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Spectroscopic studies on Pr(III), Nd(III), Er(III) AND Tm(III) ions in fluoro-, boro-and acetophosphate glass environments
Journal of the Less-Common
Metals, 148 (1989)
357
357 - 361
SPECTROSCOPIC STUDIES ON Pr(III), Nd(III), Er(II1) AND Tm(II1) IONS IN FLUORO-, BORO- AND ACETOPHOSPHATE GLASS ENVIRONMENTS* A. SURESH
KUMAR
Department
of USIC, S. V. University, Tirupati - 517 502 (India)
S. V. J. LAKSHMAN Department (Received
of Physics, S. V. University, Tirupati - 517 502 (India)
June
8, 1988;
in revised form September
14, 1988)
Summary Spectral results of Pr(III), Nd(III), Er(III), Tm(II1) ions in fluoro (SFSP), boro (SBSP) and aceto (SASP) phosphate glass environments are reported. Spectroscopic parameters such as Racah, spin-orbit, configuration interaction and Judd-Ofelt intensity parameters have been evaluated. Lifetimes and branching ratios for certain lasing levels have been estimated. The splittings observed for certain bands in the second derivative spectra can be satisfactorily explained by superposition of the vibrational modes of the phosphate radical on the electronic bands.
1. Introduction Spectroscopic properties of ions depend strongly upon the environment of the laser ions with which they are surrounded [ 1,2]. Several tailoring techniques have been employed to alter the spectroscopic properties of rare earth ions in several media [ 3 - 51 to yield favourable situations for lasing action. The glass environments for rare earth ion laser action have certain advantages over their counterparts such as crystals, liquids and gases [ 61. Phosphate glass environments have indicated good laser action for certain rare earth ions [2, 3,7 - 91. In the present study, we have imposed fluoro-, boro- and acetophosphate glass environments on Pr3+, Nd3+, Er3+ and Tm3+ ions and evaluated the lifetimes and branching ratios for certain laser transitions.
*Paper presented at the September 12 - 16, 1988.
18th
Rare
Earth
Research
@ Elsevier
Conference,
Sequoia/Printed
Lake
Geneva,
WI,
in The Netherlands
358
2. Experimental details Good glass samples were prepared using the quenching method [lo]. One mol.% of rare earth (Pr, Nd, Er and Tm) ions was added in each of the glass composition shown below: sodium fluoride: sodium hexametaphosphate (SFSP), 70:29 sodium tetraborate: sodium hexametaphosphate (SBSP), 20: 39 sodium acetate : sodium hexametaphosphate (SASP), 30 : 69 Good glasses were formed at temperatures of 650, 750 and 750 “C respectively. Absorption spectra were recorded in the UV-VIS and near-IR regions on Perkin-Elmer 551 or Carl Zeiss Specord 61 spectrophotometers. The refractive indices of these glasses were measured using the “Becke line” method [ll]. The wavelengths of the bands were converted into vacuum wavenumbers using NBS wavenumber tables [ 121.
3. Results and discussion 3.1. Racah parameters The Racah (Ek), spin-orbit (&), configurational interaction ((Y, /3)and Judd-Ofelt intensity (a,, &, &) parameters derived from the spectral data are presented in Tables 1 and 2. From these tables it is noted that the ratios of E l/E3 and E 2/E3 are found to be nearly equal to 10 and 0.05 respectively for the four ions studied. This indicates that the radial properties are hydrogenie [ 131 and are unaffected by the environment.
