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Absorption spectrum of Nd3+:LiNH4SO4 single crystals
Volume
4, number
MATERIALS
2
ABSORPTION V. RAMESH Spectroscopic
Received
SPECTRUM BABU,
Laboratories.
7 November
OF Nd”+:LiNH,SO,
L. RAMA Department
MOORTHY
and
February
LETTERS
1986
SINGLE CRYSTALS S.
BUDDHUDU
of Physics. S. V. lJniaersit_y, Tirupari
517 501, India
1985
Light pink single crystals of Nd(III):LiNH,SO, have been grown under the slow evaporation method. The absorption spectrum of Nd(II1) crystal has been recorded in the UV-VIS and NIR regions. The energies and intensities of thirteen levels have been measured. By applying a least-squares fit analysis and Judd-Ofelt parametric procedures, a good fit between the experimental and theoretical energies and intensities for the Nd(lI1) ion has been obtained. Based on the magnitude of the bonding parameter for the ion studied, the bonding in the crystal lattice is suggested to be covalent. The evaluated spectroscopic parameters relating to the ion are reported.
The experimental values of the intensities served levels were obtained from [4]
1. Introduction Single crystals of Nd(II1) in LiNH4S04 have been grown by the slow evaporation technique for the first time in our laboratories. Previously, transition metal ions doped in LiNH4 SO4 were studied and interesting results were reported in the literature [ 1,2]. A good shaped crystal with appropriate dimensions has been chosen for the present work and the new results thus obtained are reported in this paper.
2. Experimental
studies
0.1 mole % of Nd2(S04),*8H20 was added to the equimolar concentrated solutions of lithium and ammonium sulphate. Then it was allowed to evaporate slowly at laboratory temperature to have Nd(III) single crystals. The absorption spectrum of this single crystal in the UV-VIS region has been measured with a Perkin-Elmer 55 1 recording spectrophotometer. The second-derivative spectrum of this crystal has also been recorded in the same wavelength region by using a derivative accessory to the spectrophotometer. The NIR spectrum was recorded on a Carl-Zeiss Specord 61 recording spectrophotometer. The refractive index value for the host lattice with Nd(III) has been obtained from the tables of Hodgman et al. [3]. 0 167-577x/86/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
for the ob-
f expt.= 4.32 X lo-’ [ e dv, where E is the band-width at coefficient (e) Beer-Lambert
extinction coefficient and dv is the half height. The value of the extinction is calculated for each band from the law [5]
e=A/CL, where C is the concentration of the ion in the crystal lattice ln moles/litre (in the present work C = 0.1 M%), L is the optical pathlength and A is the absorptivity.
3. Results and discussion 3.1. Electronic energy levels In the UV-VIS and NIR suectrum thirteen levels have been observed. These are4F3j2 ‘Hb,*, 4F7/2 g/2, 4G 5/2,1/2,9/2’ 2G 9123 2D,,2> 2P1,2,kD3/2 7,2 and’ *D&. The evaluation of the theoretical energies by a least-squares fit method [6] has been carried out on a DCM spectrum 3 1 minicomputer. The calculated and observed energies of these levels are presented in table 1. The evaluated Slater-Condon (F2, F4, F6), 99
Volume 4, number 2
MATERIALS LETTERS
February 1986
Table 1 Experimental and calculated energies of the observed bands of Nd(III):LiNH4S04 Transition from 4I9/2 (ground state) to
Eexpt. (cm-’ )
Ecalc. (cm-* )
+3/2
11200
11477
2Hb/2
12200
12480
'F7/2
13509
13455
4F9/2
14788
14739
4W2
17296
17107
4G7/2
19115
19160
4G912
19525
19344
2G9/2
21091
20873
2D3/2
21733
21434
---
23249
23224
4D312 2pl/2
28240
28277
4D7/2
30479
30527
2%/2
33435
33669
rms deviation ((I) = +-181 cm-l
, E2, E3), and spin-orbit (tf) parameters in table 2. The rms deviation of energy levels is computed from the formula [6] Racah (El
are presented
Table 2 Values of Slater-Condon (F2, Fq,F6),Racah (El,E2,E3), spin-orbit ([Jf), Judd-Ofelt (Th), refractive index (n) and intensity (S2,) parameters for Nd(III):LiNH4S04
-
~ F2
341.0512
F4
46.5360 5.7296
F6
5121.5536
El
3.2. Spectralintensities Theoretical estimates of the spectral intensities for the observed bands have been made following the method of Judd-Ofelt parameterisation [7,8], According to this
f talc.
