Mat. Res. Bull. Vol. 14, pp. 1529-1534, 1979. Printed in the USA. 0025-5408/79/121529-06502.00/0 Copyright (c) 1979 Pergamon Press Ltd.

SYNTHESIS AND CHARACTERIZATION OF EUROPIUM(II)-HOLOBORATES, Eu2B509C1 AND Eu2B509Br

K. Machida, T. Ishino, G. Adachi* and J. Shiokawa Department of Applied Chemistry, Faculty of Engineering, Osaka University, Yamadakami, Suita, Osaka 565, Japan

(Received October 11, 1979; Communicated by W. White)

ABSTRACT Europium(II)-haloborates, Eu2B509CI and Eu2B509Br, were synthesized and characterized by X-ray analysis, magnetic susceptibility and luminescent spectral measurements. The chloroborate Eu2B5OaCI crystallizes in the tetragonal system, D~-P42212 , with cell dimensions: a=i1.349(4), c= 6.500(4)A and Z=4, and Eu2B509Br in the orthorhombic system, C½~-Pnn2 or D½~-Pnnm, with cell dimensions: a=ii.503(3), b=ii.382(3), c=6.484(2)~ and Z=4. Both of them were para- magnets with paramagnetic Curie temperature at about -i K, and band emissions peaking at about 430 and 435 nm which were based on a 4f7-4f65d transition of Eu 2+ ion were ob- served on Eu2B509CI and Eu2B509Br , respectively.

Introduction

Compounds containing Eu 2+ ions have been synthesized on account of their magnetic and spectroscopic properties. Among Eu(II)- borates, EU3B206 (I) has been found to be a ferromagnet with Tc= 7.5 K, EuB204 (2) to be antiferromagnetic below about 3 K, and EuB407 (3) to give a band emission at about 370 nm. However in a ternary system EuO-EuX2(X=CI,Br)-B203 no compound has been obtained.

The present paper reports on the synthesis of Eu2B509C1 and Eu2B509Br , and their magnetic and luminescent properties.

Experimental

Preparation. Eu(II)-haloborates were prepared from the follow- ing starting materials: EuB204, EuX 2 and B203(99.5 %). The prepa-

*Author for correspondence.

1529

1530 K. MACHIDA, et al. Vol. 14, No. 12

ration method of EuB204 had been described in Ref.(2) and EuX 2 was obtained by heating th4 mixture of EuX3.nH20 and a large excess of reagent grade NH4X in a reducing atmosphere H 2 at 600-700 °C for several hours. When the appropriate amounts of EuB204, EuX 2 and B203 (mole ratio = 1.5:0.7-0.8:1.0) were fully mixed and pelletized, and then heated in an inert gas He at 1050 °C for 2 hours, Eu2B509CI or Eu2B509Br was formed. The excess of EuX 2 was used in the above process because EuX 2 tended to vaporize at high temperature. The unreactive EuX 2 served as a flux and was removed from the resulting materials by washing with methanol. Both of haloborates have congruent melting points at about ii00 °C, and fine single crystals were obtained by melting at 1130 °C and allowing to cool at 4-5°C/ hour to 950 °C. The crystal habits were prismatic for Eu2B509CI and needle-like for EU2B509Br and their colors were light-yellow.

Characterization. The compositions of resulting materials were determined by using the EDTA titration, the atomic absorption and the AgX gravimetric methods for Eu, B and X elements, respec- tively.

X-ray powder analysis was performed with the Ni-filtered CuK~ radiation (I=1.5418 A) on a Rigaku Rota-flex diffractometer. The accurate unit cell constants of samples were determined by the least-squares method. The diffractometer was calibrated with high purity silicon (99.999 %).

The magnetic and ultraviolet luminescent measurements were carried out according to the methods described elsewhere (2,3).

Results and Discussion

The results of chemical analyses on resulting materials are summarized in Table i. The experimental values for the ele- ments of Eu, B and X are in agreement with the theoretical values. The small differences between the experimental and theoretical values for B and Br

TABLE I.

Analytical data for Eu(II)-haloborates

Composition Atom fraction per formula weight Eu B X

Eu2B509CI 2.06 5.31 0.96

Eu2B509Br 2.01 5.28 0.85

seem to be due to the low sensitivity of atomic absorption analysis and the loss of the HBr gas evolved by dissolving Eu2B509Br in a conc. HNO 3 solution, respectively.

