A New KBBF-Family Nonlinear Optical Material with Strong InterlayerBondingYaoguo Shen,†,§,∥ Sangen Zhao,*,† Yi Yang,‡,§ Liling Cao,† Zujian Wang,† Bingqing Zhao,† Zhihua Sun,†

Zheshuai Lin,*,‡,§ and Junhua Luo*,†

†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,Fuzhou, Fujian 350002, China‡Beijing Center for Crystal R&D, Key Lab of Functional Crystals and Laser Technology of Chinese Academy of Sciences, TechnicalInstitute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China§University of Chinese Academy of Sciences, Beijing 100049, China∥Department of Physics and Electronic Information Engineering, Minjiang University, Fuzhou, Fujian 350108, China

*S Supporting Information

AB S TRACT : A n e w b e r y l l i u m - f r e e b o r a t eRb3Ba3Li2Al4B6O20F features a layered structure analogous tothat of the solely available deep-ultraviolet nonlinear optical(NLO) material KBe2BO3F2 (KBBF), and thus preserves itsoutstanding linear and nonlinear optical properties to a greatextent. Furthermore, the interlayer bonding in Rb3Ba3Li2Al4-B6O20F is significantly reinforced, with a magnitude of morethan 15.6 times that of KBBF. As a result, a bulkRb3Ba3Li2Al4B6O20F crystal is successfully grown in thepreliminary experiments. The result demonstrates that theRb3Ba3Li2Al4B6O20F crystal may have no (or only a tiny) layering growth habit, which severely hinders the practical applicationsof KBBF. Notably, Rb3Ba3Li2Al4B6O20F overcomes the structural instability problem present in the notable KBBF-familymember Sr2Be2B2O7. These results make Rb3Ba3Li2Al4B6O20F a promising candidate for the next generation of deep-ultravioletNLO materials. First-principles calculations are performed to elucidate the optical properties and structural stability.

■ INTRODUCTION

Deep-ultraviolet (deep-UV, wavelengths below 200 nm)nonlinear optical (NLO) materials, which can double thefrequency of incident light to the deep-UV region, are essentialfor a number of advanced scientific instruments.1−6 Suchmaterials should be of high second-harmonic generation(SHG) efficiency, wide transparent window down to thedeep-UV region, and moderate birefringence to achieve phase-matching, etc.7,8 Limited by these fundamental requirements, todate, only one NLO material KBe2BO3F2 (KBBF)

9 is able todirectly generate deep-UV coherent light in practice. Therequired optical properties in KBBF are mainly ascribed to thelayered structural units (namely, [Be2BO3F2]∞ single-layersperpendicular to the crystallographic c axis), which provide theNLO-active [BO3]

3− units in a perfectly coplanar and alignedarrangement. However, it is still challenging to obtain thickKBBF crystals because KBBF suffers from a severe layeringgrowth habit arising from a very weak interlayer bonding(dominated by K−F ionic bonds) along the c direction.Consequently, the thicknesses of as-grown KBBF crystals arelimited to 3.7 mm so far.10 Moreover, the high toxicity ofberyllium in KBBF makes it urgent to develop new beryllium-free candidates for KBBF.11−16

In order to inherit the brilliant optical advantages whileovercoming the layering growth habit of KBBF, many attemptshave been made to develop the KBBF-family NLO materialswith reinforced interlayer bonding.4,8,11,12,17−19 Especially,Sr2Be2B2O7 (SBBO) was considered to be one of the mostattractive substitutes of KBBF.8 Its structure features [Be2-B2O7]∞ double layers that are interconnected by Sr−O bonds,which enhance the interlayer bonding to about 4.9 times that ofKBBF. Nevertheless, SBBO suffers from a structural instabilityproblem, and as a result, its crystal structure has not been wellsolved yet.16,20

The structural instability problem of SBBO may be resolvedthrough enlarging the space inside the double layers. In 2011,Huang et al. developed a new NLO material NaCaBe2B2O6F(with [Be3B3O6F3]∞ double layers), in whose structure thebridged Be−O bonds inside [Be2B2O7]∞ double layers ofSBBO are replaced by longer Be−F bonds.20 NaCaBe2B2O6Fresolves the instability problem, but the NLO-active [BO3]

3−

groups inside the double layers are in an unfavorablearrangement, which leads to a rather weak SHG response (1/

Received: May 25, 2017Revised: June 16, 2017Published: July 14, 2017

Article

pubs.acs.org/crystal

© 2017 American Chemical Society 4422 DOI: 10.1021/acs.cgd.7b00726Cryst. Growth Des. 2017, 17, 4422−4427