= CT,v($Jll
vhll$‘J’)2,
where v is the energy of the transition $J+ G’S, @’ are the unit tensor operators of rank h, the sum running over the three values A = 2,4 and 6, T,, are the Judd-Ofelt parameters which are evaluated from the experimental data by a least-squares fit method. In the above equation the values of ($~JllL?ll $‘J’)2 are taken from the tables of Carnal1et al. for Nd(II1) free ion [9]. The observed and calculated spectral intensities are given in table 3, and the values of the JuddOfelt (T,) parameters, refractive index (n) and intensity parameters (8,) [7,8] are shown in table 2. Table 3 Experimental and computed spectral intensities of the observed bands for Nd(II1) : LiNH,SOa Transition from 419/2 (ground state) to
10’ fexpt.
105 fcalc.
0.4147
0.3890 0.3884
0.8087 0.8491
0.9246
E2
26.8389
0.0508
E3
487.6940
1.6703
0.2109 1.6552
885.3762 6.2137
0.2372 0.1961
0.5465 0.1163
n
7.4003 27.9681 1.5157
0.0931 0.0731 0.0468
0.5046 0.0338 0.0621
n2 (10’9) sz4 (1019) 526 (1019) 6
8.0376 9.5726 36.1778 0.3553
0.8132
t4f T2
(109)
j-4 (109) T6 (109)
100
Nd(II1) : LiNH4S04
Spectroscopic parameter
where Ai is the deviation of the level and N is the number of levels fitted.
0.5521 0.0765 0.2804 0.0389 0.0968 0 = r0.2140 x 1O-5
Volume 4, number 2
MATERIALS LETTERS
February 1986
3.3. Banking ~tur~
Ac~owl~gement
The evaluation of bonding parameter (8) for the ion studied has been carried out using the mathematical expressions given by Reisfeld [lo]. Since the bonding parameter (5) is taking a positive sign (as is seen from table 2) it has been suggested that the bonding nature is covalent. Similar observations have been reported earlier in the literature for various lanthanides in different hosts [l l-131.
We express our gratitude to Professor S.V.J. Lakshman for his help and constant encouragement during this research.
References Ill W.A. DoBase, Acta Cryst. 25 (1969) 2298. 121B.C.V. Reddy, J.L. Rao, K. Sudhakar and B. Munibhadraiah, Ferroelectric
4. Conclusions From tables 1 and 3 it is seen that there is good agreement between the experimental and computed energies and intensities of the observed levels. On comparing the energy level parameters given in table 2 with the free ion values [9], it is noted that there exists a significant improvement in the values of these parameters in the LiNH4S04 crystal lattice. The influence of the host lattice on Nd(II1) ion makes the characteristic intensity parameters of the ion to attain the following trend (table 2)
An attempt has also been made to understand the bonding nature of the ion from the energy values of thirteen observed levels reported in table 1 by measuring the ratio values with the aqueous ion energies
Letters 2 (1984) 147.
[31 CD. Hodgman, R.C. Weast and SM. Selsy, Handbook
of chemistry and physics (Chemical Rubber Co., Cleveland, 1959). 141 W.T. Carnal& H.M. Crosswhite and H. Crosswhite, Energy Level Structure and Transition Probabilities of Trivalent Lanthanides in LaFa, Argonne National Laboratories, Argonne, Illinois (1978). L51 LB. Scarborough, Numerical mathematical analysis (Oxford Univ. Press, London, 1968). [61 S.V.J. Lakshman and S. Buddhudu, Indian J. Pure Appl. Phys. 20 (1982) 667. 173 B.R. Judd, Phys. Rev. 127 (1962) 750. PI G.S. Ofelt, J. Chem. Phys. 37 (1962) 511. 191 M.J. Weber, J. Chem. Phys. 49 (1968) 4774. [lOI R. Reisfeld, Struct. Bonding 13 (1973) 53. P11 M. Jean-Louis and L. Couture, Chem. Phys. 33 (1981) 385. [121 H.M. Crosswbite, H. Crosswhite, F.W. Kuset and R. Sarup, J. Chem. Phys. 64 (1976) 1981. 831 V. Ramesh Babu and S. B~dhudu, Phys. Stat. Sol. b (1985), to be published.
