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Luminescence and excitation spectra of Ce3+-Tb3+ ions co-doped in the LnMgB5O10 system
Journal of the Less-Common
Metals, 148 (1989)
393 - 397
393
LUMINESCENCE AND EXCITATION SPECTRA OF Ce3+-Tb3+ IONS CO-DOPED IN THE LnMgBsO,, SYSTEM* DING XIYI Beijing General Research Institute for Non-Ferrous wai Dajie, Beijing (China)
Metals, China, 2 xin jie Kou
(Received May 31, 1988; in revised form September 15, 1988)
Summary The luminescence and excitation spectra of Ce3+--Tb3+ co-doped compounds Ln, _ _,Ce,Tb,MgBsO,,, (Ln = La, Gd or Y) have been studied. The maximum intensity and integrated intensity for each peak in the excitation spectra with varying 3c or y were measured. For various rare earth matrices, the relative brightness shows that Tb3+ emission is the most efficient in Gd3+containing compounds with 254 nm UV excitation. Tb3+ emission is efficient in YMgBsOie:Ce,Tb with 365 nm UV excitation. However, Tb3+ emission in LaMgB,Oi,,:Ce,Tb is not efficient with 365 nm UV excitation because its excitation peak falls off in intensity at 360 nm.
1. Introduction In recent years, investigations of luminescence of rare earth borates co-doped with Ce-Tb have been reported [l - 41. Blasse and coworkers [ 5, 61 investigated luminescence and energy migration in TbMgB50i0 and EuMgBsO,, in detail. In this paper we discuss the luminescence and excitation spectra dependence on composition in the Ln, _,_,Ce,Tb,MgBsOi,, (Ln = La, Gd or Y) system.
2. Experimental details The starting materials used for the syntheses were LazOs, YzOs, GdzOs, CeO, and Tb40, (99.95% pure). The rare earth oxides, in stoichiometric quantities, were dissolved in nitric acid and precipitated by oxalic acid. The precipitate was fired to form the oxide and was fully mixed with the opti*Paper presented at the 18th Rare Earth Research Conference, September 12 - 16,1988. 0022-5088/89/$3.50
0 Elsevier Sequoia/Printed
Lake Geneva, WI.
in The Netherlands
394
mum quantities of MgO and HsBOs. The mixture was fired for 2 - 6 h at 1000 “C, finely ground and again fired at the same temperature and for the same time in H,--N, mixed gas, and the product was washed and dried. The X-ray analysis shows that the powder samples contain mostly the LnMgBsO,, phase with some LnB03 phase. All UV-excited emission and excitation spectra were recorded using a Fuorolog model 212 spectrophotometer. The excitation spectra are recorded by monitoring Tb3+ emission at 542 nm.
3. Results and discussion Tb3+ emission spectra of all LnMgB,Ora:Tb (Ln = La, Gd or Y) samples containing cerium or without cerium, even at low terbium concentration, show typical strong sharp lines in the green region (Fig. 1). Tb3+ emission occurred for 5D4-7F3 transitions and no ‘D3 state could be observed. The maximum intensity line is at 542 nm. GdMgB,Ora:Ce,Tb is well known as a green phosphor used in high-efficiency lamps. The excitation spectrum of Tb3’ emission in the Lnr _ x _ ,Ce,Tb,MgBsOr0 system changes with 3t and y. We measured the maximum intensity, Max I, and the integrated intensity, ZI, of each excitation peak and calculated the Tb:Ce intensity ratio. The data of four typical ratios are given in Table 1. An example of an excitation spectrum is shown in Fig. 2. For practical purposes we have measured the relative brightness of samples using low- or high-pressure mercury vapor discharge lamps as the UV-excitation sources. The results are given in Fig. 3. From the data contained in the above figures and table the following conclusions can be drawn. con(1) The excitation spectrum of Tb3+ emission in LnMgBsO,,:Tb sists of a broad band and a series of lines (Fig. 4). The band spectrum shows Tb3+ excitation and has a main peak at 244 nm. This peak for lanthanum 6.55X106
-
ex = 280 nm
A 380
500 Wavelength
780 (nm)
Fig. 1. Emission spectrum of GdMgB5010:Ce,Tb.
395
TABLE 1 The ratio of maximum intensity and integrated intensity of excitation peaks for Ce”+ and Tb3+ in LnMgBsO1e:Ce,Tb RE matrices
La Gd Y
Tb:Ce intensity ratio
1:0.75
Tb3+ peak (nm)
Ce3+ peak (nm)
Max ITb:Max I,,
XI,:
XI,,
284 282 282
330 360 366
0.71 5.44 2.01
0.7 4.23 1.51
La Gd Y
1:l
284 282 282
330 358 366
0.60 2.76 2.87
0.615 1.99 1.57
La Gd Y
1:2
282 280 282
330 360 366
1.50 2.36 1.15
1.40 1.73 0.82
La Gd Y
1:5
284 280 282
330 360 366
1.01 2.93 1.24
0.94 2.10 0.86
I
looI
>
>.
c
c
E
$ C
e
e aa
300.0
200.0
400.0
50.
