UV−vis/near-IR spectra reveal band gaps of 3.10 (400 nm) and 2.55 eV (486 nm) for 1 and 2 (Figure 3), respectively. The crystal colors are light-yellow and yellow (590 to 560 nm) (Figure S1, Supporting Information), which are below the band gaps. This is due to the energy loss during the photon emission processes that appears as phonon or lattice vibrations for indirect band gap materials (see subsection Theoretical Analyses of the Optical Properties). No obvious optical absorption peaks are observed in the IR transmission spectra of 1 and 2 as shown in Figure 3. Thus, both compounds have wide transparent regions, from 0.40 to 25 μm for 1 and 0.49 to 25 μm for 2, respectively, covering the two important atmospheric transparent windows (3−5 and 8−14 μm).7 NLO Properties. The SHG intensities of 1 and 2 have been investigated using the Kurtz and Perry method with a 2.05 μm laser. The ternary chalcopyrite AgGaS2 with noncentrosymmetric crystal class −42m has been widely used as benchmark material for decades, due to good properties, such as high SHG coefficient (d36) (13.7 pm/V), wide transparent region (0.5−17 μm), relatively large birefringence, and easy availability.6,31 As shown in Figure 4, the SHG intensities of the two compounds increase with the increase in particle size, which indicates that

RESULTS AND DISCUSSION Crystal Structure Description. Compounds 1 and 2 crystallize in Pc (7) of the monoclinic system, with the unit cell parameters (1/2) a = 7.269(5)/7.577(4) Å, b = 6.361(4)/ 6.666(3) Å, c = 12.408(8)/13.023(8) Å, β = 106.556(11)/ 106.680(7), and Z = 2. The remarkable structures of the 3D frameworks were formed by the tetranuclear secondary basic structure unit [Ga4Q11], which was constructed with four [GaQ4] tetrahedra with [SnQ4] tetragonal pyramids locating in the cavities (Figure 1). There are one crystallographically Sn atom, four different Ga atoms, and seven unique Q atoms in an asymmetric unit. As shown in Figure 1a and 1b, the Sn atom is bonded to four Q atoms at two short and two long distances, forming the [SnQ4] tetragonal pyramid, which are antiparallel in interlayer and parallel in intralayer along the b axis, respectively. The Sn−Q bond distances range from 2.654(19) to 2.992(17) Å in 1 and 2.773(2) to 3.111(2) Å in 2, which are comparable with those of Sn−S (2.659 to 3.102 Å) in Sn2S3 and Sn−Se (2.714(3) to 3.454(2) Å) in Ba3Bi6SnSe13, respectively.29,30 All four Ga sites are coordinated to the tetrahedra [GaQ4] by four Q atoms. The Ga−Q bond lengths range from 2.214(2) to 2.337(16) Å in 1 and 2.346(3) to 2745



Article

Figure 5. Oscilloscope traces of SHG signals for 1 and 2 with AgGaS2 as a reference at a particle size of 150−210 μm.

tetragonal pyramid structure. In other words, the cooperative effects of two or more NCS chromophores can lead to a strong SHG response.15a Thus, taking advantage of two or more types of NCS chromophores is a good design approach to obtain an outstanding NLO material. Powder Laser-Induced Damage Threshold Measurements (LIDT). The results of powder LIDTs using single pulse measurement for 1, 2, and AgGaS2 (as a reference) are summarized in Table 2. Small spot diameters (3.1 mm for 1

Figure 3. Reflection spectra, UV−vis diffuse reflectance spectra (inset panel), and IR spectra of 1 (a) and 2 (b).

Table 2. Results of Powder LIDT Measurement for 1, 2, and AgGaS2 compounds

damage energy (mJ)

spot diameter (mm)

damage threshold (MW/cm2)