TABLE
1
Spectroscopic
parameters
for Pr3+ and Nd3+ ions in three binary
glasses
Parameter
SFSP
Pr3+ SBSP
SASP
SFSP
Nd3+ SBSP
SASP
E’ (cm-‘)
4725.2 22.7 467.4 739.2 5.3 -457.02 8.80 1.31 7.06 1.492 312.2 10.11 0.05
4104.0 20.5 424.2 734.3 -53.3 802.6 6.32 1.31 8.21 1.492 278.6 9.67 0.05
4688.1 22.0 456.7 722.2 -2.8 -408.2 11,96 2.06 8.50 1.478 306.2 10.27 0.05
4909.5 26.1 503.0 860.8 5.0 -
5009.6
4883.5 26.3 500.9 876.7 4.6 -
EZ (cm-‘) E3 (cm-‘) t4f a
(cm+)
(cm-‘)
P (cm-‘) R,( XIOzo cm2) !i24( XIOzo cm2) Qj( XIOzo cm2) l2
El/E3 E2/E3
6.19 0.59 6.93 1.490 337.6 9.76 0.04
26.0 504.6 833.3 3.9 6.47 0.33 5.99 1.527 339.8 9.93 0.05
1.55 8.71 4.50 1.488 337.1 9.75 0.05
359
TABLE
2
Spectroscopic
parameters
for Er3+ and Tm3+ ions in three binary
glasses
Parameter
SFSP
Er3’ SBSP
SASP
SFSP
Tm3+ SBSP
SASP
E 1 (cm-‘) E2 (cm-‘) E3 (cm-‘) t4f (cm -1 (Y (cm-‘)
6678.9
6625.8 26.8 654.5 2375.0 15.2
6794.4 33.7 659.2 2396.7 20.1
7096.6 34.6 713.3 2653.6 -
6660.8 32.4 700.5 2659.2 -
7077.8 35.4 702.6 2663.6
30.6 649.2 1
2395.8 13.7
a,( XIOzo cm2) !J4( X 10zo cm2) fi2,( X1020 cm2) ;f2
3.01 4.79 0.38 433.3 1.488
8.88 1.06 3.18 420.5 1.487
7.40 3.04 3.05 449.3 1.501
10.29
10.12
10.31
9.95
9.51
10.07
0.05
0.05
0.05
0.05
0.05
0.05
El/E3 E2/E3
8.50 0.17 2.65 473.5 1.494
9.84 1.85 3.36 452.4 1.493
7.32 3.85 1.71 472.9 1.492
The Slater-Condon parameter (F,) of a rare earth ion is related atomic number [ 141, according to the equation: F2 = 12.4(2 - 34) This parameter as follows: F2 =
to its (1)
can also be expressed
through
the Racah (Ek) parameter
E’ + 143E2 + llE3 42
(2)
It is noteworthy that the F2 values obtained through eqn. (1) (Pr3+ = 310 Nd3+ = 322 Er3+ = 422 and Tm 3+ = 434) and eqn. (2) (Tables 1 and 2) are in good agree’ment. 3.2. Radiative lifetimes The computed values of the radiative lifetimes (ra) for certain excited states of Pr3+, Nd3+, Er3+ and Tm3+ ions in all three binary glasses are given in Table 3. It is interesting to note that 3F3 and 3P, lasing levels of the Pr3+ ion yield maximum and minimum lifetimes (ra) respectively and 3P, and 3P, levels exhibit equal magnitudes in their lifetimes. SBSP and SASP glasses yield equal lifetimes for the fluorescent levels of Nd3+ (4Gs,2 and 4G7,2) and Er3+ (2H9,2 and 4G,,,2) ions. In the case of the Tm3+ ion, the ‘D2 level could only be observed in SBSP glass and therefore its lifetime was estimated. 3.3. Branching ratios The lasing potency indicative branching ratio [6,15] parameter for Pr3+, Nd3+, Er3+ and Tm3+ ions in the three glass environments yielded highest values for their lasing lines as shown below:
360 TABLE 3 Radiative lifetimes (in ps) of fluorescent levels of Pr3+, Nd3+, Er3+ and Tm3+ ions in three binary glasses Zon
Level
SFSP
SBSP
SASP
1567 214 32 32
1499 302 38 36
1167 179 24 25
457 331 333 76 92 18
474 356 353 70 85 149
288 236 314 70 85 138
11531 15873 2702 486 2353 287 506 487 47
4348 3215 5435 572 279 627 237 190 28
4082 3279 2994 421 316 155 192 191 27
329
305 25
3F3
Pr3+
lD* 3h 3b
4F 312 4F5 12
4F 912
Nd3+
4G5
12
4G7/2 ‘G9/2
41 1312 41 41:::2 4F 912 4S 312 4F II2 4F s/2
Er3+
‘H9,2
4G 11/2 Tm3+
‘G4 932
Pr3+: 3P, -
-
340
3H,
Nd3+: 4F3,2 Er3+: 4113/2
-
-
Tm3+: 3H4 -
4111,2 4115/2
3H,
3.4. Splitting of energy levels The second derivative spectra at times give much more information than the normal spectra. In the present case, certain bands in the second derivative spectra are found to have split into two components. The splittings thus observed could not be attributed to any electronic levels as there are no such electronic levels in the neighbourhood. They could not be attributed to any chemical impurity as high-grade chemicals were used. As the glasses under study are phosphate glasses, these splittings of the bands are quite possibly a result of superposition of the vibrational modes of P043- radical on the electronic levels of rare earth ions. Further, the
361
splitting observed for the bands are in close agreement with the fundamental vibrational frequencies of the POa3- radical [ 161 as shown below: 4I9,2 of Er3+ in SFSP:
80 cm-’ (v3 - vi)
4F 9,2 of Er3+ in SFSP:
188 cm-’ 2(v3 - vi)
3F3 of Tm3+ in SBSP:
298 cm-’ (vi + u2 - v3)
‘G4 of Tm3+ in SASP:
557 cm-l (v3 - V4)
where v1 = 980 cm-‘, v2 = 363 cm-‘, v3 = 1082 cm-’ and v4 = 515 cm-‘. This therefore supports our view that there is an overlapping of the vibrational levels of the P043- radical with the electronic levels of Er3+ and Tm3+ ions in the respective glasses.