O0
0.5
Wavelength(nm) Fig. 2. Excitation 0.020Tb
1.0
1.5
2.0
2.5
TbSeMoXO.l
spectrum of Tb3+ emission (em = 542 nm) in LnMgBs0i0:0.015Ce,
Fig. 3. Intensity of Tb3+ emission in Lno.ss_yCeo.lsTb,MgBsO~~ -, 254 nm; - - -, 365 nm.
under UV excitation:
and yttrium compounds is weaker than that of the gadolinium compound. The series of lines in our spectrum is similar to the spectrum mentioned in ref. 6. In the case of co-doped cerium and terbium, the excitation spectra of Tb3+ emission in LnMgB,O,,: Ce,Tb consist of a broad band with double peaks. One is the Tb3+ excited peak near 282 nm corresponding to the peak at 244 nm in LnMgB,OlO:Tb. The other peak is the excited Ce3+ peak; this shifts slightly for various matrices. For example, it occurs at 330 nm for
396
lanthanum, at 360 nm for gadolinium and at 366 nm for yttrium respectively. (2) Comparison of the three rare earth matrices for *_ GdMgBSOn-,:Ce,Tb shows that Max In, and XIri, are larger than Max Ice ano Z;lce respectively. Their intensity ratios are several times those of lanthanum and yttrium compounds. Gd3+ may transfer excitation energy from Ce3+ to Tb3+ and intensify the Tb3+ 5D,-7F0 emission. Therefore GdMgB5010:Ce,Tb has the most efficient luminescence with UV-excitation at 254 nm (see Fig. 3), making it an excellent lamp phosphor. The excitation spectra of YMgBSOn,:Ce,Tb are very similar to those of GdMgO,Ois:Ce,Tb. All Mtin,:Maxlc, ratios are larger than 1, but if Ce3+ content is five times greater than Tb3+ content, the ratio of integrated intensity ZZ:In,:Zlce is less than 1, so Tb3+ emission at 542 nm can be obtained; this has maximum brightness with 365 nm UV-excitation (see Fig. 3). In the excitation spectra of LaMgBsOiO:Ce,Tb, the two peaks are close to each other and the ratio of maximum intensity and integrated intensity for both peaks are in reverse order. Monitoring Tb3+ 542 nm emission, the Tb3+ excitation peak is smaller than the Ce3+ excitation peak; thus, among the three matrices, the brightness of the lanthanum compounds is the lowest under short UV-excitation. However, Tb3+ emission in LaMgB,Oi,,:Ce, Tb is not efficient with 365 nm UVexcitation because its excitation peak falls off in intensity at 360 nm. (3) The excitation spectra of binary matrix La-Gd and Y-Gd in LnMgBsO,,:Ce,Tb are very similar. The excitation spectrum of the La-Gd system, for example, is given in Fig. 5. In this case, the excitation peak for Ce3+ almost disappears, but the Tb3+ excitation peak at 284 nm is obviously intensified. This clearly shows that Gd plays the role of available intermediary in the energy migration from Ce3+ to Tb3+. Blasse described [4] the procedure of energy migration in Ce-Gd-Tb. We expect that further study will find the
4.68 X 10’
5.38 X 1OS em=542nm
> E
1 z
c
C
e 8
al
‘;
5
C
C 200.00
285.00 Waveiength (nm)
370.00
200.00
300.00 Wavelength (nm)
Fig. 4. Excitation spectrum of GdMgB~Olo:Tb.
Fig. 5. Excitation spectrum of Tb3+ emission (em = 542 nm) in La~.7~Gd~_~&lgB~0~~: Ce,Tb.
397
most suitable composition for high-efficiency luminescence earth mixtures (dependent on the excitation wavelength This will extend the applications of rare earth luminescence.
using binary rare of the material).
References 1 A. W. Veenis and A. Bril, Philips J. Res., 33 (1978) 124. 2 M. Leskela, M. Saakes and G. Blasse, Mater. Res. Bull., 19 (1984) 151. 3 B. Saubat, C. Fouassier, P. Hagenmuller and J. C. Bonrcet, Mater. (1981) 193. 4 G. Blasse, J. Less-Common Met., 112 (1985) 79. 5 M. Buijs and G. Blasse, J. Lumin., 34 (1986) 236. 6 M. Buijs, J. P. M. Van Vliet and G. Blasse, J. Lumin., 35 (1986) 213.