101
4, number
MATERIALS
2
ABSORPTION V. RAMESH Spectroscopic
Received
SPECTRUM BABU,
Laboratories.
7 November
OF Nd”+:LiNH,SO,
L. RAMA Department
MOORTHY
and
February
LETTERS
1986
SINGLE CRYSTALS S.
BUDDHUDU
of Physics. S. V. lJniaersit_y, Tirupari
517 501, India
1985
Light pink single crystals of Nd(III):LiNH,SO, have been grown under the slow evaporation method. The absorption spectrum of Nd(II1) crystal has been recorded in the UV-VIS and NIR regions. The energies and intensities of thirteen levels have been measured. By applying a least-squares fit analysis and Judd-Ofelt parametric procedures, a good fit between the experimental and theoretical energies and intensities for the Nd(lI1) ion has been obtained. Based on the magnitude of the bonding parameter for the ion studied, the bonding in the crystal lattice is suggested to be covalent. The evaluated spectroscopic parameters relating to the ion are reported.
The experimental values of the intensities served levels were obtained from [4]
1. Introduction Single crystals of Nd(II1) in LiNH4S04 have been grown by the slow evaporation technique for the first time in our laboratories. Previously, transition metal ions doped in LiNH4 SO4 were studied and interesting results were reported in the literature [ 1,2]. A good shaped crystal with appropriate dimensions has been chosen for the present work and the new results thus obtained are reported in this paper.
2. Experimental
studies
0.1 mole % of Nd2(S04),*8H20 was added to the equimolar concentrated solutions of lithium and ammonium sulphate. Then it was allowed to evaporate slowly at laboratory temperature to have Nd(III) single crystals. The absorption spectrum of this single crystal in the UV-VIS region has been measured with a Perkin-Elmer 55 1 recording spectrophotometer. The second-derivative spectrum of this crystal has also been recorded in the same wavelength region by using a derivative accessory to the spectrophotometer. The NIR spectrum was recorded on a Carl-Zeiss Specord 61 recording spectrophotometer. The refractive index value for the host lattice with Nd(III) has been obtained from the tables of Hodgman et al. [3]. 0 167-577x/86/$ 03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
for the ob-
f expt.= 4.32 X lo-’ [ e dv, where E is the band-width at coefficient (e) Beer-Lambert
extinction coefficient and dv is the half height. The value of the extinction is calculated for each band from the law [5]
e=A/CL, where C is the concentration of the ion in the crystal lattice ln moles/litre (in the present work C = 0.1 M%), L is the optical pathlength and A is the absorptivity.
3. Results and discussion 3.1. Electronic energy levels In the UV-VIS and NIR suectrum thirteen levels have been observed. These are4F3j2 ‘Hb,*, 4F7/2 g/2, 4G 5/2,1/2,9/2’ 2G 9123 2D,,2> 2P1,2,kD3/2 7,2 and’ *D&. The evaluation of the theoretical energies by a least-squares fit method [6] has been carried out on a DCM spectrum 3 1 minicomputer. The calculated and observed energies of these levels are presented in table 1. The evaluated Slater-Condon (F2, F4, F6), 99
Volume 4, number 2
MATERIALS LETTERS
February 1986
Table 1 Experimental and calculated energies of the observed bands of Nd(III):LiNH4S04 Transition from 4I9/2 (ground state) to
Eexpt. (cm-’ )
Ecalc. (cm-* )
+3/2
11200
11477
2Hb/2
12200
12480
'F7/2
13509
13455
4F9/2
14788
14739
4W2
17296
17107
4G7/2
19115
19160
4G912
19525
19344
2G9/2
21091
20873
2D3/2
21733
21434
---
23249
23224
4D312 2pl/2
28240
28277
4D7/2
30479
30527
2%/2
33435
33669
rms deviation ((I) = +-181 cm-l
, E2, E3), and spin-orbit (tf) parameters in table 2. The rms deviation of energy levels is computed from the formula [6] Racah (El
are presented
Table 2 Values of Slater-Condon (F2, Fq,F6),Racah (El,E2,E3), spin-orbit ([Jf), Judd-Ofelt (Th), refractive index (n) and intensity (S2,) parameters for Nd(III):LiNH4S04
-
~ F2
341.0512
F4
46.5360 5.7296
F6
5121.5536
El
3.2. Spectralintensities Theoretical estimates of the spectral intensities for the observed bands have been made following the method of Judd-Ofelt parameterisation [7,8], According to this
f talc.