AgGaS2 SnGa4S7 SnGa4Se7

12.13 49.83 34.00

6.7 3.1 5.2

8.6 165.1 40.0

and 5.2 mm for 2) are selected in this measurement, because the damage energies of 1 (49.83 mJ) and 2 (34.00 mJ) are much larger than that of AgGaS2 (12.13 mJ). The LIDTs of 1 (165.1 MW/cm2) and 2 (40.0 MW/cm2) are about 19 and 4.6 times that of AgGaS2 (8.6 MW/cm2), respectively, as shown in Table 2. These high LIDTs imply that 1 and 2 are promising for high-power NLO application in the IR region. Theoretical Analyses of the Optical Properties. Band structures of 1 and 2 were calculated by the density functional theory (DFT) as shown in Figure 6. The lowest unoccupied conduction band (CB) and the highest occupied valence band (VB) of 1 as well as 2 are located at G and B k-points, respectively. The calculated results give indirect band gaps of 2.28 eV for 1 and 1.87 eV for 2, which are underestimated compared with the experimental results. Additionally, the HSE06 (Heyd−Scuseria−Ernzerhof) hybrid functional32 was applied as implemented in VASP, to calculate the band gaps of the two compounds. It gives band gaps of 3.242 and 2.588 eV for 1 and 2, respectively, which agree well with the experimental results. In Figure 7a, the top of the VB (near the Fermi level) mainly contains S-3p, Sn-5s/-5p states mixing with a small part of Ga-4s/-4p states for 1. The bottom of the CB is composed of S-3p, Ga-4s/-4p, and Sn-5p states with some mixtures of the Sn-5s state. Accordingly, the optical response of 1 originates from the electronic transitions from the

Figure 4. Phase-matching curves, i.e., particle size vs SHG response for 1 and 2 with AgGaS2 as a reference.

both 1 and 2 achieve the type-I phase-matching. This finding (type-I phase-matching) implies that the polarization of both input beams at ω frequencies are parallel to each other, and the polarization of the output beam at 2ω is orthogonal to the input beams. The SHG intensity of 1 is about 1.3 times that of the benchmark AgGaS2 at a particle size of 150−210 μm. More encouragingly, compound 2 exhibits the strongest SHG response among type-I phase-matching chalcogenides, which is approximately 3.8 times that of the benchmark AgGaS2 at a particle size of 150−210 μm (Figure 5). In fact, Figure 4 also indicates the SHG conversion efficiencies, ηSGS/ηAGS = 1.3 and ηSGE/ηAGS = 3.8, i.e., the conversion efficiencies of 1 and 2 are 1.3 and 3.8 times larger than those of AgGaS2, separately, with the same experimental conditions and devices. Furthermore, the SHG coefficients deff of 1 and 2 are estimated to be 15.62 and 26.71 pm/V with AgGaS2 (dReff = 13.7 pm/V) as a reference, respectively (dSeff ≈ (IS2ω/IR2ω)1/2dReff). Compared with the results of BaGa4Q7 only containing the distorted [GaQ 4 ] tetrahedron, the SHG responses of the title compounds are evidently boosted by the [SnQ4] unit with 2746



Article

Figure 7. TDOS and PDOS of 1 (a) and 2 (b).

Figure 6. Calculated band structures of 1 (a) and 2 (b).

Ga−S and Sn−S bonding states to their antibonding states. The DOS of 2 is similar to that of 1, except that the Se-4s state makes more contribution in the CB. Therefore, the optical response of 2 results from the Sn−Se and Ga−Se bonding states to their antibonding states. Interestingly, the dominant contribution of the Sn-5s state in 1 and 2 is found at the lower energy range of −7.5 to −5.0 eV rather than at the top of the VB from PDOS of Sn (Figure 7). The indirect mixture between Sn-5s and Sn-5p states is mediated by hybridization with S-3p or Se-4p states at the top of the VB. Moreover, the hybridized states of Sn-5s with S-3p or Se-4p close to the Fermi level account for only a small fraction of the total Sn-5s states. These findings show that the formation of the Sn2+ 5s2 lone-pair electrons depends on the S2‑ or Se2‑ anion, and this dependence on the electronic states of the anion can be evidence of SCALP electrons.33 Another indication of the SCALP electrons can be found from the electron localization function (ELF) map. A two-dimensional ELF slice ((001) plane) of 2 containing Sn and Se atoms has been plotted in Figure 8. A nonspherical symmetric density distribution (s-orbital spherical distribution) is clearly presented around each Sn atom, and the bond axis electronic distributions connecting with its nearest-neighboring Se atom (Sn−Se covalence interactions) appear. The local dipole moments created from the SCALP electron in the [SnSe4] group are in parallel alignment (x and z direction), and the cooperative effects of all local dipoles result in the enhancement of the macroscopic dipole moments of the

Figure 8. The ELF map of 2 at (001) plane cutting through the Sn and Ga atoms and the ELF value ranging from 0 (blue) to 1 (red).

compound. The calculated results suggest the enhancement of the moments at x and z directions (Table 4). The above discussions indicate that the covalent interaction of Sn−Q and the cooperative effects of polarities among [SnQ4]6− and [GaQ4]5− lead to large NLO responses together in compounds SnGa4Q7, as compared with those of BaGa4Q7 only containing distorted GaQ4 tetrahedra.12,13 Simultaneously, the important Table 3. Theoretically Determined SHG Coefficients (pm/ V) of 1 and 2 at a Wavelength of 2.05 μm (0.60 eV)