Res. Bull.,
16
Metals, 148 (1989)
393 - 397
393
LUMINESCENCE AND EXCITATION SPECTRA OF Ce3+-Tb3+ IONS CO-DOPED IN THE LnMgBsO,, SYSTEM* DING XIYI Beijing General Research Institute for Non-Ferrous wai Dajie, Beijing (China)
Metals, China, 2 xin jie Kou
(Received May 31, 1988; in revised form September 15, 1988)
Summary The luminescence and excitation spectra of Ce3+--Tb3+ co-doped compounds Ln, _ _,Ce,Tb,MgBsO,,, (Ln = La, Gd or Y) have been studied. The maximum intensity and integrated intensity for each peak in the excitation spectra with varying 3c or y were measured. For various rare earth matrices, the relative brightness shows that Tb3+ emission is the most efficient in Gd3+containing compounds with 254 nm UV excitation. Tb3+ emission is efficient in YMgBsOie:Ce,Tb with 365 nm UV excitation. However, Tb3+ emission in LaMgB,Oi,,:Ce,Tb is not efficient with 365 nm UV excitation because its excitation peak falls off in intensity at 360 nm.
1. Introduction In recent years, investigations of luminescence of rare earth borates co-doped with Ce-Tb have been reported [l - 41. Blasse and coworkers [ 5, 61 investigated luminescence and energy migration in TbMgB50i0 and EuMgBsO,, in detail. In this paper we discuss the luminescence and excitation spectra dependence on composition in the Ln, _,_,Ce,Tb,MgBsOi,, (Ln = La, Gd or Y) system.
2. Experimental details The starting materials used for the syntheses were LazOs, YzOs, GdzOs, CeO, and Tb40, (99.95% pure). The rare earth oxides, in stoichiometric quantities, were dissolved in nitric acid and precipitated by oxalic acid. The precipitate was fired to form the oxide and was fully mixed with the opti*Paper presented at the 18th Rare Earth Research Conference, September 12 - 16,1988. 0022-5088/89/$3.50
0 Elsevier Sequoia/Printed
Lake Geneva, WI.
in The Netherlands
394
mum quantities of MgO and HsBOs. The mixture was fired for 2 - 6 h at 1000 “C, finely ground and again fired at the same temperature and for the same time in H,--N, mixed gas, and the product was washed and dried. The X-ray analysis shows that the powder samples contain mostly the LnMgBsO,, phase with some LnB03 phase. All UV-excited emission and excitation spectra were recorded using a Fuorolog model 212 spectrophotometer. The excitation spectra are recorded by monitoring Tb3+ emission at 542 nm.
3. Results and discussion Tb3+ emission spectra of all LnMgB,Ora:Tb (Ln = La, Gd or Y) samples containing cerium or without cerium, even at low terbium concentration, show typical strong sharp lines in the green region (Fig. 1). Tb3+ emission occurred for 5D4-7F3 transitions and no ‘D3 state could be observed. The maximum intensity line is at 542 nm. GdMgB,Ora:Ce,Tb is well known as a green phosphor used in high-efficiency lamps. The excitation spectrum of Tb3’ emission in the Lnr _ x _ ,Ce,Tb,MgBsOr0 system changes with 3t and y. We measured the maximum intensity, Max I, and the integrated intensity, ZI, of each excitation peak and calculated the Tb:Ce intensity ratio. The data of four typical ratios are given in Table 1. An example of an excitation spectrum is shown in Fig. 2. For practical purposes we have measured the relative brightness of samples using low- or high-pressure mercury vapor discharge lamps as the UV-excitation sources. The results are given in Fig. 3. From the data contained in the above figures and table the following conclusions can be drawn. con(1) The excitation spectrum of Tb3+ emission in LnMgBsO,,:Tb sists of a broad band and a series of lines (Fig. 4). The band spectrum shows Tb3+ excitation and has a main peak at 244 nm. This peak for lanthanum 6.55X106
-
ex = 280 nm
A 380
500 Wavelength
780 (nm)
Fig. 1. Emission spectrum of GdMgB5010:Ce,Tb.
395
TABLE 1 The ratio of maximum intensity and integrated intensity of excitation peaks for Ce”+ and Tb3+ in LnMgBsO1e:Ce,Tb RE matrices
La Gd Y
Tb:Ce intensity ratio
1:0.75
Tb3+ peak (nm)
Ce3+ peak (nm)
Max ITb:Max I,,
XI,:
XI,,
284 282 282
330 360 366
0.71 5.44 2.01
0.7 4.23 1.51
La Gd Y
1:l
284 282 282
330 358 366
0.60 2.76 2.87
0.615 1.99 1.57
La Gd Y
1:2
282 280 282
330 360 366
1.50 2.36 1.15
1.40 1.73 0.82
La Gd Y
1:5
284 280 282
330 360 366
1.01 2.93 1.24
0.94 2.10 0.86
I
looI
>
>.
c
c
E
$ C
e
e aa
300.0
200.0
400.0
50.
