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Luminescence of Tb3+ and Eu3+ doped amorphous zinc benzoates
Spectrochimica Acta Part A 59 (2003) 729 /731 www.elsevier.com/locate/saa
Luminescence of Tb3 and Eu3 doped amorphous zinc benzoates Liangjie Yuan, Jutang Sun *, Keli Zhang Department of Chemistry, Wuhan University, Wuhan 430072, People’s Republic of China Received 2 May 2002; accepted 6 June 2002
Abstract The Tb3 and Eu3 doped amorphous zinc benzoate were prepared. Their infrared absorption, emission and excitation spectra were measured. The luminescence mechanisms of Tb3 and Eu3 in the amorphous substrate were discussed. The bonding modes of OCO group to Zn2 ion have two of symmetric and asymmetric bridging bidentate. The energy of the S1 p,p* excited state of benzene ring can be transferred to Tb3 and Eu3 ion, and results in characteristic emission from the 5D4 0/7Fj of Tb3 and 5D0 0/7Fj of Eu3 , respectively. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Luminescence; Zinc; Benzoate; Terbium; Europium
1. Introduction It is well known that rare earth ions have characteristic emission and excellent optical properties, therefore, as activators of luminescence, rare earth ions are doped into inorganic compounds. The rare earth ions doped fluorophosphate, fluoroaluminate and chalcogenide have been studied extensively [1 /3]. In metallorganic compounds containing rare earth ions, organic ligands can transfer the energy that they absorbed in the ultraviolet region to rare earth ions and increase the luminescence intensity of rare earth ions greatly [4 /6]. However, the rare earth ion * Corresponding author. Tel.: /86-27-8721-8494; fax: /8627-8764-7617 E-mail address: [email protected] (J. Sun).
doped amorphous metallorganic substrates have not been reported. To prepare amorphous metallorganic luminescent materials, in this paper, the Tb3 and Eu3 doped amorphous zinc benzoate substrate materials were prepared, and the emission and excitation spectra were measured.
2. Experimental Terbium carbonate was prepared in our laboratory, and all other reagents were of analytical reagent grade. As literature [7] mentioned, a rheological body was obtained from benzoic, zinc oxide, terbium carbonate and proper amount of pure water. The precursor of Tb3 doped amorphous zinc benzoate [Zn(Bzo)2:Tbx , X /0.01 /0.1, Bzo /C6H5COO ] were synthesized from the
1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 2 2 7 - 5
L. Yuan et al. / Spectrochimica Acta Part A 59 (2003) 729 /731
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rheological bodies in a closed container at 70/ 90 8C for 2 h, and dried at 120 8C. With the same method, the precursor of Eu3 doped amorphous zinc benzoate Zn(Bzo)2:Eu0.05 was synthesized from benzoic, zinc oxide and europium oxide in 2:1:0.05 mole ratio. Tb3 and Eu3 doped amorphous zinc benzoate were prepared by melting the precursors at 340 /360 8C and cooled immediately in a copper plate to room temperature. The powder X-ray diffraction (XRD) data of samples loaded onto metal aluminium slides were examined by Shimadzu XRD 6000 diffractometer ˚ ) at 40 kV and with Cu Ka1 radiation (l /1.5405 A 40 mA from 5/308 (2u), at the scan speed of (2u ) 28/min. The FT-IR of the samples was measured on Thermo Nicolet Avatar 360 FT-IR instrument with KBr pellets from 4000 to 400 cm 1at the ambient temperature. The room temperature excitation and emission spectra were examined with RF-5301PC spectrofluorophotometer (Shimadzu) in the range of 200 /700 nm, and the excitation wavelength for the emission was 293 nm for each of the samples in this study.
3. Results and discussion The XRD patterns of Tb3 doped zinc benzoate prepared at 340/3608C are the same as that of Eu3 doped zinc benzoate. Fig. 1 shows the XRD pattern of Tb3 doped zinc benzoate. Two broad diffraction peaks appeared at 7.7 and 18.6(2u), respectively. It is indicated that the structure of samples are amorphous.
Fig. 1. The XRD pattern of Zn(Bzo)2:Tb0.02.