3 × KH2PO4, KDP). Recently, by substituting relatively longerAl−O and Li−F bonds for the bridging Be−O bonds of SBBO,our group successfully developed a new beryllium-free borateK3Ba3Li2Al4B6O20F. This borate consisting of double layerswith an enlarged in-layer space has no structural instabilityproblem and shows brilliant NLO properties.16 Nevertheless,its interlayer bonding is just up to 4.4 × KBBF.In this work, a simple element substitution based on

K3Ba3Li2Al4B6O20F leads to a new beryllium-free KBBF-familyborate, Rb3Ba3Li2Al4B6O20F (hereafter named I). Remarkably, Iexhibits a greatly reinforced interlayer bonding of more than15.6 times that of KBBF. As a result, a bulk I crystal has beengrown in our preliminary experiments, indicating that thelayering growth habit present in KBBF may be overcome. Inaddition, the synthesis, thermal behavior, structure, the NLOproperties, and the first-principles calculations on I are alsoreported in this article.

■ EXPERIMENTAL SECTIONReagents. Rb2CO3, BaCO3, Li2CO3, LiOH·H2O, Al2O3, H3BO3,

LiF, and BaF2 were purchased from Aladdin and used as received. Thepurity of all the reagents is higher than or equal to 99.0%.Synthesis of Polycrystalline I. Polycrystalline powders were

synthesized through the high-temperature solid-state reactions atatmospheric pressure. I powders were prepared by sintering themixture of Rb2CO3 (1.386 g, 0.006 mol), BaCO3 (2.368 g, 0.012 mol),LiOH·H2O (0.168 g, 0.004 mol), Al2O3 (0.816 g, 0.008 mol), H3BO3(1.484 g, 0.024 mol), and LiF (0.104 g, 0.004 mol). First, theaforementioned reactants were finely mixed and ground, followed bytransferring to a platinum crucible for sintering in a muffle furnace.The mixture was gradually heated to 500 °C in 18 h, and subsequentlyheld at 500 °C for no less than 24 h to adequately decompose thereactants before being cooled down to room temperature. Second, theproducts were finely ground and sintered at 650 °C for 150 h beforebeing cooled to ambient temperature. Several intermediate grindingswere performed during the sintering process. As a result, polycrystal-line I can be obtained.The phase purity of the products was verified by powder X-ray

diffraction (XRD) analysis. The parameters of a scanning step width of0.02° and a scanning rate of 0.14° min−1 in the 2θ range of 7−70°were set for collecting the powder XRD patterns. This data collectionwas performed on a Rigaku MiniFlex II diffractometer (Cu Kαradiation) at ambient temperature. The result shows good consistencywith that deduced from single-crystal XRD analysis (see Figure S1 inthe Supporting Information).Crystal Growth. Bulk single crystals of I were successfully

prepared through the top-seeded solution growth method with theLi2O/BaF2/B2O3 self-flux system. A mixture (110 g) of polycrystallineI, LiOH·H2O, BaF2, and H3BO3 (at a molar ratio of 1:8:1:6) was finelyground, and then transferred to a Φ 45 mm × 45 mm platinumcrucible in batches and to be melted at 850 °C in a muffle furnace.Afterward, the platinum was moved to a temperature-programmableelectric furnace for crystal growth. It was quickly heated to 800 °C andheld at this temperature for 48 h to fully melt the mixture.Subsequently, a platinum wire tied to a corundum pole was descendedslowly until immersing into the surface of the melt. The melt wascooled to 720 °C at once and subsequently cooled at 2 °C h−1 until Icrystals crystallized on the platinum wire. The platinum wire was thenlifted out of the melt surface before being cooled to ambienttemperature in 72 h. The crystals separated from the platinum wirewere used as seed crystals to grow bulk single crystals.First, the saturation temperature (∼690 °C) was detected using a

tentative seed crystal method. Second, a seed crystal was fixed to acorundum rod with the aid of platinum wire, which was slowlyimmersed into the melt at 705 °C and then held at this temperaturefor 2 h to dissolve the uneven surfaces of the seed crystal.Subsequently, the temperature was decreased quickly to 690 °Cover 5 min before being cooled at 0.3−1.0 °C per day. After ∼20 days

of crystal growth, the crystal was lifted out of the melt and thetemperature was slowly lowered to ambient temperature. A trans-parent crystal which was cut from the as-grown crystal is as large as 7mm × 5 mm × 4 mm (Figure 1). The (001) face was indexed and

indicated. The thickness along the c axis is about 4 mm, which iscomparable to that of the thickest KBBF crystal to date (3.7 mm alongthe c axis).10 Clearly, the crystal has a block shape and does not showan evident layered growth habit. In comparison, the KBBF crystals arealways lamellar with a small thickness along the c axis, showing a severelayered growth habit.

