We have recently prepared solid solutions of Ba∼6.3Ca∼0.7F12Cl2−xBrx with x ranging from 0 to 2. In this work, the synthesis and single crystal X-ray structure of calcium-free crystals of Ba∼6.9Na∼0.2F12Br0.6Cl1.4 (space group P63/m, a=10.6024(10), c=4.2034(4)Å), Ba∼6.9Na∼0.2F12Br1.4 Cl0.6 (space group P63/m, a=10.6155(9), c=4.2355(4)Å) and Ba∼6.9Na∼0.2Br1.32Cl0.68F12 (space group P63/m, a=10.6218(9), c=4.2284(4)Å) are reported. These crystals systematically present additional electron density at the 0 0 0.25 position which is associated with the presence of small, but significant amounts of Na+ ions in the crysta

Hagemann, H.

Kubel, F.

Penhouet, T.

Rief, A.

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ORIGINAL PAPERCalcium-free Solid Solutions in the System Ba7F12Cl2–xBrx(x \ 1.5), a Single-component White Phosphor HostT. Penhouet Æ H. Hagemann Æ F. Kubel ÆA. RiefReceived: 23 October 2006 / Accepted: 12 March 2007 / Published online: 9 May 2007 Springer Science+Business Media, LLC 2007Abstract We have recently prepared solid solutions ofBa~6.3Ca~0.7F12Cl2–xBrx with x ranging from 0 to 2. In thiswork, the synthesis and single crystal X-ray structure ofcalcium-free crystals of Ba~6.9Na~0.2F12Br0.6Cl1.4 (spacegroup P63/m, a = 10.6024(10), c = 4.2034(4) A˚), Ba~6.9-Na~0.2F12Br1.4 Cl0.6 (space group P63/m, a = 10.6155(9),c = 4.2355(4) A˚) and Ba~6.9Na~0.2Br1.32Cl0.68F12 (spacegroup P63/m, a = 10.6218(9), c = 4.2284(4) A˚) are re-ported.These crystals systematically present additional electrondensity at the 0 0 0.25 position which is associated with thepresence of small, but significant amounts of Na+ ions inthe crystal.Keywords Barium fluorohalide  Solid solution Single crystal X-ray diffractionIntroductionAlkaline earth fluoro-halides are interesting host materialsfor optical applications. Crystals of the matlockite family(PbFCl-structure) have attracted substantial interestbecause of several applications such as X-ray imaging oroptical hole burning at ambient temperatures [1]. The newcompound Ba7F12Cl2 and its derivatives have been pat-ented as a new, single component white phosphor material[2]. Ba7F12Cl2 crystallizes in two modifications, one or-dered (space group P-6) and one disordered (space groupP63/m) [3]. Very recently, we have demonstrated that thedisordered form contains small amounts of Na+ ions,yielding a refined composition Ba~6.9Na~0.2F12Cl2 [4].The formation of solid solutions (desirable to tune theoptical properties of doped crystals) starting from nomi-nally Ba7F12Cl2 can be approached both by replacing Bawith another divalent ion, and by replacing Cl with Br. Wehave previously reported the crystal structures ofBa6EuF12Cl2 [5] and of the solid solutions Ba~6.3-Ca~0.7F12Cl2–xBrx [6]. In this latter work, the experimentalpreparation conditions required the presence of Ca2+ in thereaction mixture to obtain bromide substituted singlecrystals.In this work we address the formation of single crystalsof Ba7F12Cl2–xBrx (x < 1.5) without Ca. The effect of thesubstitution of chloride by bromide on the emission spectraof these white phosphors is briefly discussed.ExperimentalSingle crystals were obtained by slow cooling (0.1 K/min) of melts containing alkali halides (LiCl, LiBr, NaCland NaBr) and BaF2 under inert atmosphere in graphitecrucibles. Both pure and Eu(II)––doped (Eu:Ba ratio<0.01) samples were prepared. The presence of Eu(II) inthese concentrations did not influence the crystalstructure.Dedicated to the memory of Professor Erwin Parthe´, deceased August28 2006.The synthesis and single crystal X-ray structures ofBa7F12Cl2–xBrx (x £ 1.4) including small amounts of Na in the 0 00.25 position are reported.T. Penhouet  H. Hagemann (&)De´partement de Chimie Physique, Universite´ de Gene`ve, 30,quai E. Ansermet, 1211 Geneva, Switzerlande-mail: hans-rudolf.hagemann@chiphy.unige.chF. Kubel  A. RiefInst. fu¨r Chemische Technologie und Analytik, TU Wien,Getreidemarkt 9/164, 1060 Vienna, Austria123J Chem Crystallogr (2007) 37:469–472DOI 10.1007/s10870-007-9195-8Individual single crystals were mechanically separatedand selected under polarized light for single crystal struc-ture determinations.Additional solid state reactions of stoichiometric mix-tures of Ba7F12Cl2–xBrx (starting from 6BaF2 + (2 – x)BaCl2 + xBaBr2) over the entire composition range