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Luminescence properties of Eu(phen)2Cl3 doped in sol–gel-derived SiO2–PEG matrix
November 2000
Materials Letters 46 Ž2000. 244–247 www.elsevier.comrlocatermatlet
Luminescence properties of Eu žphen /2 Cl 3 doped in sol–gel-derived SiO 2 –PEG matrix X.H. Chuai b, H.J. Zhang a,) , F.Sh. Li a , S.B. Wang b, G.Z. Zhou a a
b
Science and Technology UniÕersity of Beijing, 100081, People’s Republic of China Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 People’s Republic of China Received 13 April 2000; accepted 18 May 2000
Abstract Rare earth complex EuŽphen. 2 Cl 3 was introduced into a SiO 2 –PEG400 hybrid material by a sol–gel method. The result indicated that PolyŽethylene glycol. ŽPEG. could associate with Eu3q and change the surroundings of Eu3q in the hybrid material, greatly improving the decay time. Transparent SiO 2 –PEG400 hybrid doped with a very small amount of EuŽphen. 2 Cl 3 has better mechanical properties and can retain excellent luminescence properties of the rare earth complex. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Rare earth complex; EuŽphen. 2 Cl 3 ; Sol–gel; PEG; Luminescence
1. Introduction Many rare earth complexes can emit strong light because of the antenna effect. They have been introduced into SiO 2 matrices by a sol–gel method, greatly improving the thermal and optical stability w1,2x. However, the radiative transition of rare earth ions incorporated into matrices of sol–gel-derived SiO 2 can be quenched due to coupling with the vibrations of their environments, in particular, with the OH group of Si–OH or H 2 O. EuŽphen.2 Cl 3 P 2H 2 O is a good luminescent material, but unfortunately, the water of crystallization may partially quench the luminescence of Eu3q. PolyŽethylene gly-
col. ŽPEG., as a hard Lewis base, can associate with hard acid rare earth ions w3x. Bekiari et al. w4x reported that the presence of PEG200 in the Eu3qdoped SiO 2 gel prevented the quenching of the emission of the Eu3q ion, decreased the spectral width and increased the decay time as well as the emission intensity of Eu3q. We have codoped rare earth complex EuŽphen. 2 Cl 3 with PEG400 into SiO 2 by a sol–gel method to investigate how PEG affects the luminescence properties of EuŽphen. 2 Cl 3 doped in a SiO 2 matrix. 2. Experimental 2.1. Preparation of sample
)
Corresponding author. Tel.: q86-431-568-2801; fax: q86431-569-8041. E-mail address: [email protected] ŽH.J. Zhang..
Tetraethoxysilane ŽTEOS. was hydrolyzed by mixing TEOS with ethanol and acidified water at
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 1 7 9 - 8
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
245
Fig. 1. IR spectrum of the hybrid material doped with EuŽphen. 2 Cl 3 .
molar ratio 1:2:4, then PEG and rare earth complex EuŽphen. 2 Cl 3 dissolved in DMF were added. After the precursor was stirred homogeneously, it was poured into a plastic box, kept covered and aged at 408C for 20 days. The precursor was solidified and wet gel was formed, then a few pinholes were punched in the cover to allow the organic solvates to evaporate. After a week, a monolithic, transparent SiO 2 –PEG400 hybrid material was obtained. 2.2. Spectroscopy measurements The excitation and emission spectra were obtained on a SPEX FL-2T2 spectrofluorimeter with the excitation and emission slit at 1.0 mm and equipped with 450 W lamp as excitation source. Luminescence lifetime was obtained with a SPEX 1934D phosphorimeter using a 7 W xenon lamp as the excitation source Žpulse widths 1 ms.. Infrared ŽIR. spectra were obtained in 400–4000 cmy1 region using a
Perkin-Elmer 58013 IR spectrophotometer with KBr pellet technique.
3. Result and discussion The IR spectrum of the hybrid material is shown in Fig. 1. The main absorption bands and characteris-
Table 1 Main IR absorption bands and characteristic groups of SiO 2 areogel Absorption Assignment frequency Žcmy1 . 3396 1390 1180 457
Absorption Assignment frequency Žcmy1 .
n OH of 1088 adsorbed water ns CH 3 955 ns Si – O – Si 803 d O – Si – O
nas Si – O – Si nas Si – OH d Si – O – Si
246
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
tic vibration modes of groups are summarized in Table 1. A C–O–C asymmetric stretching vibration band was superimposed on the SiO 2 spectra and the sym-
metric stretching band showed a red shift from 2872 to 2931 cmy1 . This resulted from the association of PEG with Eu3q w5x. Aside from the characteristic bands of silica xerogel, SiO 2 –PEGrEuŽphen. 2 Cl 3
Fig. 2. Fluorescence spectra of EuŽphen. 2 Cl 3 pure powder Ža. and doped in SiO 2 –PEG Žb..
