Polarized vibrational, electron absorption and luminescence spectra of Nd(NO3)3(DMSO)4 single crystal

Specrrochimico Acu, Vol. 42A, No. Printed in Great Britain.

10, pp. 1089-1099,

1986.

0584-8539/86 S3.00+0.00 Pergamon Journals Ltd.

Polarized vibrational, electron absorption and luminescence spectra of Nd(NO,),(DMSO), single crystal J. HANK& K. HERMANO~ICZand Z. MAZURAK Institute for Low Temperatures and Structure Research,Polish Academyof Sciences,Wroclaw, Poland and Institute of Chemistry, Wroclaw University, Poland (Received 22 May 1985; infinal form 10 March 1986; accepted 20 March 1986)

AbstrnceInfrared and Raman spectra of polycrystalline and single crystal Nd(NO,),(DMSO), have been measured.The molecular and crystal structure is analysed in terms of a monoclinic unit cell of C2/c symmetry. A comparison of i.r. spectra measured parallel and perpendicular to the b axis of the unit cell as wellas Raman spectra for severaltensor elements was used to describe the internal and external optical modes. The optical absorption and luminescence spectra of neodymium nitrate tetra dimethyl sulphoxide single crystal were recorded at 77 and 3COK between 4000-30000 cm-‘. The electronic transitions were assigned to the crystal field splitting manifolds. The band intensity measurements performed for (1and _Lb polarizations are related to Judd-Ofeld parameters and the anisotropy of these values is discussed.

INTRODUCTION Dimethyl sulphoxide complexes of transition and non-transition metal compounds have been studied by several authors [l-l 11. Single crystal X-ray diffraction studies have established the structures of the following complexes of lanthanide nitrates: La(NO3)3(DMSOk CW,NdWhWMs0)4 C131, Er(N03)3(DMW3 [141, YWW3PMW3 Cl51 and Lu(NO,),(DMSO), [16]. In all cases, the coordination of DMSO through the oxygen was confirmed, but the nitrate groups were found to be bidentate in contradiction to earlier suggestions based on i.r. evidence [7] that only one is likely to be bidentate. The i.r. and Raman studies of these lanthanide complexes were performed for the polycrystalline state only [7, lo]. In this work experimental results of i.r. Raman, electronic absorption and luminescence studies for a Nd(N03)3(DMSO)d single crystal are reported. The optical properties of this material are of particular interest because these compounds seem to be promising laser materials. EXPERIMENTAL The Nd(N03),@MSO), complex was prepared according to the method described in [7]. The single crystal suitable for optical measurements was grown at room temperature by controlled evaporation of a saturated methanol solution. The identification of the compound was inferred from chemical Lanalysis. The orientation of the crystal was performed using the X-ray method. The optical axes were determined using a polarization microscope. Polarized i.r. transmittance spectra were recorded on a Perkin-Elmer 180 spectrophotometer with polyethylene and AgBr polarizers. The near i.r. spectra in the 400-5000 cm-’ region were measured on a UR 20 Zeiss Jena spectrophotometer without polarization. The Raman &ectra were measured in the 5-4OOOcm-’ region on a JEOL spectrometer. The 4880 and 5145 A argon laser lines were used for excitation at a power of 500mW. The absorption spectra were recorded on a Cary 14 spectrophotometer and the fluorescence measurements at 77 and 300 K in a spectrophotometer designed in our laboratory

using a Carl Zeiss GDM IO00 grating monochromator and a phase-sensitive detection system with a photomultiplier of S-l response. The luminescence was excited by a ILA 120 argon laser (1,,, = 4880 A).

RESULTS AND DISCUSSION 1. Unit cell vibrational analysis-infrared spectra

and Raman

From single crystal X-ray data Nd(N03)3(DMS0)4 is monoclinic with a C2/c (C$,) space group. The parameters of the monoclinic unit cell are as follows: a = 14.95 A, b = 11.02 A, c = 15.50 A, B = 108.2”, Z = 4.The crystals are elongated along the c axis. The primitive unit cell is built from two molecules of Nd(NO,),(DMSO), which occupy position e on the two-fold symmetry axes. The NdO,,, coordination polyhedron has C, symmetry, being formed from four oxygen atoms of DMSO and six oxygen atoms of three bidentate nitrate groups. A sketch of the neodymium+xygen coordination polyhedron is presented in Fig. 1. Table 1 summarizes the factor group predictions. Phonons with even symmetries are Raman active but i.r. inactive and those with a, and b, symmetries are i.r. active but Raman inactive. The alp b, a, and b, spectra correspond to the unit cell modes and were measured with the following polarizations: a, modes, c*(bb)a, a(bb)c*, b(c*c*)a; b, modes, ~*@*)a, c*(bc*)u, a(ba)c*; a, modes, 11b axis and b, modes I b axis, since the b axis of the unit cell coincides with the optical Y axis. Figures 2-7 illustrate the i.r. and Raman

