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On the luminescence of the Bz3+ ion in gadolinium oxide
Journal of Luminescence 23(1981) 237—240 North-Holland Publishing Company
237
ON THE LUMINESCENCE OF THE Bz3~ ION IN GADOLINIUM OXIDE O BOEN HO and G. BLASSE Physical Laboratory, State Unicersity, P.O. Box 80000, 3508 TA Uirecht, The Netherlands Original manuscript received 14 October 1980 Revised manuscript received II March 1981
The luminescence properties of Gd 203 : Bi with the B rare-earth oxide structure are 3 + ions. oxide reported. The luminescence decay times of Gd203 : Bi with B and C rare-earth structure are very short at LHeT. This is ascribed to the presence of the Gd
I. Introduction It is well known that Gd 203 occurs in two modifications, viz, the monoclinic B and the cubic C rare-earth oxide structure [1]. The luminescence of the 3~ion in Gd Bi 203 with the C rare-earth oxide structure has been reported by Boulon [2]. He observed bands, a blue 3 + on two the emission two crystallographic sitesand (S a green one, which were ascribed to Bi 6 and C2 symmetry, respectively). At low temperatures long decay times3Pwere observed (100—800 p~s),which were ascribed to the occupation of the 0 level. Transitions from this level to the ground state ‘S0 are 3strongly forbidden. + -activated compounds [3] we prepared the course of of our studies onThis Bi structure contains three crystallographic the In B-modification Gd 2°3 : Bi. sites for Gd3 ~ Two of these are six, the third is seven coordinated. We observed a blue-green luminescence. Our decay time measurements revealed an abnormal behaviour for the Bi3~decay times in gadolinium host lattices.
2. Experimental Samples were prepared from Gd 203 (99.999%, Highways International) and Bi203 (J.T. Baker). The bismuth concentration was I mol%. Firing at 1200°C yielded samples with the B structure while firing at 1000°C for 2 h yielded samples which contained mainly the C modification. Additional doping with 0022-2313/81 /0000—0000/$02.50 © 1981 North Holland
0 Boen Ho and G. Blasse / Luminescence of Gd,0
238
3: BE
1 mol% Lu203 (99.99%, Fluka A.G.) suppressed the amount of the B-modified substance in the low-temperature fired samples to a negligible concentration. Samples were checked by X-ray powder analysis using CuKa radiation. Optical measurements were performed as described before [4].
3. Results At low temperatures all Gd 203 : Bi samples give an efficient luminescence. The thermal quenching temperatures are at about room temperature. The luminescence spectra of Gd 203: Bi with C structure agree with those reported by Boulon [2] and Datta [5]. The spectrum of Gd2O3: Bi with the B structure is shown in fig. 1. There is one, blue-green emission band (maximum at 475 nm) and an excitation band (maximum at 375 nm) in the near ultraviolet. Table I gives the decay times, measured at LHeT. The decay curves were all single exponentials within the apparatus accuracy. Note the large difference between our values (about 1 its) and what is found usually (about 1 ms, ref. [2]).
4. Discussion 3~ion is due to transitions from the excited 3P, and 3P The emission of the Bi 0 levels (originating from the sp configuration) 3P to the ‘S0 ground state (~2 configuration). At low temperatures the ‘S0 0 transition dominates. Due to the forbidden nature of this transition the decay time of the low-temperature ~—
300
380
460
540
X(nm)—
Fig. 1. Emission and excitation spectrum of the B modification of Gd 203 Bi at LHeT. tl~~ gives the spectral radiant power per unit wavelength in arbitrary units; q~gives the relative quantum yield.