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
247
Fig. 3. Fluorescence decay curves of EuŽphen. 2 Cl 3 pure powder Ža. and doped in SiO 2 –PEG hybrid material Žb..
contained additional absorption peak at 1595 cmy1 from the C5N stretching vibration of EuŽphen. 2 Cl 3 . This indicates that EuŽphen. 2 Cl 3 exists in the hybrid material and has an association with PEG. SiO 2 –13 wt.% PEG400 hybrid doped with 0.3 atm% EuŽphen. 2 Cl 3 emits strong red light under the excitation of UV. Fig. 2 shows the excitation spectra of EuŽphen. 2 Cl 3 pure powder Ža. and doped in hybrid material Žb.. The two broad excitation bands show that the red emission originates from phen to Eu3q ion intramolecule energy transfer. The strongest excitation positions can be observed at about 345 and 338 nm, respectively. Both samples have the characteristic emission bands of 5 D 0 – 7 FJ Ž J s 0, 1, 2, 3, 4. transitions of Eu3q. EuŽphen. 2 Cl 3 pure powder has the strongest emission peak at 616 nm with a split, while the emission position of the SiO 2 –PEG400 doped with EuŽphen. 2 Cl 3 has a small blue shift, from 616 to 612 nm, and is inhomogeneously widened. Interestingly, the decay profiles of the 5 D 0 – 7 F2 transition shown in Fig. 3 are greatly different. For pure EuŽphen. 2 Cl 3 powder, the fluorescent intensity reaches a maxim at the beginning, while it decreased with time for EuŽphen. 2 Cl 3 doped in hybrid material. The decay time is 0.8 and 1.7 ms,
respectively. It is possible that this difference is related to the surroundings of Eu3q and the dynamics of intramolecule energy transfer. Detailed experiments are being carried out.
Acknowledgements We acknowledge financial aid from A973B — National Key Project for Fundamental Research of Rare Earth Functional Materials; National Noble Youth Sciences Foundation of China ŽNo. 29225102.; National Natural Science Foundation of China ŽNo. 29731010, No. 29971030..
References w1x L.R. Matthews, X.J. Wang, E.T. Knobbe, J. Non-Cryst. Solids 178 Ž1994. 44. w2x T. Jin et al., J. Electrochem. Soc. 142 Ž10. Ž1995. L195. w3x V. Bekian, P. Lianos, Adv. Mater. 10 Ž17. Ž1998. 1455. w4x V. Bekiari, G. Pistolis, P. Lianos, J. Non-Cryst. Solids 226 Ž1998. 200. w5x W.Y. Xu et al., J. Funct. Polym. 3 Ž1989. 184 Žin Chinese..
Materials Letters 46 Ž2000. 244–247 www.elsevier.comrlocatermatlet
Luminescence properties of Eu žphen /2 Cl 3 doped in sol–gel-derived SiO 2 –PEG matrix X.H. Chuai b, H.J. Zhang a,) , F.Sh. Li a , S.B. Wang b, G.Z. Zhou a a
b
Science and Technology UniÕersity of Beijing, 100081, People’s Republic of China Key Laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 People’s Republic of China Received 13 April 2000; accepted 18 May 2000
Abstract Rare earth complex EuŽphen. 2 Cl 3 was introduced into a SiO 2 –PEG400 hybrid material by a sol–gel method. The result indicated that PolyŽethylene glycol. ŽPEG. could associate with Eu3q and change the surroundings of Eu3q in the hybrid material, greatly improving the decay time. Transparent SiO 2 –PEG400 hybrid doped with a very small amount of EuŽphen. 2 Cl 3 has better mechanical properties and can retain excellent luminescence properties of the rare earth complex. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Rare earth complex; EuŽphen. 2 Cl 3 ; Sol–gel; PEG; Luminescence
1. Introduction Many rare earth complexes can emit strong light because of the antenna effect. They have been introduced into SiO 2 matrices by a sol–gel method, greatly improving the thermal and optical stability w1,2x. However, the radiative transition of rare earth ions incorporated into matrices of sol–gel-derived SiO 2 can be quenched due to coupling with the vibrations of their environments, in particular, with the OH group of Si–OH or H 2 O. EuŽphen.2 Cl 3 P 2H 2 O is a good luminescent material, but unfortunately, the water of crystallization may partially quench the luminescence of Eu3q. PolyŽethylene gly-
col. ŽPEG., as a hard Lewis base, can associate with hard acid rare earth ions w3x. Bekiari et al. w4x reported that the presence of PEG200 in the Eu3qdoped SiO 2 gel prevented the quenching of the emission of the Eu3q ion, decreased the spectral width and increased the decay time as well as the emission intensity of Eu3q. We have codoped rare earth complex EuŽphen. 2 Cl 3 with PEG400 into SiO 2 by a sol–gel method to investigate how PEG affects the luminescence properties of EuŽphen. 2 Cl 3 doped in a SiO 2 matrix. 2. Experimental 2.1. Preparation of sample
)
Corresponding author. Tel.: q86-431-568-2801; fax: q86431-569-8041. E-mail address: [email protected] ŽH.J. Zhang..