spectra for representative polarizations and scattering geometries. The band frequencies and assignments are summarized in Table 2. 1.a. Internal vibrations of coordinated DMSO. The i.r. and Raman spectra for all DMSO-containing complexes are basically similar regarding the coordinated DMSO-vibrational modes, with the exception of the bands corresponding to the S(CS0) modes. The fundamental vibrations of coordinated DMSO were

1089

J.

HANUZA et al.

Fig. 1. Sketch of the NdO,, coordination polyhedron.

Table 1. The unit cell vibrational analysis for Nd(NO,),

(DMSO),

crystal

Unit cell modes E

vR

uR(s)

U,(s-p) Ex,Wh p,‘r tipCR)lr P R

106

201b)

6

i

0

n(N) n(T) 4T’)

44

n (int)

n(R)

Infrared

a#

78

0

11

10

57

{4;;;;o}

-

b,

81’

0

13

11

57

{4g!;;o}

-

a”

78

1

10

10

57

{4::~;o}

b,

81

2

11

11

57

{4;;;;o

318 ;;ji;8

3

45

Activity Raman xx,

w,zz,xz

xu, E

0

16

4

0

0

143 318 42 45

-2 -3 -6 2 -1

-3 03

y0

assigned by comparison with the data reported for the free ligand [ 17-201 and some d- and f-electron metal complexes [l-l 11. The results obtained here for the -CH, group vibrations are consistent with the literature data [17-201. The polarization behaviour of these bands depends on the nature of the normal mode. As expected, perceptible differences are observed only for symmetric modes where e.g. for the bands at 2920 cm-’ relative intensities of the a, and b, spectra differ by 40x, for 6,(CH,) modes at 1320cm-’ by SO%, for p .(CH,) modes at 1025 cn-’ by 100% and Q(CH,) at 940cm-’ by 80%. For the dipole induced modes a, and b, the CH, vibrations are relatively only slightly polarizable. The intense band occuring at about 1045cm-’ attributable to the S-O stretch in free DMSO [17-201 shifts to 1002-1005 cm-’ in thecomplex under investi-

}

y

-

x,z

-

gation. This frequency shift during coordination of the ligand is consistent with the linking of DMSO through the oxygen atom [l, 2,7]. Our assignment of v(S0) in the range 100&1005 cm -r is in agreement with the results of several authors who have investigated other lanthanide DMSO complexes in the polycrystalline state [7-lo]. These band intensities are not sensitive to polarization changes. The SO bands in an elementary cell are oriented in such a way (Fig. 1) that the sums of the squared projections with respect to axes ]I and I6 are almost equal, i.e. the i.r. band intensities for the a, and b, spectra should be comparable, as observed. The bands in the regions 71&715 and 665_682cm-’ were assigned to the v,(CSC) and v,(CSC) modes, respectively [7, lo]. They are highly polarized. Their intensities for the a, and a, spectra are two or three times stronger than those of the b, and b, spectra. Similar behaviour is shown by the S(CS0) and

Spectra of Nd(NO,),@MSO),

single crystal

Fig. 2. The a,-c*(bb)a Raman spectrum of the Nd(N03)3(DMS0)4 range.

single crystal in the 3Ck4000cm-’

Fig. 3. The b,-c*(bc*)a Raman spectrum of the Nd(NO,),(DMSO), range.

single crystal in the 3C4000 cm-’

y(CS0) modes which have bands appearing over the 400-416 and 345-358 cm-’ regions, respectively. The S(CSC) bending modes absorb i.r. radiation over the 314318cm-’ range [7, lo]. Like other skeletal bending vibrations these modes are shifted from 308 cm- ’ to a higher frequency region upon coordination through the oxygen atom. These band intensities are not sensitive to polarization changes. It should be emphasized that measurements of the polarized vibrational spectra reveal in many cases a splitting of the band observed. The C, crystal axis through the molecule divides four DMSO ligands into two pairs of equivalent sets. Similar behaviour is