= CT,v($Jll
vhll$‘J’)2,
where v is the energy of the transition $J+ G’S, @’ are the unit tensor operators of rank h, the sum running over the three values A = 2,4 and 6, T,, are the Judd-Ofelt parameters which are evaluated from the experimental data by a least-squares fit method. In the above equation the values of ($~JllL?ll $‘J’)2 are taken from the tables of Carnal1et al. for Nd(II1) free ion [9]. The observed and calculated spectral intensities are given in table 3, and the values of the JuddOfelt (T,) parameters, refractive index (n) and intensity parameters (8,) [7,8] are shown in table 2. Table 3 Experimental and computed spectral intensities of the observed bands for Nd(II1) : LiNH,SOa Transition from 419/2 (ground state) to
10’ fexpt.
105 fcalc.
0.4147
0.3890 0.3884
0.8087 0.8491
0.9246
E2
26.8389
0.0508
E3
487.6940
1.6703
0.2109 1.6552
885.3762 6.2137
0.2372 0.1961
0.5465 0.1163
n
7.4003 27.9681 1.5157
0.0931 0.0731 0.0468
0.5046 0.0338 0.0621
n2 (10’9) sz4 (1019) 526 (1019) 6
8.0376 9.5726 36.1778 0.3553
0.8132
t4f T2
(109)
j-4 (109) T6 (109)
100
Nd(II1) : LiNH4S04
Spectroscopic parameter
where Ai is the deviation of the level and N is the number of levels fitted.
0.5521 0.0765 0.2804 0.0389 0.0968 0 = r0.2140 x 1O-5
Volume 4, number 2
MATERIALS LETTERS
February 1986
3.3. Banking ~tur~
Ac~owl~gement
The evaluation of bonding parameter (8) for the ion studied has been carried out using the mathematical expressions given by Reisfeld [lo]. Since the bonding parameter (5) is taking a positive sign (as is seen from table 2) it has been suggested that the bonding nature is covalent. Similar observations have been reported earlier in the literature for various lanthanides in different hosts [l l-131.
We express our gratitude to Professor S.V.J. Lakshman for his help and constant encouragement during this research.
References Ill W.A. DoBase, Acta Cryst. 25 (1969) 2298. 121B.C.V. Reddy, J.L. Rao, K. Sudhakar and B. Munibhadraiah, Ferroelectric
4. Conclusions From tables 1 and 3 it is seen that there is good agreement between the experimental and computed energies and intensities of the observed levels. On comparing the energy level parameters given in table 2 with the free ion values [9], it is noted that there exists a significant improvement in the values of these parameters in the LiNH4S04 crystal lattice. The influence of the host lattice on Nd(II1) ion makes the characteristic intensity parameters of the ion to attain the following trend (table 2)
An attempt has also been made to understand the bonding nature of the ion from the energy values of thirteen observed levels reported in table 1 by measuring the ratio values with the aqueous ion energies
Letters 2 (1984) 147.
[31 CD. Hodgman, R.C. Weast and SM. Selsy, Handbook
of chemistry and physics (Chemical Rubber Co., Cleveland, 1959). 141 W.T. Carnal& H.M. Crosswhite and H. Crosswhite, Energy Level Structure and Transition Probabilities of Trivalent Lanthanides in LaFa, Argonne National Laboratories, Argonne, Illinois (1978). L51 LB. Scarborough, Numerical mathematical analysis (Oxford Univ. Press, London, 1968). [61 S.V.J. Lakshman and S. Buddhudu, Indian J. Pure Appl. Phys. 20 (1982) 667. 173 B.R. Judd, Phys. Rev. 127 (1962) 750. PI G.S. Ofelt, J. Chem. Phys. 37 (1962) 511. 191 M.J. Weber, J. Chem. Phys. 49 (1968) 4774. [lOI R. Reisfeld, Struct. Bonding 13 (1973) 53. P11 M. Jean-Louis and L. Couture, Chem. Phys. 33 (1981) 385. [121 H.M. Crosswbite, H. Crosswhite, F.W. Kuset and R. Sarup, J. Chem. Phys. 64 (1976) 1981. 831 V. Ramesh Babu and S. B~dhudu, Phys. Stat. Sol. b (1985), to be published.
101