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
M. J. Weber, Am. Chem. Sot. Symp. Ser., 131 Washington, DC 1980. T. Izumittani, H. Toratani and H. Kuroda, J. Non-Cryst. Solids, 47 (1982) 87. M. J. Weber, J. Non-Cryst. Solids, 4.2 (1980) 189. M. J. Weber, D. C. Ziegler and C. A. Angell, J. Appl. Phys., 53 (1982) 4344. M. J. Weber, J. Non-Cryst. Solids, 47 (1982) 117. R. Reisfeld and C. K. Jorgensen, Laser and Excited States of Rare Earths, SpringerVerlag, Berlin, 1977. M. J. Weber and R. M. Almeida, J. Non-Cryst. Solids, 43 (1981) 99. S. E. Stokowski, W. E. Martin and S. M. Yarema, J. Non-Cryst. Solids, 40 (1980) 481. S. V. J. Lakshman and A. Suresh Kumar, J. Phys. Chem. Solids, 49 (1988) 133. S. V. J. Lakshman and A. Suresh Kumar, J. Non-Cryst. Solids, 85 (1986) 162. P. F. Kerr, Optical Mineralogy, McGraw-Hill, New York, 1969. C. D. Coleman, W. R. Bozman and W. F. Meggers, Tables of Wavenumbers, NBS Monographs, U.S. Department of Commerce, Washington, DC, 1960. B. G. Wybourne, Spectroscopic Properties of Rare Earths, Interscience, New York, 1965. G. H. Dieke, Spectra and Energy Levels of Rare Earths Ions in Crystals, Academic Press, New York, 1968. A. A. Kaminskii, Laser Crystals, Springer-Verlag, Berlin, 1981. G. Herzberg, Molecular Spectra and Molecular Structure ZZ. Infrared and Raman Spectra of Polyatomic Molecules, Van Nostrand, New York, 1954.
Metals, 148 (1989)
357
357 - 361
SPECTROSCOPIC STUDIES ON Pr(III), Nd(III), Er(II1) AND Tm(II1) IONS IN FLUORO-, BORO- AND ACETOPHOSPHATE GLASS ENVIRONMENTS* A. SURESH
KUMAR
Department
of USIC, S. V. University, Tirupati - 517 502 (India)
S. V. J. LAKSHMAN Department (Received
of Physics, S. V. University, Tirupati - 517 502 (India)
June
8, 1988;
in revised form September
14, 1988)
Summary Spectral results of Pr(III), Nd(III), Er(III), Tm(II1) ions in fluoro (SFSP), boro (SBSP) and aceto (SASP) phosphate glass environments are reported. Spectroscopic parameters such as Racah, spin-orbit, configuration interaction and Judd-Ofelt intensity parameters have been evaluated. Lifetimes and branching ratios for certain lasing levels have been estimated. The splittings observed for certain bands in the second derivative spectra can be satisfactorily explained by superposition of the vibrational modes of the phosphate radical on the electronic bands.
1. Introduction Spectroscopic properties of ions depend strongly upon the environment of the laser ions with which they are surrounded [ 1,2]. Several tailoring techniques have been employed to alter the spectroscopic properties of rare earth ions in several media [ 3 - 51 to yield favourable situations for lasing action. The glass environments for rare earth ion laser action have certain advantages over their counterparts such as crystals, liquids and gases [ 61. Phosphate glass environments have indicated good laser action for certain rare earth ions [2, 3,7 - 91. In the present study, we have imposed fluoro-, boro- and acetophosphate glass environments on Pr3+, Nd3+, Er3+ and Tm3+ ions and evaluated the lifetimes and branching ratios for certain laser transitions.
*Paper presented at the September 12 - 16, 1988.