Tetraethoxysilane ŽTEOS. was hydrolyzed by mixing TEOS with ethanol and acidified water at
00167-577Xr00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 0 . 0 0 1 7 9 - 8
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
245
Fig. 1. IR spectrum of the hybrid material doped with EuŽphen. 2 Cl 3 .
molar ratio 1:2:4, then PEG and rare earth complex EuŽphen. 2 Cl 3 dissolved in DMF were added. After the precursor was stirred homogeneously, it was poured into a plastic box, kept covered and aged at 408C for 20 days. The precursor was solidified and wet gel was formed, then a few pinholes were punched in the cover to allow the organic solvates to evaporate. After a week, a monolithic, transparent SiO 2 –PEG400 hybrid material was obtained. 2.2. Spectroscopy measurements The excitation and emission spectra were obtained on a SPEX FL-2T2 spectrofluorimeter with the excitation and emission slit at 1.0 mm and equipped with 450 W lamp as excitation source. Luminescence lifetime was obtained with a SPEX 1934D phosphorimeter using a 7 W xenon lamp as the excitation source Žpulse widths 1 ms.. Infrared ŽIR. spectra were obtained in 400–4000 cmy1 region using a
Perkin-Elmer 58013 IR spectrophotometer with KBr pellet technique.
3. Result and discussion The IR spectrum of the hybrid material is shown in Fig. 1. The main absorption bands and characteris-
Table 1 Main IR absorption bands and characteristic groups of SiO 2 areogel Absorption Assignment frequency Žcmy1 . 3396 1390 1180 457
Absorption Assignment frequency Žcmy1 .
n OH of 1088 adsorbed water ns CH 3 955 ns Si – O – Si 803 d O – Si – O
nas Si – O – Si nas Si – OH d Si – O – Si
246
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
tic vibration modes of groups are summarized in Table 1. A C–O–C asymmetric stretching vibration band was superimposed on the SiO 2 spectra and the sym-
metric stretching band showed a red shift from 2872 to 2931 cmy1 . This resulted from the association of PEG with Eu3q w5x. Aside from the characteristic bands of silica xerogel, SiO 2 –PEGrEuŽphen. 2 Cl 3
Fig. 2. Fluorescence spectra of EuŽphen. 2 Cl 3 pure powder Ža. and doped in SiO 2 –PEG Žb..
X.H. Chuai et al.r Materials Letters 46 (2000) 244–247
247
Fig. 3. Fluorescence decay curves of EuŽphen. 2 Cl 3 pure powder Ža. and doped in SiO 2 –PEG hybrid material Žb..
contained additional absorption peak at 1595 cmy1 from the C5N stretching vibration of EuŽphen. 2 Cl 3 . This indicates that EuŽphen. 2 Cl 3 exists in the hybrid material and has an association with PEG. SiO 2 –13 wt.% PEG400 hybrid doped with 0.3 atm% EuŽphen. 2 Cl 3 emits strong red light under the excitation of UV. Fig. 2 shows the excitation spectra of EuŽphen. 2 Cl 3 pure powder Ža. and doped in hybrid material Žb.. The two broad excitation bands show that the red emission originates from phen to Eu3q ion intramolecule energy transfer. The strongest excitation positions can be observed at about 345 and 338 nm, respectively. Both samples have the characteristic emission bands of 5 D 0 – 7 FJ Ž J s 0, 1, 2, 3, 4. transitions of Eu3q. EuŽphen. 2 Cl 3 pure powder has the strongest emission peak at 616 nm with a split, while the emission position of the SiO 2 –PEG400 doped with EuŽphen. 2 Cl 3 has a small blue shift, from 616 to 612 nm, and is inhomogeneously widened. Interestingly, the decay profiles of the 5 D 0 – 7 F2 transition shown in Fig. 3 are greatly different. For pure EuŽphen. 2 Cl 3 powder, the fluorescent intensity reaches a maxim at the beginning, while it decreased with time for EuŽphen. 2 Cl 3 doped in hybrid material. The decay time is 0.8 and 1.7 ms,
respectively. It is possible that this difference is related to the surroundings of Eu3q and the dynamics of intramolecule energy transfer. Detailed experiments are being carried out.
Acknowledgements We acknowledge financial aid from A973B — National Key Project for Fundamental Research of Rare Earth Functional Materials; National Noble Youth Sciences Foundation of China ŽNo. 29225102.; National Natural Science Foundation of China ŽNo. 29731010, No. 29971030..
References w1x L.R. Matthews, X.J. Wang, E.T. Knobbe, J. Non-Cryst. Solids 178 Ž1994. 44. w2x T. Jin et al., J. Electrochem. Soc. 142 Ž10. Ž1995. L195. w3x V. Bekian, P. Lianos, Adv. Mater. 10 Ž17. Ž1998. 1455. w4x V. Bekiari, G. Pistolis, P. Lianos, J. Non-Cryst. Solids 226 Ž1998. 200. w5x W.Y. Xu et al., J. Funct. Polym. 3 Ž1989. 184 Žin Chinese..