1091

by the nitrate ligand where the C1 axis makes two equivalent groups while the third is different. This structural non-equivalence of the ligands should lead to band splittings, as observed. 1.b. Internal vibrations of nitrate ligands. The vibrational bands due to the nitrate groups were identified by comparison with the spectra of corresponding anhydrous rare earth nitrates [21-281. The results are consistent with an environment involving coordinated bidentate chelated nitrates around the lanthanide metal. On the basis of the literature evidence and polarization behaviour one could classify particular vibrational modes for the bidentate chelated nitrate shown

J. HANUZAet al.

1092

Fig. 4. The a,-c*(bb)a (solid line) and b,-c*(bc*)a (dashed line) Raman spectra of the Nd(NO,),(DMSO), single crystal in the 5OCk1500cm-’ range.

250 Fig. 5. The a,a(bb)c*

Cdl

(solid line) and b,a(ba)c* (dashed line) Raman spectra of the Nd(NO,),(DMSO), single crystal in the 3&5OOcm- range.

ligand and assign their absorption ranges. Fundamental, combination and overtone frequencies of these vibrations for lanthanide complexes lie in the energy ranges listed in Table 3, where the results obtained for Nd(NOJJ(DMSO), are compared. The nomenclature used for the assignment of the normal modes and of their combinations is in accordance with C,, local symmetry for the bidentate nitrate group [21,22,26]. The very strong i.r. bands at 1455(a,) and 1459(b,) and the polarized weak Raman lines at 1455(a,) and 1460(b,) are assigned to the v1 mode of the bidentate nitrate ligand [21,22,26]. Since these bands correspond to the C,, symmetry A, species they should be

polarized in Raman spectra. FERRARO et al. [29] have measured the Raman spectrum of Th(NO,),(TBP), (TBP = tributyl phosphate) and have concluded that all the nitrate groups in this compound act as bidentate ligands, since the line at ca 15OOcm-’ is polarized. Therefore a Raman polarization study may provide a tool for distinguishing unidentate from bidentate coordination. The adjacent bands at 1420 (a,, b,) cm - ’ (Table 2) are not polarized so they correspond to the 6, (CH,) modes. Very strong Raman lines at ca 1045 (a,) and 1043 (b,) cm-’ correspond to v2 modes of the nitrate ligand. These bands are strongest in the Raman spectra and also strongly polarized. Their corresponding i.r. ab-

Spectra of Nd(NO,),@MSO),

single crystal

1093

Fig. 6. The a,(11b) (solid 1ine)andb,( I b) (dashed line) i.r. spectra of the Nd(NO,),(DMSO), the 2oo-4ooocm-’ range.

single crystal in

.’

‘\

.’ ‘X._./

Fig. 7. The polycrystalline (pointed line), a,(l(b) (solid line) and &( Lb) (dashed line) ix. spectrum of the Nd(NO,),(DMSO), single crystal in the 40-5OOcn1-~ range.

sorptions are weak and masked by strong v(S=O) and p(CH,) bands. The doublet at 732-738cm-’ (b, spectrum) and singlets 735(a3,740 (up b,) correspond to vj modes. The intensities of these bands depend on polarization to a similar extent as those for other modes of bidentate nitrate groups. The i.r. multiplet at 1295-1335 cm-’ is assigned to the vq mode accidentally degenerate with one of the G,(CHs) components. In the Raman spectra they are absent and only one band in this region corresponds to 6,(CH,). The v5 mode of the bidentate NO; group is expected to absorb near 71Ocm-‘. The bands observed near this frequency may be, however, assigned to v,(CSC) and also to v,(N03). The relative intensities of these bands are much stronger for the crystal than for powders; they depend also on the polarization of light. It seems that these bands apply to v,(CSC) since, as a rule, the v,(NO,) modes correspond either to low intensity bands or are not

observed [25]. The doublet of strong intensity at 818 and 833cm-’ observed in a, and b, spectra corresponds to the vs(NOB) modes [21-281. These bands are not observed in the Raman spectra. Apart from the above bands characteristic of the bidentate NO, ligand, the i.r. and Raman spectra contain a very complex multiplet attributed to the twophonon lines. These bands are usually observed in the spectra of solid nitrate compounds [21-281. l.c. Neodymium-oxygen modes. The neodymium atom lies inside a polyhedron with 10 vertices, four of which are oxygen atoms of the DMSO ligand while the other six are oxygen atoms of the three bidentate NO, groups (Fig. 1).The Nd-0 distances between the metal and oxygen for the DMSO ligands are 2.36-2.38A while for the nitrate groups the distance is 2.60-2.73 A [13], i.e. the distance for DMSO is significantly shorter. We can therefore expect that the Nd-O,,so stretching frequencies will be higher than the Nd-ONo,