18th
Rare
Earth
Research
@ Elsevier
Conference,
Sequoia/Printed
Lake
Geneva,
WI,
in The Netherlands
358
2. Experimental details Good glass samples were prepared using the quenching method [lo]. One mol.% of rare earth (Pr, Nd, Er and Tm) ions was added in each of the glass composition shown below: sodium fluoride: sodium hexametaphosphate (SFSP), 70:29 sodium tetraborate: sodium hexametaphosphate (SBSP), 20: 39 sodium acetate : sodium hexametaphosphate (SASP), 30 : 69 Good glasses were formed at temperatures of 650, 750 and 750 “C respectively. Absorption spectra were recorded in the UV-VIS and near-IR regions on Perkin-Elmer 551 or Carl Zeiss Specord 61 spectrophotometers. The refractive indices of these glasses were measured using the “Becke line” method [ll]. The wavelengths of the bands were converted into vacuum wavenumbers using NBS wavenumber tables [ 121.
3. Results and discussion 3.1. Racah parameters The Racah (Ek), spin-orbit (&), configurational interaction ((Y, /3)and Judd-Ofelt intensity (a,, &, &) parameters derived from the spectral data are presented in Tables 1 and 2. From these tables it is noted that the ratios of E l/E3 and E 2/E3 are found to be nearly equal to 10 and 0.05 respectively for the four ions studied. This indicates that the radial properties are hydrogenie [ 131 and are unaffected by the environment.
TABLE
1
Spectroscopic
parameters
for Pr3+ and Nd3+ ions in three binary
glasses
Parameter
SFSP
Pr3+ SBSP
SASP
SFSP
Nd3+ SBSP
SASP
E’ (cm-‘)
4725.2 22.7 467.4 739.2 5.3 -457.02 8.80 1.31 7.06 1.492 312.2 10.11 0.05
4104.0 20.5 424.2 734.3 -53.3 802.6 6.32 1.31 8.21 1.492 278.6 9.67 0.05
4688.1 22.0 456.7 722.2 -2.8 -408.2 11,96 2.06 8.50 1.478 306.2 10.27 0.05
4909.5 26.1 503.0 860.8 5.0 -
5009.6
4883.5 26.3 500.9 876.7 4.6 -
EZ (cm-‘) E3 (cm-‘) t4f a
(cm+)
(cm-‘)
P (cm-‘) R,( XIOzo cm2) !i24( XIOzo cm2) Qj( XIOzo cm2) l2
El/E3 E2/E3
6.19 0.59 6.93 1.490 337.6 9.76 0.04
26.0 504.6 833.3 3.9 6.47 0.33 5.99 1.527 339.8 9.93 0.05
1.55 8.71 4.50 1.488 337.1 9.75 0.05
359
TABLE
2
Spectroscopic
parameters
for Er3+ and Tm3+ ions in three binary
glasses
Parameter
SFSP
Er3’ SBSP
SASP
SFSP
Tm3+ SBSP
SASP
E 1 (cm-‘) E2 (cm-‘) E3 (cm-‘) t4f (cm -1 (Y (cm-‘)
6678.9
6625.8 26.8 654.5 2375.0 15.2
6794.4 33.7 659.2 2396.7 20.1
7096.6 34.6 713.3 2653.6 -
6660.8 32.4 700.5 2659.2 -
7077.8 35.4 702.6 2663.6
30.6 649.2 1
2395.8 13.7
a,( XIOzo cm2) !J4( X 10zo cm2) fi2,( X1020 cm2) ;f2
3.01 4.79 0.38 433.3 1.488
8.88 1.06 3.18 420.5 1.487
7.40 3.04 3.05 449.3 1.501
10.29
10.12
10.31
9.95
9.51
10.07
0.05
0.05
0.05
0.05
0.05
0.05
El/E3 E2/E3
8.50 0.17 2.65 473.5 1.494
9.84 1.85 3.36 452.4 1.493
7.32 3.85 1.71 472.9 1.492
The Slater-Condon parameter (F,) of a rare earth ion is related atomic number [ 141, according to the equation: F2 = 12.4(2 - 34) This parameter as follows: F2 =
to its (1)
can also be expressed
through
the Racah (Ek) parameter
E’ + 143E2 + llE3 42
(2)
It is noteworthy that the F2 values obtained through eqn. (1) (Pr3+ = 310 Nd3+ = 322 Er3+ = 422 and Tm 3+ = 434) and eqn. (2) (Tables 1 and 2) are in good agree’ment. 3.2. Radiative lifetimes The computed values of the radiative lifetimes (ra) for certain excited states of Pr3+, Nd3+, Er3+ and Tm3+ ions in all three binary glasses are given in Table 3. It is interesting to note that 3F3 and 3P, lasing levels of the Pr3+ ion yield maximum and minimum lifetimes (ra) respectively and 3P, and 3P, levels exhibit equal magnitudes in their lifetimes. SBSP and SASP glasses yield equal lifetimes for the fluorescent levels of Nd3+ (4Gs,2 and 4G7,2) and Er3+ (2H9,2 and 4G,,,2) ions. In the case of the Tm3+ ion, the ‘D2 level could only be observed in SBSP glass and therefore its lifetime was estimated. 3.3. Branching ratios The lasing potency indicative branching ratio [6,15] parameter for Pr3+, Nd3+, Er3+ and Tm3+ ions in the three glass environments yielded highest values for their lasing lines as shown below:
360 TABLE 3 Radiative lifetimes (in ps) of fluorescent levels of Pr3+, Nd3+, Er3+ and Tm3+ ions in three binary glasses Zon
Level
SFSP
SBSP
SASP
1567 214 32 32
1499 302 38 36
1167 179 24 25
457 331 333 76 92 18
474 356 353 70 85 149
288 236 314 70 85 138
11531 15873 2702 486 2353 287 506 487 47
4348 3215 5435 572 279 627 237 190 28
4082 3279 2994 421 316 155 192 191 27
329
305 25
3F3
Pr3+
lD* 3h 3b
4F 312 4F5 12
4F 912
Nd3+
4G5
12
4G7/2 ‘G9/2
41 1312 41 41:::2 4F 912 4S 312 4F II2 4F s/2
Er3+
‘H9,2
4G 11/2 Tm3+
‘G4 932
Pr3+: 3P, -
-
340
3H,
Nd3+: 4F3,2 Er3+: 4113/2
-
-
Tm3+: 3H4 -
4111,2 4115/2
3H,
3.4. Splitting of energy levels The second derivative spectra at times give much more information than the normal spectra. In the present case, certain bands in the second derivative spectra are found to have split into two components. The splittings thus observed could not be attributed to any electronic levels as there are no such electronic levels in the neighbourhood. They could not be attributed to any chemical impurity as high-grade chemicals were used. As the glasses under study are phosphate glasses, these splittings of the bands are quite possibly a result of superposition of the vibrational modes of P043- radical on the electronic levels of rare earth ions. Further, the
361
splitting observed for the bands are in close agreement with the fundamental vibrational frequencies of the POa3- radical [ 161 as shown below: 4I9,2 of Er3+ in SFSP:
80 cm-’ (v3 - vi)
4F 9,2 of Er3+ in SFSP:
188 cm-’ 2(v3 - vi)
3F3 of Tm3+ in SBSP:
298 cm-’ (vi + u2 - v3)
‘G4 of Tm3+ in SASP:
557 cm-l (v3 - V4)
where v1 = 980 cm-‘, v2 = 363 cm-‘, v3 = 1082 cm-’ and v4 = 515 cm-‘. This therefore supports our view that there is an overlapping of the vibrational levels of the P043- radical with the electronic levels of Er3+ and Tm3+ ions in the respective glasses.
References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
M. J. Weber, Am. Chem. Sot. Symp. Ser., 131 Washington, DC 1980. T. Izumittani, H. Toratani and H. Kuroda, J. Non-Cryst. Solids, 47 (1982) 87. M. J. Weber, J. Non-Cryst. Solids, 4.2 (1980) 189. M. J. Weber, D. C. Ziegler and C. A. Angell, J. Appl. Phys., 53 (1982) 4344. M. J. Weber, J. Non-Cryst. Solids, 47 (1982) 117. R. Reisfeld and C. K. Jorgensen, Laser and Excited States of Rare Earths, SpringerVerlag, Berlin, 1977. M. J. Weber and R. M. Almeida, J. Non-Cryst. Solids, 43 (1981) 99. S. E. Stokowski, W. E. Martin and S. M. Yarema, J. Non-Cryst. Solids, 40 (1980) 481. S. V. J. Lakshman and A. Suresh Kumar, J. Phys. Chem. Solids, 49 (1988) 133. S. V. J. Lakshman and A. Suresh Kumar, J. Non-Cryst. Solids, 85 (1986) 162. P. F. Kerr, Optical Mineralogy, McGraw-Hill, New York, 1969. C. D. Coleman, W. R. Bozman and W. F. Meggers, Tables of Wavenumbers, NBS Monographs, U.S. Department of Commerce, Washington, DC, 1960. B. G. Wybourne, Spectroscopic Properties of Rare Earths, Interscience, New York, 1965. G. H. Dieke, Spectra and Energy Levels of Rare Earths Ions in Crystals, Academic Press, New York, 1968. A. A. Kaminskii, Laser Crystals, Springer-Verlag, Berlin, 1981. G. Herzberg, Molecular Spectra and Molecular Structure ZZ. Infrared and Raman Spectra of Polyatomic Molecules, Van Nostrand, New York, 1954.