X-ray diffraction patterns of Eu(II)-haloborates are summarized in Tables 2 and 3, and they are indexed on the basis of the patterns of Sr-analogs (4), which are expected to be isostructural with Eu(II)-haloborates. The crystallographic data of Eu(II)-haloborates are summarized in Table 4. The chloroborate Eu2B509CI crystallizes in the tetragonal system with cell dimensions: a=ii.349(4), c=6.500 (4) ~ and Z=4, and Eu2B509Br in the orthorhombic system with cell dimensions: a=ii.503(3), b=ii.382(3), c=6.484(2) A and Z=4. They

Vol. 14, No. 12 Eu2B509CI AND Eu2B509Br 1531

TABLE 2

X-ray diffraction data for Eu2B509CI

o o o o 0 o

hkl do(A ) dc(A ) I/I 0 hkl do(A) de(A ) I/I 0 hkl do(A) dc(A ) I/I 0

020 5.68 5.68 25 331 2.471 2.474 10 351 1.861 1.865 25 011 5.64 5.64 65 132 2.406 2.409 5 133 1.856 1.855 15 120 5.07 5.08 10 241 2.358 2.364 5 152 1.841 1.836 5 iii 5.05 5.05 i0 340 2.267 2.270 10 260 1.798 1.794 10 220 4.01 232 2.261 2.261 i0 161 1.796 1.793 5 121 4.00 4.00 70 051 2.147 2.143 i0 233 1.786 1.785 i0 221 3.41 3.41 5 042 2.140 2.137 20 450 1.775 1.772 5 031 3.27 3.27 20 013 2.132 2.128 15 252 1.768 1.768 5 002 3.26 3.25 25 250 2.108 2.107 10 451 1.710 230 3.14 3.15 15 142 2.096 2.100 30 442 1.710 1.707 10 131 3.13 3.14 20 113 2.092 2.092 15 143 1.706 1.703 i0 112 3.00 3.01 i0 332 2.071 2.065 5 360 1.702 1.692 5 040 2.854 2.837 40 440 2.006 333 1.685 1.684 5 022 2.821 2.820 100 251 2.004 2.005 20 361 1.638 1.637 5 140 2.748 2.753 5 242 1.996 2.000 30 062 1.633 1.635 5 122 2.739 2.737 25 123 1.991 1.993 15 004 1.622 1.625 5 330 2.673 2.675 5 350 1.946 1.946 5 162 1.613 1.618 5 240 2.540 2.538 15 060 1.896 1.892 5 460 1.574 1.574 5 141 2.532 2.535 15 033 1.882 1.880 10 071 1.581 1.573 10 222 2.525 2.525 30 160 1.865 1.866 15 262 1.566 1.571 10

TABLE 3

X-ray diffraction data for Eu2B509Br

o 0 o o 0 0

hkl d o (A) d c (A) I/I 0 hkl d o (A) d c (A) I/I 0 hkl d o (A) d e (A) I/I 0

200 5.77 5.75 15 022 2.820 2.817 60 511 2.130 2.130 15 020 5.72 5.69 20 410 2.787 2.788 15 103 2.125 2.124 35 101 5.70 5.65 35 140 2.765 2.762 30 013 2.120 2.123 15 011 5.67 5.63 80 212 2.745 2.741 15 250 2.116 2.117 10 210 5.15 5.13 20 122 2.738 2.736 25 412 2.114 2.114 20 120 5.11 5.11 20 330 2.697 2.697 10 151 2.111 2.111 45 iii 5.07 5.06 15 420 2.564 2.567 30 142 2.106 2.103 30 220 4.05 4.05 55 411 2.560 2.561 35 113 2.089 2.088 15 211 4.03 4.03 35 240 2.552 2.550 35 332 2.075 2.073 10 121 4.02 4.01 20 141 2.543 2.541 40 440 2.021 2.023 20 310 3.64 3.63 5 222 2.531 2.530 20 422 2.012 2.012 35 130 3.60 3.60 5 331 2.491 2.490 20 251 2.012 221 3.44 3.43 5 312 2.421 2.419 10 242 2.006 2.005 35 301 3.31 3.30 50 132 2.412 2.410 I0 213 1.993 1.992 25 031 3.29 3.28 70 421 2.384 2.386 i0 123 1.989 1.990 15 002 3.25 3.24 20 241 2.374 2.373 5 530 1.970 1.967 5 320 3.18 3.18 45 430 2.291 2.292 i0 350 1.956 1.957 i0 311 3.18 3.17 45 340 2.284 2.285 20 600 1.916 1.917 5 230 3.17 3.17 40 501 2.176 2.168 I0 060 1.896 1.897 i0 131 3.15 3.15 45 431 2.161 2.161 25 610 1.892 1.891 10 112 3.01 3.01 30 341 2.155 2.155 30 303 1.883 20 400 2.875 2.876 i00 402 2.151 2.151 20 531 1.882 1.883 321 2.857 2.855 40 051 2.147 2.148 15 033 1.875 1.878 20 231 2.846 042 2.140 2.139 10 351 1.872 1.874 35 040 2.847 2.846 i00 520 2.132 2.133 i0 160 1.868 1.872 25 202 2.826 2.824 40

1532 K. MACHIDA, et al. Vol. 14, No. 12

b~ong to the1~ollowing space groups: D~-P42212 for Eu2B509CI and C~v-Pnn2 or. D~-Pnnm for Eu2B509Br, respectively. Their densities (Dx) are in good agreement wlth the measured values (Dm).