1094

J. HANUZA et al. Table 2. The a,, b,, a# and b, phonons b,

2940 w 2905 m 2838 VW 2800 VW 2770 sh 2730 sh 2610 sh 2585 VW 2495 sh 2475 w 2450 w 2370 w 2350 w 2320 m 2280 VW 2230 VW 2200 VW 2165 sh 2140vw 2075 VW 2025 w 1995 sh 1964w 1928 VW

3925 VW 3840 VW 3700 VW 3400 VW 3315 VW 3260 VW 3005 m 2995 m 2940 sh 2910m 2840 VW 2810 sh 2770 sh 2730 sh 2610 VW 2590 VW 2495 sh 2470 w 2450 sh 2370 VW 2350 w 2330 w 2280 VW 2230 VW 2200 VW 2170 sh 2140 VW 2080 VW 2025 w 1995 sh 1965 sh 1928 VW

2000w 1890~~ 1855 VW 1770 VW l742m 1711 VW

2c0Ow 1885 VW 1855 VW 1770m 1745 w 1712 VW

3925 3840 3700 3400 3320 3260

VW VW VW VW VW VW

3000m

1455 vs 1410 vs 1378 vs 1332 vs 1310 sh 1290 sh 1080 sh 106Osh 1002 1021 966 945 910 833 818

s sh s m m s s

735 s 712 s 708 s 700 sh 677 w 665 w 648 VW 530 sh 468 sh 454 VW 410 s 400m

1459 vs 1410 sh 1378 vs 1335 vs 1315 sh 1295 sh 1080 sh 1065 sh 1040 sh 1005 s 1030 s 965 s 945 m 910m 833 s 818 s 738 s 732 s 714 s 710s 700 sh 677 w 665 w 648 VW 465 sh 454 VW 416 s 400m

of Nd(NO,),(DMSO),

Assignment

b,

Two-phonon 3010 (4) 2920

(13)

single crystal

transitions

(CH,)

3010 (4)

“a,

2920 (8)

v, WJ Two-phonon

transitions

2750 (1.4)

2750 (2.2)

Y, + v., of the nitrate

2600 (2)

2600 (2.5)

2 x Ye of the nitrate

2500 (2)

2500 (2.5)

vI + vz of the nitrate ligands Two-phonon transitions vr + Ye of the nitrate ligands

vt + vq of the nitrate Two-phonon

2150 (2) 2000 (1.5)

2150 (2.5) 2000 (2.2)

1750 (0.4)

1740 (0.4)

vI + vs of the nitrate 2 x v(S=O)

ligands

ligands

transitions

v2 + vj of the nitrate v2 + vs of the nitrate

1710 (0.4)

ligands

transitions

Two-phonon

1825 (0.4)

ligands

1640 (0.4) 1455 (0.8)

1640 (0.4) 1460 (0.8)

2 x vg of the nitrate

1420 (3.3)

1420 (2.4)

6, (CH,)

1320 (1.7)

1320 (0.4)

&(CH3)

ligands ligands ligands

VI(NW

vd(NW Two-phonon 1045 1005 1025 970 940

(100) (6.5) (1Oj (4) (1.4)

1043 (20) 1005 (6.5)

.

transitions

v,(NW v(S=O)

’

970 (4) 940 (0.4)

PW,) v,(NW

740 (8)

740 (2.6)

v,(NW

715 (46)

715 (20)

v,,(CSC) and/or

682 (49) 675 sh

682 (24) 675 sh

v,(CW Two-phonon

540 (0.4) 470 sh 406 (14.5)

408 (3)