Single-Crystal Structure Determination. Diffraction datacollection for a single crystal was collected on an Agilent SuperNovaDual diffractometer (Mo Kα radiation, λ = 0.71073 Å). The datacollection and reduction were performed by virtue of the programCrysAlisPro.21 The structure was determined by the direct methodusing SHELXS and refined using the full-matrix least-squares programSHELXL.22 Anisotropic parameters were also applied for therefinements of all atoms. The structure was checked through theADDSYM algorithm from PLATON,23 and no higher symmetrieswere found. Table 1 summarizes the relevant crystallographic data.Additional information is included in the Supporting Information(Tables S1−S3).

Thermal Stability. Differential thermal analysis of I was carriedout using a NETZSCH STA 449C simultaneous analyzer. The crystal

Figure 1. (a) Photograph of a I crystal. (b) Schematic representationof the I crystal with the (001) face being indicated.

Table 1. Crystal Data and Structural Refinement for I

formula Rb3Ba3Li2Al4B6O20Fformula weight (g/mol) 1194.09crystal system hexagonalspace group P6̅2c (190)a (Å) 8.6881(2)c (Å) 16.9483(4)V (Å3) 1107.91(4)Z 2crystal size (mm3) 0.15 × 0.09 × 0.07ρcalcd (g/cm

3) 3.5792temperature (K) 100(2)μ (mm−1) 12.097F (000) 1072data/restraints/parameters 786/0/63R (int) 0.0347GOF (F2) 1.134Flack parameter −0.02(2)final R indices R1 = 0.0238,[Fo

2 > 2σ(Fc2)]a wR2 = 0.0579

final R indices (all data)a R1 = 0.0241,wR2 = 0.0582

aR1 = ∑||Fo| − |Fc||/∑|Fo| and wR2 = [∑[w(Fo2 − Fc

2)2]/∑[w(Fo

2)2]]1/2 for Fo2 > 2σ(Fc

2).

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sample (22.2 mg) placed in an Al2O3 crucible was heated to 1100 °Cfrom ambient temperature at 20 °C min−1, followed by being cooledto ambient temperature at the same rate under flowing nitrogen gas.UV Transmittance Spectrum. The UV optical transmittance

spectrum of I was measured at room temperature using a UV/visible/near-infrared spectrophotometer (Lambda950, PerkinElmer) in thewavelength range of 190−800 nm. A piece of single crystal with athickness of about 1 mm, which was cut from the bulk I crystal (Figure1), was used for the measurement.Second-Harmonic Generation Measurements. According to

the Kurtz−Perry method,24 powder second-harmonic generation of Iwas tested. A Q-switched Nd:YAG laser (1064 nm) served as thefundamental laser. The finely ground crystals were sieved into differentmesh ranges (60−270 meshes). The sieved samples with differentparticle sizes were held using two glass cover slides, and then put intoaluminum holders with an 8 mm diameter hole, which were furtherirradiated by the fundamental laser. The intensity of output light wasrecorded on an oscilloscope by virtue of a photomultiplier tube withan interference filter (535 ± 10 nm). Under the same conditions,sieved KDP crystals were used as the reference.First-Principles Computational Methods. We calculated the

electronic structure of I using CASTEP25 software on the basis ofdensity functional theory (DFT).26 The Perdew−Burke−Ernzerhofffunctional with the generalized gradient approximation27,28 form wasselected to describe the exchange-correlation energy. To model theeffective interaction between atom cores and valence electrons, theoptimized norm-conserving pseudopotentials29 in the Kleinman−Bylander30 form were adopted. Meanwhile, very high kinetic energycutoffs (900 eV) and dense Monkhorst−Pack31 k-point meshes (finerthan 0.04 Å−3 in the Brillouin zones) were used. Our tests found thatthe computational setups adopted above are accurate enough for ourpurposes.Generally, the standard DFT method gives smaller calculated

energy band gaps as compared to the experimental values. Thus, thescissor operators32 were used to shift the conduction band to matchthe calculated band gap with the measured value. The imaginary partof the complex dielectric function was figured out on the basis of theelectron transition from the valence bands to conduction bands. Thereal part of the complex dielectric function can be obtained by virtue ofthe Kramers−Kronig33 transform, and then the refractive indices weredetermined. The SHG coefficients dij were obtained according to theformula proposed by Lin et al.34,35

In order to study the structure stability, we calculated the phononsdispersion spectrum for the title compound based on the linearresponse method.36 This method is an effective way to calculate thesecond derivative of the total energy under a perturbing effect. Thus,the lattice dynamics (or the characterization of atomic interaction) in aconcerned crystal structure can be deduced.