wereperformed.X-ray measurements were obtained using a SiemensSMART diffractometer with a graphite monochromatorand a SMART APEX detector.Luminescence spectra were obtained using a Fluorologinstrument.Results and DiscussionsSynthesisWe have performed systematic solid state preparations ofstoichiometric mixtures corresponding to Ba7F12Cl2–xBrxover the entire composition range with an annealing tem-perature of 750 C under inert atmosphere. X-ray powderdiffraction shows that up to x = 1.4, the ordered form ofBa7F12Cl2–xBrx is obtained (space group P-6), as well assome BaF2 (ca 20 wt%). For x > 1.5, the only phasesfound were BaF2 and BaFCl1–yBry. Es-Saski et al. [7]equally reported this limit of bromide substitution inBa7F12Cl2–xBrx by solid state reaction.Single crystals of Ba7–yCay F12Cl2–xBrx with y . 0.7(disordered modification, space group P63/m) have beenprepared previously [6] from mixtures of: BaF2 + -CaF2 + NaCl + NaBr. The corresponding lattice parame-ters are collected in Fig. 1 and compared with those ofsamples prepared in this study.Initial experiments with mixtures of BaF2 + NaCl + -NaBr did not appear to favour the introduction of bromideions in the structure. However, the addition of LiCl andLiBr to the reaction mixture resulted in the successfulpreparation of Ba7F12Cl2–xBrx. However, also with this fluxcomposition the highest bromide content was limited to thecomposition Ba7F12Cl0.6Br1.4.Typical reaction conditions leading to well developedcrystalline needles of 2–3 mm length were: 5 gBaF2 + 0.44 g NaBr + 0.077 g LiBr + 0.144 g LiCl, cor-responding to a molar ratio of NaBr:LiBr:LiCl of 5:1:4respectively. This mixture was heated under inert atmo-sphere to 950 C and then cooled in 50 h to 650 C.Besides the desired product, about 10 wt% of LiBaF3and 5 wt% of BaF2 were identified by powder X-ray dif-fraction in the reaction mixtures.Single Crystal Structure DeterminationsCrystal structure data for the crystals Ba~6.9-Na~0.2F12Br0.6Cl1.4, Ba~6.9Na~0.2F12Br1.4 Cl0.6 and Ba~6.9-Na~0.2Br1.32Cl0.68F12 are collected in Tables 1 and 2.Similarly to our recent results for Ba7F12Cl2 [4], all singlecrystal refinements for these samples with space group P63/m present an additional electron density at the 0 0 0.25position. This electron density has been associated [4] withthe presence of additional Na+ ions in this six-fold fluoridecoordinated site with typical Na–F bond length of 2.22–2.23 A˚. For the final crystal structure refinements, thepopulations of the Ba2 and the Na site were refined inde-pendently to obtain an unbiased estimate of the Na content.In our previous work [4], the refined Na content wasconfirmed quantitatively by chemical analysis. Within thestandard deviations, the charges are balanced.The crystal structure is illustrated in Fig. 2. Ba1 iscoordinated by fluoride and bromide (or chloride), whileBa2 is only coordinated by fluoride. The refined Na and Bacontents are very similar for all samples with differentbromide content (see Table 2), and can be summarizedwith the overall formula Ba~6.9Na~0.2F12X2. As Na ismonovalent and Ba bivalent, one obtains thus an overfillingof the 00z channel, as discussed in [4]. Further details ofthe crystal structure investigations may be obtained inwriting from the Fachinformationszentrum Karlsruhe,76344 Eggenstein–Leopoldshafen, Germany, on quotingthe depository numbers CSD 417033, 417020 and 417032.Comparison of the unit cell volume as a function ofbromide content show that Vegard’s law applies for thisseries of compounds, as it does for Ba6.3Ca0.7F12X2 [6].Figure 3 compares the Ba–Cl,Br bond length for bothseries of compounds and shows that the refined bromidecomposition correlates even better with the Ba–Cl,Br bondlength than with the lattice parameters a and c taken sep-arately (see Fig. 1). It appears that this bond length issystematically larger in the Ca containing compounds.4154174194214234254274291050a [pm]]mp[c1052 1054 1056 1058 1060 1062 1064Fig. 1 Comparison of the lattice parameters for Ba6.3Ca0.7F12X2[6](open squares) and calcium-free (filled diamonds) Ba7F12X2(X = Cl2–xBrx) single crystals. The lines are drawn to guide the eye470 J Chem Crystallogr (2007) 37:469–472123Table 1 Crystal dataCSD number 417033 417020 417032Formula Ba~6.9Na~0.2F12Br0.6Cl1.4Ba~6.9Na~0.2F12Br1.4 Cl0.6Ba~6.9Na~0.2F12Br1.3Cl0.7Mass [g