0 Boen Ho and G. Blasse / Luminescence of Gd,0
3: Bi
239
Table I 3~decay time at LHeT of the B and C modification of Gd The values of the Bi 203 : Bi. The system decay time is about 30 ns. Structure
Excitation (nm)
Emission (nm)
B
375
475
830
this work
C(C,)
340
530
1190
thiswork
C(S 6)
370
410
Decay time
Ref.
r(ns)
I60Xl0~~ 3J 800>< i0
[2]
190
this work
IOOX l0~ 500>< iO~)
[2]
1S emission is long (about 1 ms) [2]. At higher temperatures the 0 f— emission takes over and the decay time becomes considerably shorter (about 1 p~s). Broad emission and excitation bands are due to transitions between the ~ and ~ levels. It is remarkable that B-Gd 203 : Bi shows only one emission band, because the crystal structure offers three crystallographic sites for the cations. All three have very low symmetry, viz. C~. According to Wyckoff [6] each site has six anion neighbours and3~ one two203 others at somewhat in or C-Gd (which has two longer quite distances.sites) No has sitebeen preference of [2,5], Bi so that it does not seem very probable different observed that the Bi3 + ion has site preference in B-Gd 203. Thus the spectral characteristics of Bi3~on the three sites of the B structure must be very much alike. In fact, the crystallographic differences between these three sites is less pronounced than that between the two in the C structure. The peculiar behaviour of the B- and C-Gd 203: Bi samples lies in the low-temperature decay time value. We have no explanation for the difference between the values reported for C-Gd 203: Bi by Boulon [2] and ourselves. Note that. the Bi3~concentration was the same in both investigations. Also for NaGdO 2: Bi and LiGdO2 : Bi low-temperature decay time values of the order of 1 ~s have been reported [3,7]. In similar host lattices containing La, Y or Lu instead of Gd the bismuth ion shows the expected low-temperature behaviour with a long decay time. In all compounds LiLnO2 and NaLnO2 the lanthamde (Ln) ions occupy octahedral sites with site symmetries depending on the crystal structure (D3d, D2d and C~,see ref. [7]).The comparison between NaGdO2: Bi and NaLaO2 : Bi is especially interesting, becauseviz. these 3+ the same coordination, D compounds are isomorphous, giving Bi 2d ccordination. Nevertheless their decay times at LHeT differ by is two orders of 3 + ion occupies a site which comparable magnitude [7]. In LiGdO2: Bi the Bi ~
240
0 Boen Ho and G. Blasse
/
Luminescence of Gd,0
3: Bi
with those in B-Gd 203, viz. C~six-coordination. 3~ seemsvary highiy improbable that the sequencebyof the energy levelsofoflanthanide the Bi ionItwould in chemically related compounds variation ions. Therefore we suggest that Gd3~ itself is responsible for the observed short decay times. An obvious possibility is the presence of a high magnetic moment on this ion (4f7 configuration). A molecular magnetic field at the site of a Bi3~ion could mix the 3P 3P 1S 3P 0 and 1 levels strongly. The 0 ~— 0 transition probability will increase considerably then. Effects due to the presence of an external magnetic field have been reported in the literature 1S [8]. 3P Also Ellervee et al. [9,10] have recently shown convincingly that the 0— 0 transition probability is increased by the presence of a nuclear magnetic field.
References [1] [2] [3] [4] [5] [6] [7] [8] [9) [10]
O.J.
Guentert and R.L. Mozzi, Acta Cryst. 11(1958) 746. G. Boulon, J. Physique 32 (1971) 333. See e.g. A.C. Van der Steen, Thesis, Utrecht 1980 (available upon request). H. Ronde and G. Blasse, J. Inorg. NucI. Chem. 40 (1978) 215. R.K. Datta, J. Electrochem. Soc. 114 (1967) 1057. R.W.G. Wyckoff, Crystal Structures, Vol.2 (Interscience, New York, 1964) p. II. A.C. Van der Steen, A.P. Slok and J.J.A. Van Hesteren, J. Electrochem. Soc. 128 (1981) 1327. W.A. Runciman, N.B. Manson and M. Marshall, J. Lumin. 12/13 (1976) 413. G.S. Zavt and A.F. Ellervee, Phys. Stat. Sol. (b) 93 (1979) 757. A.F. Ellervee, A.!. Lausaar and A.M.A. Oner, Pisma JETP 33 (1981) 24.