2747

compounds

d11

d12

d13

d15

d24

d33

SnGa4S7 SnGa4Se7

−6.82 −4.82

−2.39 −1.77

−3.54 −5.54

9.12 18.84

−10.19 −13.80

15.70 37.51



■

Table 4. Calculated Dipole Moments (Debye) of [SnSe4]6− Localized at Different Layers in Compound 2 group 6−

[SnSe4] (1) [SnSe4]6− (2)

x

y

z

absolute total value

0.030 0.030

−32.981 32.981

−1.075 −1.075

32.998 32.998

ASSOCIATED CONTENT

S Supporting Information *

Experimental and theoretical methods, X-ray diffraction patterns, X-ray crystallographic files in CIF format, and additional tables and figures for 1 and 2 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

properties of SnGa4Q7 and BaGa4Q7 are listed in Table 5 for comparison. The space groups of 1 and 2 both belong to class m, and there are ten nonvanishing tensors (d11, d12, d13, d15, d24, d26, d31, d32, d33, and d35) of second-order susceptibility. Judging from Kleinman’s symmetry, only six independent tensor components (d11, d12, d13, d15, d24, and d33) are taken into account. Theoretical values for the SHG coefficients are calculated by using the “velocity-gauge” formula derived by Sipe et al and shown in Table 3.34 The largest tensor components (d33) of 1 and 2 are calculated to be 15.70 and 37.51 pm/V at a wavelength of 2.05 μm (0.60 eV), respectively.

■

Article

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This investigation was based on work supported by the National Basic Research Program of China (grant no. 2014CB845605), the National Natural Science Foundation of China under projects 21173225, 91222204, and 21101156, and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry. We thank Prof. Ning Ye and Dr. Guohong Zou at FJIRSM for help with the SHG measurements and Prof. Ge Zhang and M. E. Bingxuan Li at FJIRSM for help with the LIDT measurements.

CONCLUSIONS

■

In summary, two new ternary chalcogenides, SnGa4S7 (1) and SnGa4Se7 (2), have been synthesized and characterized. Their structures are constructed with [SnQ4] tetragonal pyramids and tetranuclear secondary basic structure units [Ga4Q11] aggregated by four [GaQ4] tetrahedra. The SHG intensity of 1 is about 1.3 times that of AgGaS2, and remarkably, compound 2 exhibits the strongest SHG response among type-I phasematching chalcogenides to date, which is approximately 3.8 times that of the benchmark AgGaS2 at a particle size of 150− 210 μm. Furthermore, the conversion efficiencies of 1 and 2 are 1.3 and 3.8 times that of AgGaS2 with the same experimental conditions and devices, respectively. Moreover, the two compounds have high powder LIDTs (19 and 4.6 times that of AgGaS2 for 1 and 2, respectively) and wide IR transparent regions extending to more than 25 μm. Studies of the microcopy mechanism show that the SCALP electrons of Sn2+ can significantly improve the polarity of the [SnQ4] unit. The cooperative effects of the [SnQ4] and [GaQ4] polarities, and the covalent interaction of Sn−Q, lead to strong NLO responses and good optical performances. The two crystals present the chemical characteristics of simple and environmentally friendly ingredients and high stability. More importantly, they show the physical characteristics of large SHG conversion efficiencies, type-I phase-matchablility, high damage thresholds, and wide IR transparent regions. Accordingly, we expect 1 and 2 to have significant applications in infrared laser devices with adjustable frequency.