■ RESULTS AND DISCUSSION

Thermal Behavior. For I, only one sharp endothermic peakappears in the vicinity of 860 °C on the DTA curves (FigureS2) with negligible weight loss, indicating that I meltsincongruently. Thus, its large crystals should be grown throughthe flux method below 860 °C.Crystal Structure. I crystallizes into a noncentrosymmeric

hexagonal space group of P6̅2c (No. 190). Its structure iscomposed of alveolate [LiAl2B3O10F]∞ single layers bridged viaAl−O and Li−F bonds or Al−O bonds in the direction of thecrystallographic c axis, resulting in a three-dimensionalframework (Figure 2). Rb+ and Ba2+ cations are located inthe cavities of the framework to keep charge balance. Within a[LiAl2B3O10F]∞ single layer, each B atom is three-foldcoordinated to form a [BO3]

3− triangle with B−O bonddistances ranging from 1.342(6) to 1.391(7) Å and O−B−Obond angles from 119.5(5)° to 124.2(4)°, suggesting that the[BO3]

3− group is nearly coplanar (Figure 2b). The Al/Li atoms

are four-fold coordinated to form AlO4/LiO3F tetrahedra, andthe bond parameters are normal. Notably, the F atoms ofLiO3F tetrahedra all point to the same side of the [LiAl2-B3O10F]∞ layer to connect one adjacent single layer, while theapical oxygen atoms of AlO4 tetrahedra alternately pointupward and downward the [LiAl2B3O10F]∞ single layer tofurther bridge two adjacent single layers (Figure 2c). Thespatial orientations of [BO3]

3− groups are similar to that ofK3Ba3Li2Al4B6O20F, which is beneficial to generate a large SHGresponse.16 The results of bond valence calculations37,38 for Iare summarized in Table S1, indicating that the derivedoxidation states of Rb, Ba, Li, Al, B, O, and F atoms show goodagreement with their expected chemical valence.

Structure Evolution. It is interesting to elucidate thestructural evolution in the KBBF family. As illustrated in Figure3, the structures of the KBBF family evolve from the single-layer structure of KBBF, the double-layer structures of SBBO,and K3Ba3Li2Al4B6O20F, to the infinitely layered structure of I.All of these borates consist of layered structural units withplanar [BO3]

3− groups and tetrahedra (BeO3F tetrahedra forKBBF, BeO4 tetrahedra for SBBO, as well as AlO4 and LiO3Ftetrahedra for K3Ba3Li2Al4B6O20F and I). As compared toKBBF with a very weak interlayer connection (K−F bonds),the interlayer connection for the rest of the aforementionedborates (dominated by Sr−O bonds for SBBO, Ba−O bondsfor K3Ba3Li2Al4B6O20F, and Al−O and Li−F bonds for I,respectively) is significantly reinforced, thereby weakening thetendency of layering growth for their single crystals.In order to evaluate the layering growth habit, we quantified

the interlayer connection through computing the layeredelectrostatic force according to the Coulomb’s law, given thatthe interlayer bonds are basically ionic.11,12,39 This method hasbeen adopted in our previous works,11,12 and the results arewell consistent with the experimental observation. Theelectrostatics force magnitude of one interlayer bond (bridgingbond between two adjacent layers) can be calculated using thefollowing equation

| | =| ∗ |

Fk q q

re 1 2

2

where ke is the electrostatic constant (given that all the bondssubmerged in the same dielectric media), q1 and q2 are thecharge magnitude of the two bonding ions, respectively, and r isthe bond distance. As shown in Table 2, due to the relativelylarge charge magnitude and short bond distances, theelectrostatic interaction force of one Al−O bond in I reaches

Figure 2. (a) Crystal structure of I. (b) One [LiAl2B3O10F]∞ singlelayer. (c) One [LiAl2B3O10F]∞ single layer viewed along the b axis.Blue triangles in (b) and (c) represent [BO3]

3− groups.