In the IR absorption spectrum of the amorphous Zn(Bzo)2:Tb0.01, the absorption bands at 1597, 1577, 1493 cm 1 are assigned to stretching vibration of C /C of benzene ring, the absorption band at 1417 cm 1 is assigned to the symmetric stretching vibration (ns), and those at 1640 and 1531 cm 1 to the asymmetric stretching vibrations (nas) of the OCO group. The magnitudes of the asymmetric and symmetric bands (nas /ns) of the COO group suggest that there are two modes of coordination, symmetrical and asymmetrical bidentate bridging between carboxylate group and Zn2 ion in the amorphous substrates [8]. The excitation and emission spectra of amorphous Zn(Bzo)2:Tb0.02 are shown in Fig. 2. The 5 D4 0/7Fj (j /6, 5, 4, 3) transition emission of Tb3 are only observed at 488, 542, 582, 618 nm, and the emission from the 5D4 0/7F5 was the strongest. The 5D3 0/7Fj emission of Tb3 ion cannot be observed. The excitation band of Tb3 emission at 293 nm corresponds to the S1 p,p* excitation state resulted from the p,p* transition excitation of benzene ring. The emission intensity of the 5D4 0/7F5 versus doping concentration of Tb3 ions in amorphous Zn(Bzo):Tb is shown in Fig. 3. With an increase of concentration of Tb3, the emission bands of Tb3 are not changed, the emission intensity increases, but when the doped Tb3 concentration was about 2 mol%, the relative intensity is the highest. The amorphous Zn(Bzo)2:Eu0.05 has a red emission when excited by 293 nm UV light. The excitation and emission spectra are shown in Fig. 4. There are only two transition emission bands of
Fig. 2. Excitation (1, lem /542 nm) and emission (2, lex / 293nm) spectra of amorphous Zn(Bzo)2:Tb0.02.
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nonradiatively relaxed to the 5D4 to produce the D4 0/7Fj transition emission of Tb3. But in this amorphous state, because a more stable plane conjugated system cannot form between C6H5COO (Bzo) and metal ions, the energy of the S1 p,p* excited state cannot be effectively transferred very far through the metal/oxygen bonding chains. Therefore, the luminescence intensity of Tb3 in the Zn(Bzo)2 was weaker than that in phthalate for the same mole fraction of Tb3 ion [9]. In the amorphous Zn(Bzo)2:Eu0.05, the energy of the 5D0 0/7Fj transition emission of Eu3 resulted from that of the S1 p,p* excited state of Bzo. 5
Fig. 3. Emission intensity of 5D4 0/7F5 versus concentration of Tb3 ions in amorphous Zn(Bzo)2:Tb excited by 293 nm.
Acknowledgements We are grateful to the National Natural Science Foundation Commission of China.
References Fig. 4. Excitation (1, lem /612 nm) and emission (2, lex / 293nm) spectra of amorphous Zn(Bzo)2:Eu0.05.
Eu3 ion at 590 and 612 nm; one is 5D0 0/7F1 and the other 5D0 0/7F2. The excitation band at 293 nm is consistent with that of amorphous Tb-doped zinc benzoate. Meanwhile, the stimulated excitation bands appeared from 396 to 468 nm are assigned to the 7F0 0/5L56 D2 transition of Eu3 ion. The other excitation bands of Eu3 maybe interoverlap the p 0/p* transition excitation band in benzene ring. The energy transfer and luminescence mechanism in the amorphous Zn(Bzo)2:Tb is proposed as follows: The energy of the S1 p,p* excited state of benzene ring can be directly transferred to the 5Hj of Tb3 ion, and relaxed to the 5D3, then
[1] J.L. Adam, V. Poncon, J. Lucas, G. Boulon, J. Non-Cryst. Solids 91 (1987) 191. [2] A. Belykh, L. Glebov, C. Lerminiaux, S. Lunter, M. Mikhailov, A. Plyukhin, M. Prassas, A. Przhevuskii, J. Non-Cryst. Solids 213/214 (1997) 238. [3] H. Yin, P. Deng, J. Zhang, F. Gan, J. Non-Cryst. Solids 210 (1997) 243. [4] W. Li, W. Li, G. Yu, Q. Wang, R. Jin, J. Alloys Comp. 192 (1 /2) (1993) 34. [5] A. Edwards, C. Claude, I. Sokolik, T.Y. Chu, Y. Okamoto, R. Dorsinville, J. Appl. Phys. 82 (4) (1997) 1841. [6] L. Yuan, J. Sun, K. Zhang, Spectrochim. Acta Part A 55 (1999) 1193. [7] J. Sun, W. Xie, L. Yuan, K. Zhang, Materials Sci. Eng. B64 (1999) 157. [8] G.A. Guseinov, F.N. Musaev, B.T. Usubaliev, I.R. Amiraslanov, K.S. Momedov, Koord. Khim. 10 (1) (1984) 117. [9] Q. Wang, D. Wang, M. Ren, J. Sun, J. Chin. Inorg. Mater. 13 (2) (1998) 152.