mol–1] 1280.4 1308.4 1306.2Crystal system/space group Hexagonal, P63/ma = b (A˚) 10.6024(10) 10.6155(9) 10.6218(9)C (A˚) 4.2034(4) 4.2355(4) 4.2284(4)V (A˚)3 409.20(9) 413.35(8) 413.15(11)Z 1Density [g cm–1] 5.30 5.25 5.25Crystal size [mm] 130 · 60 · 35 130 · 70 · 50 170 · 50 · 35Diffractometer type Siemens SMARTRadiation [A˚] MoKa 0.71073Temperature [K] 293 K( range [] 2.22–28.23 2.22–28.13 2.21–28.17nref measured 2879 2888 2880nref independent 383 385 386Rint [%] 2.74 1.68 2.24Absorption correction NumericalAbsorption coefficient l [mm–1] 19.271 19.078 19.087Program used Xtal 3.2.nref with I > 3s(I) 352 369 355R (Rw) [%] 1.72 (1.61) 2.49 (2.07) 1.55 (1.50)Goodness of fit [%] 1.80 2.35 2.00Table 2 Refined populationsand selected bond lengthSample Ba~6.9Na~0.2F12Br0.6Cl1.4 Ba~6.9Na~0.2F12Br1.4Cl0.6 Ba~6.9Na~0.2F12Br1.3Cl0.7Population Ba2 0.438(1) 0.429(1) 0.437(1)Population Cl 0.696(3) 0.291(3) 0.338(3)Population Na22 0.083(5) 0.100(5) 0.094(4)Ba–X (A˚) 3.3534(3) 3.3863(3) 3.3825(2)Na–F (A˚) 2.228(3) 2.221(4) 2.229(3)Fig. 2 Projection along the c-axis of the crystal structure ofBa~6.9Na~0.2F12Br1.4 Cl0.63.323.333.343.353.363.373.383.393.43.413.420 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Br/Cl+Br mole fraction]A[htgneldnobrB,lC-aBFig. 3 Ba–Cl,Br bond length versus refined bromide content inBa6.3Ca0.7F12X2 [6] (squares) and in Ba~6.9Na~0.2F12X2 (diamonds)J Chem Crystallogr (2007) 37:469–472 471123Figure 4 shows the effect of replacing chloride by bro-mide on the emission spectra of these single componentwhite phosphors. Both materials present a large emissionspectrum ranging over a vast part of the visible spectrum(from 400 to 700 nm). The lower wavelength emissionband at ~450 nm is similar to the emission observed at440 nm in Eu-doped Ba12F19Cl5 [8] which presents asimilar fluoride and chloride environment than the Ba1 inBa7F12Cl2. The band at 565–590 nm can be related toEu(II) on the site of the Ba2 ion coordinated by 9 F atoms(in the 00z channel) [9].The introduction of bromide shifts the higher emissionband from about 590 to lower wavelength (~565 nm),which corresponds visually to the transition from a slightlyyellowish emission to a white emission.ConclusionsIn contrast to the Ca-containing compounds Ba~6.3-Ca~0.7F12Cl2–xBrx, it appears that the maximum Br–Cl ratiowhich can be obtained in the absence of other bivalent ionsbesides Ba2+ in Ba7F12Cl2–xBrx is reached for x  1.5.Crystals of the disordered modification show systemati-cally additional electron density at the 0 0 0.25 site whichcorresponds to a small, but constant (independent of bro-mide substitution) amount of Na+ ions in the structure.Supplementary DataFurther details of the crystal structure investigations maybe obtained in writing from the FachinformationszentrumKarlsruhe, 76344 Eggenstein-Leopoldshafen, Germany, onquoting the depository numbers CSD-417033, 417020 and417032.Acknowledgements This work was supported by the Swiss Na-tional Science Foundation (Projects 200021-101950 and 200020-109422).References1. Bill H, Jaaniso R, Hagemann H, Lovy D, Monnier A, Schnieper M(1995) Opt Eng 34:23332. Hans Bill, Hans Hagemann and Frank Kubel PCT Int Appl WO 9917,340 (Cl H01J61/44), 8 Apr 1999, CH Appl 97/2,277, 29 Sep1997, 27pp3. Kubel F, Bill H, Hagemann H (1999) Z Anorg Allg Chem 625:6434. Kubel F, Hagemann H (2006) Cryst Res Technol 41:10055. Kubel F, Bill H, Hagemann H (2000) Z Anorg Allg Chem626:17216. Fru¨hmann B, Kubel F, Hagemann H, Bill H (2004) Z Anorg AllgChem 630:14847. Es-Sakhi B, Garcia A, Struye L, Willems P, Leblans P, MouddenA, Fouassier C (2002) Mater Sci Eng B96:2338. Rey JM, Bill H, Lovy D, Kubel F (1999) J Phys Condensed Matter11:73019. Rey JM, PhD Thesis, University of Geneva, 200012x106108642snetnInoissimE].u.a[yti700650600550500450400Emission Wavelength [nm]Fig. 4 Comparison of the emission spectra of Eu-doped Ba~6.9-Na~0.2F12Cl2 (dashed line) and Ba~6.9Na~0.2F12Br1.32Cl0.68 (full line).T = 300K, kexcitation = 340 nm472 J Chem Crystallogr (2007) 37:469–472123

Calcium-free Solid Solutions in the System Ba7F12Cl2−xBrx (x<1.5), a Single-component White Phosphor Host

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Calcium-free Solid Solutions in the System Ba7F12Cl2−xBrx (x<1.5), a Single-component White Phosphor Host

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