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15.6 × K−F bond in KBBF, which is far larger than those ofother ion bonds such as Sr−O and Ba−O. Considering thatAl−O bonds are partially covalent, the interaction force of Al−O bonds should be larger than the calculated values. As weknow, the interlayer connection is dominantly determined bythe relatively strong bridging bonds between the adjacentlayers. In I, the strong Al−O bonds rather than the weak Ba−Obonds, determine the interlayer bonding. Such a stronginterlayer bonding is very beneficial to the growth of thick Icrystals.Unlike the double-layer structure of K3Ba3Li2Al4B6O20F, I

possesses a different layered structure whose single layers areinfinitely interconnected via Al−O or Li−F bonds along the caxis. From the viewpoint of structural stability, when the K+

cations are replaced by the relatively larger Rb+ cations, the[Li2Al4B6O20F]∞ double layers may be too crowded (Figure 4).We proposed that, to maintain the structural stability, half ofthe Al−O bridging bonds of K3Ba3Li2Al4B6O20F are squeezedout of the double layers and further serve as new bonds toconnect the adjacent double layers in the direction of thecrystallographic c axis (Figure 4c,d), finally constructing thethree-dimensional framework of I. On the other hand, thisstructural difference results in distinct interlayer bonding inboth borates (4.4 × KBBF in K3Ba3Li2Al4B6O20F vs 15.6 ×KBBF in I). The structural convergence factor is as small as0.0238 (in comparison, SBBO > 0.065),8 indicating that I isstructurally stable. In our preliminary experiments, a bulk Icrystal was successfully grown (Figure 1), providing a solidevidence for its structural stability. The first-principlescalculations displayed in the following section of this articlealso support this conclusion.Nonlinear Optical Property and UV Transmittance

Spectrum. Since I has similar layered structural units similar tothat of KBBF, it is expected to possess similar SHG response.We measured the powder SHG intensity based on the Kurtz−Perry method.24 As illustrated in Figure 5a, the powder SHG

intensities for the titled compound reach approximatelysaturated values with increasing particle sizes, indicating that Iis phase-matching at the fundamental laser of 1064 nm basedon the rule proposed by Kurtz and Perry.24 The SHG efficiencyin the particle size range of 180−250 μm is about 1.4 times thatof KDP. Obviously, the SHG response is close to that of KBBF(∼1.21 × KDP)40 and is much larger than that of NaCaBe2B2-O6F (1/3 × KDP)9 without a structural instability problem. Inorder to ascertain the cutoff edge, a thin I crystal with a

Figure 3. Structural evolution from (a) KBBF, to (b) SBBO, to (c) K3Ba3Li2Al4B6O20F, and (d) I. Element substitution is indicated for these borates.

Table 2. Comparison of the Interlayer Bonding for SelectedKBBF-Family NLO Materials

species bonds lengths (Å) q1a q2

a |F|b

KBBF K−F 2.755 1 1 1Sr2Be2B2O7 Sr−O 2.478 2 2 4.9K3Ba3Li2Al4B6O20F Ba−O 2.639 2 2 4.4I Ba−O 2.642 2 2 4.3

Al2−O 1.709 3 2 15.6Al1−O 1.685 3 2 16.0

aIn multiples of 1.602 × 10−19 C. bIn multiples of |FKBBF|.

Figure 4. (a) The variation of interlayer Al−O bonds from (a)K3Ba3Li2Al4B6O20F to (b) I. Element substitution is indicated and Li−F bonds have been omitted for the sake of clarity. The schematicillustration for the rotation of Al−O bridging bonds from (c) onedouble layer of K3Ba3Li2Al4B6O20F to (d) the corresponding layer of I.The violet arrows in (c) are drawn to show that the Al−O bridgingbonds turn up and down from the double layer.

Figure 5. (a) SHG intensity vs particle size curves for I. The solidcurves are drawn to guide the eyes and are not fits to the data. (b) UVoptical transmittance spectrum on a thin crystal.