REFERENCES

(1) (a) Shunemann, C. P. Proc. SPIE-Int. Soc. Opt. Eng. 2007, 6455, 64550R-1. (b) Hazama, H.; Takatani, Y.; Awazu, K. Proc. SPIE-Int. Soc. Opt. Eng. 2007, 6455, 645507-1. (2) (a) Gmachl, C.; Capasso, F.; Kohler, R.; Tredicucci, A.; Hutchinson, A. L.; Sivco, D. L.; Baillargeon, J. N.; Cho, A. Y. IEEE Circuits Devices 2000, 16, 10−18. (b) Capasso, F.; Paiella, R.; Martini, R.; Colombelli, R.; Gmachl, C.; Myers, T. L.; Taubman, M. S.; Williams, R. M.; Bethea, C. G.; Unterrainer, K.; Hwang, H. Y.; Sivco, D. L.; Cho, A. Y.; Sergent, A. M.; Liu, H. C.; Whittaker, E. A. IEEE J. Quantum Electron. 2002, 38, 511−532. (3) (a) Bera, T. K.; Jang, J. I.; Ketterson, J. B.; Kanatzidis, M. G. J. Am. Chem. Soc. 2009, 131, 75. (b) Zhang, Q.; Chung, I.; Jang, J. I.; Ketterson, J. B.; Kanatzidis, M. G. J. Am. Chem. Soc. 2009, 131, 9896. (c) Banerjee, S.; Malliakas, C. D.; Jang, J. I.; Ketterson, J. B.; Kanatzidis, M. G. J. Am. Chem. Soc. 2008, 130, 12270. (4) Cotter, D.; Manning, R. J.; Blow, K. J.; Ellis, A. D.; Kelly, A. E.; Nesset, D.; Phillips, I. D.; Poustie, A. J.; Rogers, D. C. Science 1999, 286, 1523−1528. (5) (a) Bordui, P. F.; Fejer, M. M. Annu. Rev. Mater. Sci. 1993, 23, 321−379. (b) Nikogosyan, D. N. Nonlinear optical crystals: A complete survey, 1st ed.; Springer: New York, 2005. (6) (a) Harasaki, A.; Kato, K. Jpn. J. Appl. Phys. 1997, 36, 700. (b) Tell, B.; Kasper, H. M. Phys. Rev. B 1971, 4, 4455. (c) Boyd, G. D.; Buehler, E.; Storz, F. G. Appl. Phys. Lett. 1971, 18, 301. (7) (a) Dmitriev, V. G.; Gurzadyan, G. G.; Nikogosyan, D. N. Handbook of Nonlinear Optical Crystals; Springer: New York, 1999. (b) Ebrahim-Zadeh, M.; Sorokina, I. T. Mid-Infrared Coherent Sources and Applications; NATO Science for Peace and Security Series B: Physics and Biophysics; Springer: New York, 2007.

Table 5. Important Properties of SnGa4Q7 and BaGa4Q7 SnGa4S7 relative SHG intensities band gaps (eV) transparent regions (μm) LIDTs largest tensors (pm/V) a