Luminescence of Tb3 and Eu3 doped amorphous zinc benzoates Liangjie Yuan, Jutang Sun *, Keli Zhang Department of Chemistry, Wuhan University, Wuhan 430072, People’s Republic of China Received 2 May 2002; accepted 6 June 2002
Abstract The Tb3 and Eu3 doped amorphous zinc benzoate were prepared. Their infrared absorption, emission and excitation spectra were measured. The luminescence mechanisms of Tb3 and Eu3 in the amorphous substrate were discussed. The bonding modes of OCO group to Zn2 ion have two of symmetric and asymmetric bridging bidentate. The energy of the S1 p,p* excited state of benzene ring can be transferred to Tb3 and Eu3 ion, and results in characteristic emission from the 5D4 0/7Fj of Tb3 and 5D0 0/7Fj of Eu3 , respectively. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Luminescence; Zinc; Benzoate; Terbium; Europium
1. Introduction It is well known that rare earth ions have characteristic emission and excellent optical properties, therefore, as activators of luminescence, rare earth ions are doped into inorganic compounds. The rare earth ions doped fluorophosphate, fluoroaluminate and chalcogenide have been studied extensively [1 /3]. In metallorganic compounds containing rare earth ions, organic ligands can transfer the energy that they absorbed in the ultraviolet region to rare earth ions and increase the luminescence intensity of rare earth ions greatly [4 /6]. However, the rare earth ion * Corresponding author. Tel.: /86-27-8721-8494; fax: /8627-8764-7617 E-mail address: [email protected] (J. Sun).
doped amorphous metallorganic substrates have not been reported. To prepare amorphous metallorganic luminescent materials, in this paper, the Tb3 and Eu3 doped amorphous zinc benzoate substrate materials were prepared, and the emission and excitation spectra were measured.
2. Experimental Terbium carbonate was prepared in our laboratory, and all other reagents were of analytical reagent grade. As literature [7] mentioned, a rheological body was obtained from benzoic, zinc oxide, terbium carbonate and proper amount of pure water. The precursor of Tb3 doped amorphous zinc benzoate [Zn(Bzo)2:Tbx , X /0.01 /0.1, Bzo /C6H5COO ] were synthesized from the
1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 2 2 7 - 5
L. Yuan et al. / Spectrochimica Acta Part A 59 (2003) 729 /731
730
rheological bodies in a closed container at 70/ 90 8C for 2 h, and dried at 120 8C. With the same method, the precursor of Eu3 doped amorphous zinc benzoate Zn(Bzo)2:Eu0.05 was synthesized from benzoic, zinc oxide and europium oxide in 2:1:0.05 mole ratio. Tb3 and Eu3 doped amorphous zinc benzoate were prepared by melting the precursors at 340 /360 8C and cooled immediately in a copper plate to room temperature. The powder X-ray diffraction (XRD) data of samples loaded onto metal aluminium slides were examined by Shimadzu XRD 6000 diffractometer ˚ ) at 40 kV and with Cu Ka1 radiation (l /1.5405 A 40 mA from 5/308 (2u), at the scan speed of (2u ) 28/min. The FT-IR of the samples was measured on Thermo Nicolet Avatar 360 FT-IR instrument with KBr pellets from 4000 to 400 cm 1at the ambient temperature. The room temperature excitation and emission spectra were examined with RF-5301PC spectrofluorophotometer (Shimadzu) in the range of 200 /700 nm, and the excitation wavelength for the emission was 293 nm for each of the samples in this study.
3. Results and discussion The XRD patterns of Tb3 doped zinc benzoate prepared at 340/3608C are the same as that of Eu3 doped zinc benzoate. Fig. 1 shows the XRD pattern of Tb3 doped zinc benzoate. Two broad diffraction peaks appeared at 7.7 and 18.6(2u), respectively. It is indicated that the structure of samples are amorphous.
Fig. 1. The XRD pattern of Zn(Bzo)2:Tb0.02.