TABLE 4

Crystallographic data for Eu(II)-haloborates

Lattice Density (g/cm 3) Z Compound Symmetry parameters (A) S .G. Dx Dm

a=ii.349(4) D~-P422 2(94) 4 27 4.30 4 Eu2B509CI Tetragonal c = 6.500(4) 1 •

a=ll. 503 (3) cl0-Pnn2 (34) Lv Eu2B509Br Orthorhombic b=ii.382(3) 12 or 4.55 4.53 4

c= 6.484(2) D2h-Pnnm (58)

The magnetic susceptibility measurements were carried out on Eu(II)-haloborates over a temperature range: 77-300 K. In Table 5 their magnetic data are summarized, and they are paramagnetic over the measured temperature range. The values of their effective magnetic moments per Eu 2+ ion (~eff.) are 7.81 and 7.73 ~B for Eu2B509CI and Eu2B509Br respectively, which almost agree with the theoretical value 7.94 ~B- Their paramagnetic Curie temperatures (0 c) are about -i K, and hence they are expected to be paramagnetic even at the lower temperature, e.g. liquid He temperature.

TABLE 5

Magnetic and luminescent data for Eu(II)-haloborates

Compound ~eff.(~B) 8c(K) lmax(nm) I/2(nm) Q.E.(%)

Eu2B509CI 7.81 -i 430 30 10

Eu2B509Br 7.73 -i 435 30 5

The luminescent properties of resulting materials are shown in Table 5 and Fig.l. They qive band emissions with the half-width of 30 nmbased on the 4f7-4f65d transition of Eu 2+ ions, which are peaking at 430 and 435 nm for Eu2B509CI and Eu2B509Br respectively and of which the excitation patterns are peaking at about 410 nm and broad. The quantum efficiency at 254 nm excitation and 300 K is about i0 % for Eu2B509CI and about 5 % for Eu2B509Br , and these values are noticeable to be relatively great among Eu(II)-compounds of which the quantum efficiency should be largely influenced by a concentration quenching effect.

In Table 6 the luminescent data for Eu(II)-borates are quoted from Ref.(3), and EuB204 and EuB407 give band emissions at about 370 nm while the emission can not be observed on Eu3B206 and Eu2B205. Their quantum efficiencies depend on the corresponding borate units. The tetraborate EuB407 of which the value of quantum efficiency (about 7 %) is the greatest in the known Eu(II)-borates consists of

Vol. 14, No. 12 Eu2B509C1 AND Eu2B509Br 1533

100 250 300 350 400 450 500 550

J Excitation ~ I Emission

I I ~ i l l

0 250 300 350 400 450 500 550 = IA (nm)

FIG. 1

Relative emission and excitation spectra and diffuse reflection spectra at 300 K of (a) Eu2B509CI and (b) EU2B509Br

5O

&= so

a three-dimensional network of tetr~hedral BO 4 units and each Eu z+ ion is completely isolated from neighboring Eu 2+ ions by being surrounded with that network. The con- centration quenching effect in this borate is expected to be small compared with the other Eu(II)-borates. Therefore the haloborates

TABLE 6

Luminescent data* for Eu(II)-borates

Compound I max (nm) Q. E. ( % )

Eu3B206

Eu2B205

EuB204 370 negligible

370 7 which have the similar values EuB407 of quantum efficiency to that of EuB407 must be also the *See Ref.(3). structures in which Eu 2+ ions hardly interact with the neighboring Eu 2+ ions. The emission peak positions of Eu(II)-phosphors are largely affected by the crystal fields formed by neighboring anions. The difference between the peak positions of Eu(II)-borates and Eu(II)-haloborates suggests that the anion environments around Eu 2+ ions in them differ from one another.

1534 K. MACHIDA, et al. Vol. 14, No. 12

i.

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Acknowledgement

We wish to thank Mr. K. Tomokiyo for his assistance.

References

H. Hata, G. Adachi and J. Shiokawa, Mat. Res. Bull., 12, 811 (1977).

K. Machida, H. Hata, K. Okuno, G. Adachi and J. Shiokawa, J. Inorg. Nucl. Chem., in press.

K. Machida, G. Adachi and J. Shiokawa, J. Luminescence, in press.

T. E. Peters and J. Baglio, J. Inorg. Nucl. Chem., 32, 1089 (1970).