O0
0.5
Wavelength(nm) Fig. 2. Excitation 0.020Tb
1.0
1.5
2.0
2.5
TbSeMoXO.l
spectrum of Tb3+ emission (em = 542 nm) in LnMgBs0i0:0.015Ce,
Fig. 3. Intensity of Tb3+ emission in Lno.ss_yCeo.lsTb,MgBsO~~ -, 254 nm; - - -, 365 nm.
under UV excitation:
and yttrium compounds is weaker than that of the gadolinium compound. The series of lines in our spectrum is similar to the spectrum mentioned in ref. 6. In the case of co-doped cerium and terbium, the excitation spectra of Tb3+ emission in LnMgB,O,,: Ce,Tb consist of a broad band with double peaks. One is the Tb3+ excited peak near 282 nm corresponding to the peak at 244 nm in LnMgB,OlO:Tb. The other peak is the excited Ce3+ peak; this shifts slightly for various matrices. For example, it occurs at 330 nm for
396
lanthanum, at 360 nm for gadolinium and at 366 nm for yttrium respectively. (2) Comparison of the three rare earth matrices for *_ GdMgBSOn-,:Ce,Tb shows that Max In, and XIri, are larger than Max Ice ano Z;lce respectively. Their intensity ratios are several times those of lanthanum and yttrium compounds. Gd3+ may transfer excitation energy from Ce3+ to Tb3+ and intensify the Tb3+ 5D,-7F0 emission. Therefore GdMgB5010:Ce,Tb has the most efficient luminescence with UV-excitation at 254 nm (see Fig. 3), making it an excellent lamp phosphor. The excitation spectra of YMgBSOn,:Ce,Tb are very similar to those of GdMgO,Ois:Ce,Tb. All Mtin,:Maxlc, ratios are larger than 1, but if Ce3+ content is five times greater than Tb3+ content, the ratio of integrated intensity ZZ:In,:Zlce is less than 1, so Tb3+ emission at 542 nm can be obtained; this has maximum brightness with 365 nm UV-excitation (see Fig. 3). In the excitation spectra of LaMgBsOiO:Ce,Tb, the two peaks are close to each other and the ratio of maximum intensity and integrated intensity for both peaks are in reverse order. Monitoring Tb3+ 542 nm emission, the Tb3+ excitation peak is smaller than the Ce3+ excitation peak; thus, among the three matrices, the brightness of the lanthanum compounds is the lowest under short UV-excitation. However, Tb3+ emission in LaMgB,Oi,,:Ce, Tb is not efficient with 365 nm UVexcitation because its excitation peak falls off in intensity at 360 nm. (3) The excitation spectra of binary matrix La-Gd and Y-Gd in LnMgBsO,,:Ce,Tb are very similar. The excitation spectrum of the La-Gd system, for example, is given in Fig. 5. In this case, the excitation peak for Ce3+ almost disappears, but the Tb3+ excitation peak at 284 nm is obviously intensified. This clearly shows that Gd plays the role of available intermediary in the energy migration from Ce3+ to Tb3+. Blasse described [4] the procedure of energy migration in Ce-Gd-Tb. We expect that further study will find the
4.68 X 10’
5.38 X 1OS em=542nm
> E
1 z
c
C
e 8
al
‘;
5
C
C 200.00
285.00 Waveiength (nm)
370.00
200.00
300.00 Wavelength (nm)
Fig. 4. Excitation spectrum of GdMgB~Olo:Tb.
Fig. 5. Excitation spectrum of Tb3+ emission (em = 542 nm) in La~.7~Gd~_~&lgB~0~~: Ce,Tb.
397
most suitable composition for high-efficiency luminescence earth mixtures (dependent on the excitation wavelength This will extend the applications of rare earth luminescence.
using binary rare of the material).
References 1 A. W. Veenis and A. Bril, Philips J. Res., 33 (1978) 124. 2 M. Leskela, M. Saakes and G. Blasse, Mater. Res. Bull., 19 (1984) 151. 3 B. Saubat, C. Fouassier, P. Hagenmuller and J. C. Bonrcet, Mater. (1981) 193. 4 G. Blasse, J. Less-Common Met., 112 (1985) 79. 5 M. Buijs and G. Blasse, J. Lumin., 34 (1986) 236. 6 M. Buijs, J. P. M. Van Vliet and G. Blasse, J. Lumin., 35 (1986) 213.
Res. Bull.,
16