In the IR absorption spectrum of the amorphous Zn(Bzo)2:Tb0.01, the absorption bands at 1597, 1577, 1493 cm 1 are assigned to stretching vibration of C /C of benzene ring, the absorption band at 1417 cm 1 is assigned to the symmetric stretching vibration (ns), and those at 1640 and 1531 cm 1 to the asymmetric stretching vibrations (nas) of the OCO group. The magnitudes of the asymmetric and symmetric bands (nas /ns) of the COO group suggest that there are two modes of coordination, symmetrical and asymmetrical bidentate bridging between carboxylate group and Zn2 ion in the amorphous substrates [8]. The excitation and emission spectra of amorphous Zn(Bzo)2:Tb0.02 are shown in Fig. 2. The 5 D4 0/7Fj (j /6, 5, 4, 3) transition emission of Tb3 are only observed at 488, 542, 582, 618 nm, and the emission from the 5D4 0/7F5 was the strongest. The 5D3 0/7Fj emission of Tb3 ion cannot be observed. The excitation band of Tb3 emission at 293 nm corresponds to the S1 p,p* excitation state resulted from the p,p* transition excitation of benzene ring. The emission intensity of the 5D4 0/7F5 versus doping concentration of Tb3 ions in amorphous Zn(Bzo):Tb is shown in Fig. 3. With an increase of concentration of Tb3, the emission bands of Tb3 are not changed, the emission intensity increases, but when the doped Tb3 concentration was about 2 mol%, the relative intensity is the highest. The amorphous Zn(Bzo)2:Eu0.05 has a red emission when excited by 293 nm UV light. The excitation and emission spectra are shown in Fig. 4. There are only two transition emission bands of
Fig. 2. Excitation (1, lem /542 nm) and emission (2, lex / 293nm) spectra of amorphous Zn(Bzo)2:Tb0.02.
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nonradiatively relaxed to the 5D4 to produce the D4 0/7Fj transition emission of Tb3. But in this amorphous state, because a more stable plane conjugated system cannot form between C6H5COO (Bzo) and metal ions, the energy of the S1 p,p* excited state cannot be effectively transferred very far through the metal/oxygen bonding chains. Therefore, the luminescence intensity of Tb3 in the Zn(Bzo)2 was weaker than that in phthalate for the same mole fraction of Tb3 ion [9]. In the amorphous Zn(Bzo)2:Eu0.05, the energy of the 5D0 0/7Fj transition emission of Eu3 resulted from that of the S1 p,p* excited state of Bzo. 5
Fig. 3. Emission intensity of 5D4 0/7F5 versus concentration of Tb3 ions in amorphous Zn(Bzo)2:Tb excited by 293 nm.
Acknowledgements We are grateful to the National Natural Science Foundation Commission of China.
References Fig. 4. Excitation (1, lem /612 nm) and emission (2, lex / 293nm) spectra of amorphous Zn(Bzo)2:Eu0.05.
Eu3 ion at 590 and 612 nm; one is 5D0 0/7F1 and the other 5D0 0/7F2. The excitation band at 293 nm is consistent with that of amorphous Tb-doped zinc benzoate. Meanwhile, the stimulated excitation bands appeared from 396 to 468 nm are assigned to the 7F0 0/5L56 D2 transition of Eu3 ion. The other excitation bands of Eu3 maybe interoverlap the p 0/p* transition excitation band in benzene ring. The energy transfer and luminescence mechanism in the amorphous Zn(Bzo)2:Tb is proposed as follows: The energy of the S1 p,p* excited state of benzene ring can be directly transferred to the 5Hj of Tb3 ion, and relaxed to the 5D3, then
[1] J.L. Adam, V. Poncon, J. Lucas, G. Boulon, J. Non-Cryst. Solids 91 (1987) 191. [2] A. Belykh, L. Glebov, C. Lerminiaux, S. Lunter, M. Mikhailov, A. Plyukhin, M. Prassas, A. Przhevuskii, J. Non-Cryst. Solids 213/214 (1997) 238. [3] H. Yin, P. Deng, J. Zhang, F. Gan, J. Non-Cryst. Solids 210 (1997) 243. [4] W. Li, W. Li, G. Yu, Q. Wang, R. Jin, J. Alloys Comp. 192 (1 /2) (1993) 34. [5] A. Edwards, C. Claude, I. Sokolik, T.Y. Chu, Y. Okamoto, R. Dorsinville, J. Appl. Phys. 82 (4) (1997) 1841. [6] L. Yuan, J. Sun, K. Zhang, Spectrochim. Acta Part A 55 (1999) 1193. [7] J. Sun, W. Xie, L. Yuan, K. Zhang, Materials Sci. Eng. B64 (1999) 157. [8] G.A. Guseinov, F.N. Musaev, B.T. Usubaliev, I.R. Amiraslanov, K.S. Momedov, Koord. Khim. 10 (1) (1984) 117. [9] Q. Wang, D. Wang, M. Ren, J. Sun, J. Chin. Inorg. Mater. 13 (2) (1998) 152.