YSO) 912

v,(NOs)

transitions

Spectra of Nd(NOs)s@MSO), single crystal

1095

Table 2. (Continued)

b,

% 370 vw 355 s 345 s 330 sh 314 m 310 m, sh 276 m 265 m 228 w 214m 206m 196 m 186m 178m 166m 154w 152~ 142~ 16Om 134vw 1OOvW 88wi

4

369 sh 358 s 330 sh 314 s 310 m, sh 276 m 265 m 228 m 214m 206m 196 m 189 m 175 m 166 m 154w 152m 142~ 160m 134vw 198 w 88 w 67vw

Assignment

4

375 sh 352 (13)

354 (8)

Y

318 (6.5)

318 (13)

6(CSC)

tcw

%,2

225 sh

235 sh

193 (6.3)

193 (2)

v(NWxmo)

156 sh

156 sh

“@d-ONoJ

4kV2 120 (13) 77 (2.5) 50 sh

117 (14.5) 77 (9) 50 sh

R modes

Table 3. The vibrational modes for bidentate chelated nitrate ligand

Vibrational mode

Vibration frequency for lanthanide nitrate complexes \21-281 (cm- )

Vibrational frequencies observed for Nd(NO,),(DMSO), crystal in the present study a, b, % b0

145~1510 1030-1050

1455 1045

1460 1043

V3

730-755

740

740

V4 VS

1280-1300 700-725

Vl Vt

715

715

2500

2500

vz+v3

2040-2080 25W2540 2290-2350 1750-1770

1750

1740

v2+v5

1730-1745

1710

2v6

1620-1680

1640

1640

2v4

2580-2630

2600

2600

v,+v4

2730-2770

2750

2750

v6 32 v1+vz v2+v4

810-840

stretching vibrations. Since the NdOio polyhedron has C2 symmetry all the Nd-0 vibration modes are i.r. and Raman active and interactions of the two primitive cell molecules cause each of the a, b,, a,, b, spectra to contain two multiplets with four and six bands for the v (Nd-O,& and v (Nd-ONo,) modes, respectively. A description of the vibrational spectra over this energy region is difficult due to the fact that the dipole mechanism of transitions between the Stark components of the ground 419,2 level also activates electronic transitions. However, comparison of the vibra-

1455 735

1459 1040 738 732 1295 710 833 818 -

1290 708 833 818 2495 2320 1770 1742 1711

2330 1770 1745 1712

2610 2585 2770 2730

2610 2590 2770 2730

tional spectra with 4F,,, + 41,,, luminescence at 300 and 77 K enables us to separate electronic transitions from the vibrational ones. The four Stark components of the 41,,2 level are observed in the i.r. spectra at 160, 265, 310 and 4OOcrn-‘. The other far i.r. bands correspond to translation T’(Nd’ ‘) modes which are identified in many papers with the neodymiumoxygen stretching vibrations [lo, 241. In the i.r. spectra of polycrystalline Nd(NO,),(DMSO), these modes correspond to a very strong and. 14Ocm- ’ broad absorption with a maximum at 187cm-’ and a

J. HANUZAet al.

1096

shoulder at about 155cm-’ (Fig. 7). In the a” and b, spectra of the crystal a multiplet consisting of 10 bands occurs in this place. Four bands lie at about 142, 152, 154 and 166cm-’ and the next six bands at 178, 189, 196, 206, 214 and 228cm-‘. All these bands are assigned to the translation modes T’ (Nd3+ )-the first four bands correspond mainly to the stretching v(Nd+O,N) vibrations [24] and the other six to v(Nd-O,,so) [lo]. The centres of gravity for these two multiplets occur at the absorption maxima observed in the spectra of polycrystalline samples. Other far i.r. bands found below llOcm_’ result from 6(ONdO) bending vibrations and may be considered to be lattice R(NdO,,) rotational vibrations.

2. Electronic

absorption

and luminescence

spectra

2.a. Electronic absorption spectra and anisotropy The sequence of 4f3 energy levels for Nd3+ in the solid state is easily obtained by optical absorption and luminescence techniques at room and low temperatures. Valuable results can be also obtained from studies of oriented crystals in polarized light. A number ofcompounds have been investigated since the early measurements of DIECKE [29]. Nd3+ ions in cubic and biaxial crystals have been studied by several authors [30-343. The present work reports the polarized absorption and luminescence spectra of Nd(N03)3(DMSO)c oriented crystals up to 30OOOcm-‘. The optical absorption spectra measured in light polarized parallel and perpendicular to the b axis of the unit cell are shown in Fig. 8. The energy levels of Nd3+ m the crystal under investigation are listed in Table 4.

factors.