1.3 × AGS 3.10 0.40−25 19 × AGS 15.70

a

SnGa4Se7

BaGa4S7

BaGa4Se7

3.8 × AGS 2.55 0.49−25 4.6 × AGS 37.51

∼AGS 3.54 0.35−13.7 4 × AGS 12.6

2−3 × AGS 2.64 0.47−18 3.7 × AGS −20.6

AGS = AgGaS2. 2748



Article

(8) (a) Jayaraman, A.; Narayanamurti, V.; Kasper, H. M.; Chin, M. A.; Maines, R. G. Phys. Rev. B 1976, 14, 3516. (b) Schunemann, P. G. AIP Conf. Proc. 2007, 916, 541−559. (9) Wu, K. C.; Chen, K. C. Appl. Phys. A: Mater. Sci. Process. 1992, 54, 209−220. (10) Chen, C.; Lin, Z.; Wang, Z. Appl. Phys. B: Lasers Opt. 2005, 80, 1−25. (11) (a) Ding, N.; Kanatzidis, M. G. Angew. Chem., Int. Ed. 2006, 45, 1397−1401. (b) Manos, M. J.; Chrissafis, K.; Kanatzidis, M. G. J. Am. Chem. Soc. 2006, 128, 8875−8883. (c) Morris, C. D.; Chung, I.; Park, S.; Harrison, C. M.; Clark, D. J.; Jang, J. I.; Kanatzidis, M. G. J. Am. Chem. Soc. 2012, 134, 20733−20744. (d) Lekse, J. W.; Moreau, M. A.; McNerny, K. L.; Yeon, J.; Halasyamani, P. S.; Aitken, J. A. Inorg. Chem. 2009, 48, 7516−7518. (e) Reshak, A. H.; Kogut, Y. M.; Fedorchuk, A. O.; Zamuruyeva, O. V.; Myronchuk, G. L.; Parasyuk, O. V.; Kamarudin, H.; Auluck, S.; Plucinski, K. J.; Bila, J. Phys. Chem. Chem. Phys. 2013, 15, 18979−18986. (f) Chung, I.; Kanatzidis, M. G. Chem. Mater. 2014, 26, 849−869. (12) Lin, X. S.; Zhang, G.; Ye, N. Cryst. Growth Des. 2009, 9, 1186− 1189. (13) (a) Yao, J. Y.; Mei, D. J.; Bai, L.; Lin, Z. S.; Yin, W. L.; Fu, P. Z.; Wu, Y. C. Inorg. Chem. 2010, 49, 9212−9216. (b) Yao, J. Y.; Yin, W. L.; Feng, K.; Li, X. M.; Mei, D. J.; Lu, Q. M.; Ni, Y. B.; Zhang, Z. W.; Hu, Z. G.; Wu, Y. C. J. Cryst. Growth 2012, 364, 1−4. (14) (a) Luo, Z. Z.; Lin, C. S.; Zhang, W. L.; Zhang, H.; He, Z. Z.; Cheng, W. D. Chem. Mater. 2014, 26, 1093−1099. (b) Luo, Z. Z.; Lin, C. S.; Cheng, W. D.; Zhang, H.; Zhang, W. L.; He, Z. Z. Inorg. Chem. 2013, 52, 273−279. (c) Feng, K.; Jiang, X. X.; Kang, L.; Yin, W. L.; Hao, W. Y.; Lin, Z. S.; Yao, J. Y.; Wu, Y. C.; Chen, C. T. Dalton Trans. 2013, 42, 13635−13641. (15) (a) Zhang, W. L.; Cheng, W. D.; Zhang, H.; Geng, L.; Lin, C. S.; He, Z. Z. J. Am. Chem. Soc. 2010, 132, 1508−1509. (b) Nguyen, S. D.; Yeon, J.; Kim, S. H.; Halasyamani, P. S. J. Am. Chem. Soc. 2011, 133, 12422−12425. (c) Li, F.; Hou, X. L.; Pan, S. L.; Wang, X. Chem. Mater. 2009, 21, 2846−2850. (16) CrystalClear, version 1.3.5; Rigaku/MSC, Inc., Woodlands, TX, 1999. (17) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Solution; University of Göttingen, Göttingen, Germany, 1997. (18) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (19) Kortüm, G. Reflectance Spectroscopy; Springer-Verlag: New York, 1969. (20) Hervieu, M.; Perez, G.; Hagenmuller, P. Bull. Soc. Chim. Fr. 1967, 6, 2189−2194. (21) Zhang, M. J.; Jiang, X. M.; Zhou, L. J.; Guo, G. C. J. Mater. Chem. C 2013, 1, 4754−4760. (22) Payne, M. C.; Teter, M. P.; Allan, D. C.; Arias, T. A.; Joannopoulos, J. D. Rev. Mod. Phys. 1992, 64, 1045−1097. (23) Clark, S. J.; Segall, M. D.; Pickard, C. J.; Hasnip, P. J.; Probert, M. I. J.; Refson, K.; Payne, M. C. Z. Kristallogr. 2005, 220, 567−570. (24) Rappe, A. M.; Rabe, K. M.; Kaxiras, E.; Joannopoulos, J. D. Phys. Rev. B 1990, 41, 1227−1230. (25) Lin, J. S.; Qtseish, A.; Payne, M. C.; Heine, V. Phys. Rev. B 1993, 47, 4174−4180. (26) Dudarev, S. L.; Botton, G. A.; Savrasov, S. Y. C.; Humphreys, J.; Sutton, A. P. Phys. Rev. B 1998, 57, 1505. (27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,; X.; Knox, J. E. H. H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A. S. P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;

Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B; Gaussian Inc., Pittsburgh, PA, 2003. (28) Kresse, G.; Furthmüller, J. Comput. Mater. Sci. 1996, 6, 15. (29) Cruz, M.; Morales, J.; Espinos, J. P.; Sanzc, J. J. Solid State Chem. 2003, 175, 359−365. (30) Wang, Y. C.; DiSalvo, F. J. Chem. Mater. 2000, 12, 1011−1017. (31) (a) Nikogosyan, D. N. Nonlinear optical crystals: A complete survey, 1st ed.; Springer: New York, 2005. (b) Zondy, J. J.; Touahri, D.; Acef, O. J. Opt. Soc. Am. B 1997, 14, 2841−2497. (32) Heyd, J.; Scuseria, G. E.; Ernzerhof, M. J. Chem. Phys. 2003, 118, 8207. (33) (a) Payne, D. J.; Egdell, R. G.; Walsh, A.; Watson, G. W.; Guo, J.; Glans, P. A.; Learmonth, T.; Smith, K. E. Phys. Rev. Lett. 2006, 96, 157403−157406. (b) Yang, J.; Dolg, M. Phys. Chem. Chem. Phys. 2007, 9, 2094−2102. (34) Ghahramani, E.; Sipe, J. E. Phys. Rev. B 1991, 43, 8990−9002.

2749


SHG Materials SnGa4Q7 (Q = S, Se) Appearing with Large

Recommend Documents