237
ON THE LUMINESCENCE OF THE Bz3~ ION IN GADOLINIUM OXIDE O BOEN HO and G. BLASSE Physical Laboratory, State Unicersity, P.O. Box 80000, 3508 TA Uirecht, The Netherlands Original manuscript received 14 October 1980 Revised manuscript received II March 1981
The luminescence properties of Gd 203 : Bi with the B rare-earth oxide structure are 3 + ions. oxide reported. The luminescence decay times of Gd203 : Bi with B and C rare-earth structure are very short at LHeT. This is ascribed to the presence of the Gd
I. Introduction It is well known that Gd 203 occurs in two modifications, viz, the monoclinic B and the cubic C rare-earth oxide structure [1]. The luminescence of the 3~ion in Gd Bi 203 with the C rare-earth oxide structure has been reported by Boulon [2]. He observed bands, a blue 3 + on two the emission two crystallographic sitesand (S a green one, which were ascribed to Bi 6 and C2 symmetry, respectively). At low temperatures long decay times3Pwere observed (100—800 p~s),which were ascribed to the occupation of the 0 level. Transitions from this level to the ground state ‘S0 are 3strongly forbidden. + -activated compounds [3] we prepared the course of of our studies onThis Bi structure contains three crystallographic the In B-modification Gd 2°3 : Bi. sites for Gd3 ~ Two of these are six, the third is seven coordinated. We observed a blue-green luminescence. Our decay time measurements revealed an abnormal behaviour for the Bi3~decay times in gadolinium host lattices.
2. Experimental Samples were prepared from Gd 203 (99.999%, Highways International) and Bi203 (J.T. Baker). The bismuth concentration was I mol%. Firing at 1200°C yielded samples with the B structure while firing at 1000°C for 2 h yielded samples which contained mainly the C modification. Additional doping with 0022-2313/81 /0000—0000/$02.50 © 1981 North Holland
0 Boen Ho and G. Blasse / Luminescence of Gd,0
238
3: BE
1 mol% Lu203 (99.99%, Fluka A.G.) suppressed the amount of the B-modified substance in the low-temperature fired samples to a negligible concentration. Samples were checked by X-ray powder analysis using CuKa radiation. Optical measurements were performed as described before [4].
3. Results At low temperatures all Gd 203 : Bi samples give an efficient luminescence. The thermal quenching temperatures are at about room temperature. The luminescence spectra of Gd 203: Bi with C structure agree with those reported by Boulon [2] and Datta [5]. The spectrum of Gd2O3: Bi with the B structure is shown in fig. 1. There is one, blue-green emission band (maximum at 475 nm) and an excitation band (maximum at 375 nm) in the near ultraviolet. Table I gives the decay times, measured at LHeT. The decay curves were all single exponentials within the apparatus accuracy. Note the large difference between our values (about 1 its) and what is found usually (about 1 ms, ref. [2]).
4. Discussion 3~ion is due to transitions from the excited 3P, and 3P The emission of the Bi 0 levels (originating from the sp configuration) 3P to the ‘S0 ground state (~2 configuration). At low temperatures the ‘S0 0 transition dominates. Due to the forbidden nature of this transition the decay time of the low-temperature ~—
300
380
460
540
X(nm)—
Fig. 1. Emission and excitation spectrum of the B modification of Gd 203 Bi at LHeT. tl~~ gives the spectral radiant power per unit wavelength in arbitrary units; q~gives the relative quantum yield.