In order to evaluate the effect of crystal anisotropy on the values of oscillator strengths, an analysis of the intensities of thef-ftransitions was carried out. In the present work the method introduced by JL’DDOFELT [35] and modified by CARNALL et al. [36] was used. The Nd3+ ion concentration in the crystal was estimated to be 4.0Mjdm3. The oscillator strengths P were determined numerically by integrating the areas below the absorption contour. The TVparameters were determined by minimization of ZAP. The results of these calculations are presented in Tables 5 and 6. 2.b. Luminescence spectra. Numerous papers on the fluorescence properties of neodymium containing materiais can be found in the literature. However, our knowledge of physical processes governing the fluorescence quenching is still insufficient. The discovery of stoichiometric neodymium crystals which exhibit a laser emission [37] offers many interesting possibilities. In Figs 9 and 10 the appropriate spectra of 4F3,,, 4 + 41,,2 and F,:, ---)41 11j2 transitions at 300 and 77 K are reproduced. The discussion and assignment of 4F3,2 + 41, 1:2 luminescence to the induced transitions are presented in Fig. 10. A decrease in the luminescence temperature down to 77K considerably improves its quantum yield. This is related to a decrease in the speed of multiphonon transitions in the crystal. Owing to the presence of v(C-H) vibrations in the i.r. light absorption the maximum phonon energies reach a value of 3OOOcm- ’ and the energy difference between the 4F3 ,z and 411112levels is about 9OOOcm -I. The assignment of luminescence based on these levels as suggested in this paper allows us to describe the electronic levels in the Nd3+ ion in the crystal under investigation. We

Fig. 8. The electronic absorption spectra of the Nd(NO,),(DMSO), single crystal polarized line) and perpendicular (dashed line) to the b axis of the unit cell.

parallel (solid

Spectra of Nd(NO,),(DMSO),

single crystal

Table 4. Energy levels of Nd 3c in Nd(NO,)s(DMSO), Nominal state

Stark level positions at 290 K

411112 411312 41 l3,Z 4F3,* 4F3,*

+

*Kv*

*F,,* 4s3,* 4Fw*

*H,112 4G,,* *G,,* 4G,* %v* *r-c 1312

*%z *D3,*

4G I112 *K 15,* *PI,* *D,,* *p3,* 4D3,* 4D,,* 4D~,* *I

II,2

*LIS,2 4D,,*, ‘1131,

crystal

Number of components Theor. Exp.

(cm-‘)

419,*

1097

0,160,265,310,400 1928,1965,1990,2025,2080,2140 3840,3937,3949,4013,4043 5106, 5190, 5865, 5941, 5963, 5993, 6006,6024 11360,11510 12 160, 12 345, 12430,12 520,12 560,12 780 13200,13270,13400,13580 13480,135lO 14 410,14 720,14 745,14 785,14840 15650,15800,15910,15945,16035,16080 17 250,17 140,16850 16980,17000,17205,17420 18870,19000,19300,19 160 19400,19520,19570,19600 19600-19850

5 6 7 8 2 8 4 2 5 6 3 4 4 5 1

21060,21220 21400 21680 21750 23 310 23 830 26100 28 080, 28 190 28 280,28 340,28 460 28 690 29 100-29 600 30040-30200 30200-30700

5 2 6 8 1 3 2 2 3

5 6 5 8 2 6 4 2 5 6 3 4 4 4 Very broad Weak shoulder 2 Broad line vb line vb line 1 w, b line w, b line 2 3

:, 8 11

:b VW,b sh vb

Charge transfer Nd ; ligand 35cQO

vs, b line

Table 5. Experimental and calculated oscillator Nd (NOs),(DMS% Spectral range Level

(nm)