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thickness of about 1 mm was used to carry out themeasurement of the transmittance spectrum. As shown inFigure 5b, its absorption edge is located at about 195 nm. Thecombination of deep-UV transparent performance andmoderately phase-matching SHG efficiency makes I satisfythe fundamental optical requirements as a promising deep-UVNLO candidate.First-Principles Calculations. In order to explain the

origins of the NLO property and structural stability, weperformed the first-principles calculations on density of states(DOS), NLO coefficients, birefringence, and phonon dis-persion spectrum. The electronic band structure of I crystal isshown in Figure 6a, exhibiting the calculated energy band gap

of 3.875 eV. The DOS and partial DOS for I are plotted inFigure 6b, from which one may obtain the following electroniccharacteristics: (i) The upper part of the valence bandpredominantly consists of the p orbitals of O (2p) and B(2p). (ii) The bottom part of the conduction band isconstituted by orbitals of all atoms. Because the opticalproperties of a material are dominated by the electronictransitions from the valence band to the conduction band nearthe band gap,41 the [BO3]

3− building units have a predominantcontribution to the optical properties in I and the contributionsof other ions (Li+, Rb+, Ba2+, Al3+, F−) are negligibly small.On the basis of the calculated electronic structure, the

derived birefringence value for I at the wavelength of 532 nm isΔn = 0.044 (Figure S3). Such a birefringence value is moderateas compared to those of KBBF and K3Ba3Li2Al4B6O20F and isfavorable to achieve phase-matching, as proved by the powderSHG tests. Meanwhile, under the restriction of Kleinman’ssymmetry,42 I has only one nonzero independent SHGcoefficient. The calculated SHG coefficient for I is d22 =−0.47 pm V−1, which shows good consistence with the result ofpowder SHG measurement (given d36 (KDP) = 0.39 pmV−1).43 The structural stability of I is also confirmed by thecalculated phonon dispersion spectrum, which is wellestablished to intrinsically characterize the interatomicinteraction. If a crystal structure is kinetically unstable, theimaginary phonon modes (or negative phonon eigenvalues)would occur because of the repulsive forces between atoms atcertain lattice points of reciprocal space.44 Our previous

calculations on the phonon modes16 for SBBO, NaCaBe2B2-O6F, and K3Ba3Li2Al4B6O20F are consistent with their structuralstability. As shown in Figure 7, there are no negative phononmodes in the phonon dispersion spectrum, confirming that Iovercomes the structurally dynamical instability theoretically.

■ CONCLUSIONIn summary, a new beryllium-free KBBF-family NLO materialRb3Ba3Li2Al4B6O20F has been successfully developed. Itfeatures a layered structure similar to that of KBBF and thusexhibits NLO properties comparable to that of KBBF.Remarkably, because of the effect of counterpart cations, itexhibits a greatly reinforced interlayer bonding with amagnitude of ≥15.6 × KBBF, being greatly stronger thanthose of most KBBF-family materials. Consequently, we havesuccessfully grown a bulk Rb3Ba3Li2Al4B6O20F crystal withoutan evident layering growth habit. In addition, the titlecompound overcomes the structural instability problem thatexists in the notable KBBF-family member SBBO. Thesefindings indicate that Rb3Ba3Li2Al4B6O20F is a promisingcandidate for next-generation deep-UV NLO materials. Ourfuture work will be devoted to growing large Rb3Ba3Li2Al4-B6O20F crystals with high quality for practical applications. Themodulation of interlayer bonding in layered materials may shedhelpful highlights on the controllable design and synthesis ofnew deep-UV NLO materials.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.cgd.7b00726.

Figures S1−S3, tables of atomic coordinates, bondlengths, and angles, and anisotropic thermal parameters(PDF)

Accession CodesCCDC 1519543 contains the supplementary crystallographicdata for this paper. These data can be obtained free of chargevia www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The CambridgeCrystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: +44 1223 336033.

■ AUTHOR INFORMATIONCorresponding Authors*E-mail: jhluo@fjirsm.ac.cn (J.L.).*E-mail: zhaosangen@fjirsm.ac.cn (S.Z.).

Figure 6. (a) Electronic band structure of I. (b) DOS and partial DOSplots of I.

Figure 7. Phonon dispersion spectrum of I.

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*E-mail: zslin@mail.ipc.ac.cn (Z.L.).

ORCIDJunhua Luo: 0000-0002-7673-7979Author ContributionsThe manuscript was written through contributions of allauthors. All authors have given approval to the final version ofthe manuscript.

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

This work was supported by the NSFC (21571178, 21525104,91622118, 51502288, 51402296, and 91422301), the StrategicPriority Research Program of Chinese Academy of Sciences(XDB20000000), and the 863 Program of China(2015AA034203). S.Z. is grateful for the support from theNSF for Distinguished Young Scholars of Fujian Province(2016J06012).

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Crystal Growth & Design Article

DOI: 10.1021/acs.cgd.7b00726Cryst. Growth Des. 2017, 17, 4422−4427

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