0 Boen Ho and G. Blasse / Luminescence of Gd,0
3: Bi
239
Table I 3~decay time at LHeT of the B and C modification of Gd The values of the Bi 203 : Bi. The system decay time is about 30 ns. Structure
Excitation (nm)
Emission (nm)
B
375
475
830
this work
C(C,)
340
530
1190
thiswork
C(S 6)
370
410
Decay time
Ref.
r(ns)
I60Xl0~~ 3J 800>< i0
[2]
190
this work
IOOX l0~ 500>< iO~)
[2]
1S emission is long (about 1 ms) [2]. At higher temperatures the 0 f— emission takes over and the decay time becomes considerably shorter (about 1 p~s). Broad emission and excitation bands are due to transitions between the ~ and ~ levels. It is remarkable that B-Gd 203 : Bi shows only one emission band, because the crystal structure offers three crystallographic sites for the cations. All three have very low symmetry, viz. C~. According to Wyckoff [6] each site has six anion neighbours and3~ one two203 others at somewhat in or C-Gd (which has two longer quite distances.sites) No has sitebeen preference of [2,5], Bi so that it does not seem very probable different observed that the Bi3 + ion has site preference in B-Gd 203. Thus the spectral characteristics of Bi3~on the three sites of the B structure must be very much alike. In fact, the crystallographic differences between these three sites is less pronounced than that between the two in the C structure. The peculiar behaviour of the B- and C-Gd 203: Bi samples lies in the low-temperature decay time value. We have no explanation for the difference between the values reported for C-Gd 203: Bi by Boulon [2] and ourselves. Note that. the Bi3~concentration was the same in both investigations. Also for NaGdO 2: Bi and LiGdO2 : Bi low-temperature decay time values of the order of 1 ~s have been reported [3,7]. In similar host lattices containing La, Y or Lu instead of Gd the bismuth ion shows the expected low-temperature behaviour with a long decay time. In all compounds LiLnO2 and NaLnO2 the lanthamde (Ln) ions occupy octahedral sites with site symmetries depending on the crystal structure (D3d, D2d and C~,see ref. [7]).The comparison between NaGdO2: Bi and NaLaO2 : Bi is especially interesting, becauseviz. these 3+ the same coordination, D compounds are isomorphous, giving Bi 2d ccordination. Nevertheless their decay times at LHeT differ by is two orders of 3 + ion occupies a site which comparable magnitude [7]. In LiGdO2: Bi the Bi ~
240
0 Boen Ho and G. Blasse
/
Luminescence of Gd,0
3: Bi
with those in B-Gd 203, viz. C~six-coordination. 3~ seemsvary highiy improbable that the sequencebyof the energy levelsofoflanthanide the Bi ionItwould in chemically related compounds variation ions. Therefore we suggest that Gd3~ itself is responsible for the observed short decay times. An obvious possibility is the presence of a high magnetic moment on this ion (4f7 configuration). A molecular magnetic field at the site of a Bi3~ion could mix the 3P 3P 1S 3P 0 and 1 levels strongly. The 0 ~— 0 transition probability will increase considerably then. Effects due to the presence of an external magnetic field have been reported in the literature 1S [8]. 3P Also Ellervee et al. [9,10] have recently shown convincingly that the 0— 0 transition probability is increased by the presence of a nuclear magnetic field.
References [1] [2] [3] [4] [5] [6] [7] [8] [9) [10]
O.J.
Guentert and R.L. Mozzi, Acta Cryst. 11(1958) 746. G. Boulon, J. Physique 32 (1971) 333. See e.g. A.C. Van der Steen, Thesis, Utrecht 1980 (available upon request). H. Ronde and G. Blasse, J. Inorg. NucI. Chem. 40 (1978) 215. R.K. Datta, J. Electrochem. Soc. 114 (1967) 1057. R.W.G. Wyckoff, Crystal Structures, Vol.2 (Interscience, New York, 1964) p. II. A.C. Van der Steen, A.P. Slok and J.J.A. Van Hesteren, J. Electrochem. Soc. 128 (1981) 1327. W.A. Runciman, N.B. Manson and M. Marshall, J. Lumin. 12/13 (1976) 413. G.S. Zavt and A.F. Ellervee, Phys. Stat. Sol. (b) 93 (1979) 757. A.F. Ellervee, A.!. Lausaar and A.M.A. Oner, Pisma JETP 33 (1981) 24.