4Fwz

*Jh 4F,,z

4Ss/z,

4F,,z 4Fwz 2HII/Z 4%* *G,* *K13,* 4G,,* 4%* *K1512 *Gw* *D3,*,

850-910 111-833 711-767 665-702 62-7 565603 501-540

454482

*F3,*

4G 1112 *PI,* *L’s,* 4Dw* 21II,2 *D,,*

*L1512

cannot,

427-436

362-345

strengths for

Pexpxlo6 %ax (cm-‘) 11495 12500 13513 14705 15 936 17 150 17452 18 885 19047 19 510 20920 21097 21250 21762 23015 23 331 28 129 28 368 28 135

however, analyse 4F,,,+ 41,,, luminescence in a similar manner, since this spectrum is more complex than would appear from the diagrams of Stark splittings of both levels or the crystal structure

direction Ib lib

Nd3+

ions

in

P&X lo6 direction UJ

lib

1.095 4.313 4.529 0.407 0.101

1.194 4.523 4.932 0.427 0.099

1.399 4.423 4.558 0.358 0.099

1.458 4.685 4.841 0.381 0.105

13.273

15.822

13.294

15.834

3.820

4.005

3.519

3.825

0.818

O.-Ill

0.770

0.811

0.100

0.108

0.376

0.390

3.110

4.006

3.157

3.913

model. Eleven distinct nescence spectrum band described by transitions brational components of

components of the lumimeasured at 77K may be from the 4F3,, level to vithe ground state or by as-

J. HANUZAet al.

1098

6-

5 &F 32

‘I

92

L-

Fig. 9. The “Fgi2 + 41,,,

luminescence spectra of single Nd(NOs),(DMSO), (solid line) and 77 K (dashed line).

crystal

measured

at 300K

2-

IO.I1 360

8.

‘6.

- 2160 2.

2080 ~2025

95co

Fig. 10. The 4F,,,

-+ 41,,,,

-

V [cm-‘]

-

luminescence spectra of the single Nd(NO&(DMSO), 300 K (solid line) and 77 K (dashed

suming the presence of two different sites for the neodymium atom. Further studies, especially spectral measurements at liquid helium temperature, should determine which of these mechanisms is relevant. Determination of the experimental oscillator strengths for the two fundamental optical directions 11 and I to the 6 axis of the monoclinic crystal enables us to evaluate the effect of anisotropy on the accuracy of

crystal

1995 1965 1928

measured

at

line).

the 7i parameter determination. Experimental data (Table 5) show that a change in oscillator strengths for both polarizations ranges from 9% for the 419,2 --t 4F,,Z transitions up to 25 % for the hypersensitive transition 4Z,,, --* 4G,,,, ‘G,,,. The relationship found is consistent with that predicted theoretically by MASON et al. [38] who related changes in the values of electron transition oscillator forces with changes in

Spectra of Nd(NO,),@MSO),

1099

single crystal

Table 6. The calculated r2, T,, ~c intensity parameters for the Nd3+ ion in Nd(NO,),(DMSO), crystal

Direction Lb llh Calculated for P=

Plb+Pllb

2

rz x log

Parameter r* x log

T6 x lo9

4.78kO.16 6.11 kO.15

4.15f0.20 4.3OkO.19

4.82 f 0.18 5.13*0.17

5.40*0.15

4.2OkO.19

5.00* 0.17

[14] L. A. A. ASLANOV, L. J. SOLEVAand M. A. PORAIKOSHITS,Zh. Struct. Khim. 13, 1021 (1972). [15] K. K. BHANDARY,H. MANOHARand K. VENKATESAN, J. them. Sot. Dalton Trans. 288 (1975). [ 161 L. A. ASLANOV,L. J. SOLEVAand M. A. PORAI-KOSHITS, J. Struct. Chem. 14, 988 (1973). [17] W. D. HORROKS,JR and F. A. COTTON, Spcctrochim. Acta 17, 134 (1961). r181 M. T. FORELand M. TRANQLJILLE, Spectrochim Acta. 26A, 1023 (1970). fl91 M. TRANOUILLE. P. LABARBE.M. EQUASSIER and M. T. FOREL, J:mclec: Struct. 8, 273 (1971). [20] G. GEISELER and G. HANISCHMANN, J. molec. Struct. 8, 293 (1972). r211 D. G. HENDRICKER and R. J. FOSTER,J. inorg. nucl. Chcm. 34, 1949 (1972). r221 R. L. DIECKand T. MOELLER,J. inorg. nucl. Chem. 36, .a 2283 (1974). [23] C. C. ADDISON,N. LOOAN, S. C. WALLWORKand C. D. REFERENCES GARNER,Q. Rev. 25, 289 (1971). [24] J. R. FERRAROand A. WALKER,J. them. Phys. 42,1273 (1965); 43, 2689 (1965). [1] F. A. OXTON and R. FRANCIS,J. Am. them. Sot. 82, [25] G. CASXTO, B. ZARLI, G. FARAGLIA and L. 2986 (1960). SINDELLARI, Inorg. chim. Acta 95, 247 (1984). r21 .._ D. W. MEEK, D. K. STRAUBand R. S. DRAGO, J. Am. [26] J. I. BULLOK,J. inorg. nucl. Chem. 29, 2257 (1967). Chem. Sot. 82,6013 (1960). [27] G. TOPPING,Spcctrochim. Acta 21, 1743 (1965). f31 J. SELBIN.W. E. BULLand L. H. HOLMES.J. inora. nucl. [28] R. GRAZIANI,G. BOMBIERI,E. FORSELLINI, S. DEGETTO L d Chem. 16; 219 (1961). and G. MARANWNI, J. them. Sot. Dalton Trans. 451 [4] V. KRISHNANand C. C. PATEL,J. inorg. nucl. Chem. 26, (1973). 2201 (1964). [29] G. H. DIEKE, Spectra and Energy Levels RE Ions in f51 H. Lux, L. EBERLEand D. SARRE,Chcm. Ber. 97, 503 Crystals. Interscience, New York (1968). - - (1964). \-- iI61D. G. HOLAHand J. P. FACKLER.JR.. Inora._ Chem. 4, c301T. S. LOMHEINand L. G. DE SHAZER,Phys. Rev. B20, 4343 (1979). 1721 (1965). PI S. K. RAMALINGAMand S. SOUNDARAJAN,Curr. Sci. C3’1 P. CA~O, c. R. SVORONOS,E. ANTICand M. QUARTON, J. them. Phys. 66,5284 (1977). India 35, 233 (1966); J. inorg. mud. Chem. 29, 1763 and P. N. SCHATZ,Phys. Rev. B&3229 (1967); V. N. KRISHNAMURTHY and S. SOUNDARAJAN, J. [32] R. W. SCHWARTZ (1973); R. W. SCHWARTZ,Molec. Phys. 30.81 (1975); 31, inora. nucl. Chem. 29.517 (1967). 1909 (1976). PI K. -KRISHNA BHAN~ARY,’ H. ’ MANOHAR and K. VANKATESAN, J. inorg. nucl. Chem. 37, 1997 (1975). c331 A. A. KAMINSKII,H. D. KUR~TENand D. SCHULTZE, Phys. Stat. Sol. 81, K19 (1984); 72, 207 (1982); A. A. c91B. R. JAMES~~~R. M. MORRIS,Spectrochim. Acta 34A, KAMINSKII, Luscr CrystalwTheir Physics and 577 (1978). Properties. Springer, Be& (1981). Cl01Y. KAWANOand V. K. LAKATOSOSORIO,J. inorg. nucl. H. D. AMBERGER.Spcctrcchim. Acta 34A, 627 (1978). chcm. 39,701 (1977). G. S. OFELT, J. &em. Phys. 17, 511 (1962). [:I Cl11 A. IWASE and S. TADA, Nippon Kagaku Kaishi 60 (1973). 1361W. T. CARNAL, P. R. FIELDSand B. G. WYBOURNE, J. them. Phys. 42. 3797 (1965). PI K. K. BHANDARYand H. MANOHAR,Acta crystallogr. G. HUBER,Current Topics Mat. Sci. 4, (1980). 29, 1093 (1973). S. F. MASON, R. D. PEACOCKand B. STEWART,Molec. Cl31L. A. ASLANOV.L. J. SOLEVA.M. A. PORAI-KOSHITS Phys. 30, 1829 (1975). and S. S. GOUK~BERG,Zh. S&kc. Khim. 13,655 (1972).

polarixability. According to that theory, the largest changes related to a change in ligand polarizabilities should be observed for hypersensitive transitions. The results of the present work indicate quite clearly that crystal anisotropy affects very significantly the error of determination for the r1 parameters (Table 6). This parameter is (4.78 f0.16) x 10m9 for the _l b direction and (6.11 +O.lS) x low9 for 11b, whereas that evaluated according to the Judd theory is (5.40+ 0.15) x 10m9. It is, therefore, advisable to apply more extensive polarized light in studies of the electronic spectra of crystals in order to allow for the effect of anisotropy on optical parameters particularly in monoclinic and triclinic crystals.

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