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Luminescence properties of complex Tb0.25Eu0.75(TTA)2(N-HPA)Phen
Journal of Alloys and Compounds 468 (2009) 406–409
Luminescence properties of complex Tb0.25Eu0.75(TTA)2(N-HPA)Phen Yuguang Lv a,b , Jingchang Zhang a,∗ , Weiliang Cao a , Yali Fu a , Zhiyue Han a a
Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Beijing 100029, China b College of Chemistry and Pharmacy, Jiamusi University, Jiamusi 154007, China Received 4 November 2007; received in revised form 27 December 2007; accepted 3 January 2008 Available online 6 May 2008
Abstract Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen of Eu3+ with thenoyltrifluoroacetone (HTTA), N-phenylanthranilic acid (N-HPA) and 1,10-phenanthroline (Phen) doped with Tb3+ has been synthesized. Photophysical properties of the complex were studied in detail with IR, DTA–TG, XRD, ultraviolet absorption spectra and fluorescent spectra. The luminescence of Eu3+ complex was enhanced by doping with Tb3+ . It is proved by the TG curve that the complex is stable, and we have monitored the spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen with different ratios for spin-cast film rpm. It was found that there was an efficient energy transfer process between the ligands and metal ions. © 2008 Elsevier B.V. All rights reserved. Keywords: Thin films; Synthesis; Luminescence; Electroluminescence
1. Introduction
2. Experimental details
Lanthanide(III) ions have been regarded as attractive luminescent centers for optical devices, luminescence sensors of chemical species and biomedical assays. Rare earth complexes have good luminescence properties, such as extremely narrow emission bands and high internal quantum efficiencies, which are suitable to use as the emission materials [1–4]. Therefore, many rare earth complexes have been synthesized and used as the emitters in photoluminescence and electroluminescence devices [5–8]. In order to get brighter OEL, two methods can be applied to design luminescent rare earth complexes besides choosing a suitable device structure [9,10]. In this paper, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen has been synthesized to investigate the improvement of the europium emission. We have monitored the spectra of Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen (PVK: Eu/BCP/AlQ/Al) at the different rate rpm. Experimental result shows that the complex has good luminescent properties.
2.1. Sample preparation
∗
Corresponding author. Tel.: +86 10 64434904; fax: +86 10 64434898. E-mail address: [email protected] (J. Zhang).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.01.049
1 mmol mixture of EuCl3 ·6H2 O and TbCl3 ·6H2 O (mole ratios of Eu3+ to are 0.75:0.25), 2 mmol of HTTA and 1 mmol of N-HPA were dissolved in 50 ml ethanol. The pH value of the mixture was adjusted to 6–7 by adding 3 mmol ammonia. Then, Phen in ethanol solution was added to the reaction mixture, the molar ratio of 1,10-phenanthroline to RE3+ ion being 1:1. The precipitate was filtered, washed with water and ethanol, dried at room temperature, and then stored in a silica-gel drier. Tb3+
2.2. Electroluminescence device preparation Here, poly(N-vinylcarbazole) (PVK) was dissolved in chloroform with a concentration of 10 mg/ml. In order to improve the performance of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen thin film, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen was doped into PVK at weight ratio of 1:3. The PVK:Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen thin film was fabricated on the top of cleaned ITO coated glass substrate.
2.3. Measurements The sample solutions for optical measurements were prepared as follows: DTA–TG curves were obtained with a TGA–DTA 1700-Perkin-Elmer. Infrared spectra were recorded in the range of 4000–400 cm−1 by a prostige-21IR spectrophotometer in KBr flake. UV–vis spectra were performed on a UV-2501PCS double spectrophotometer. The excitation and emission spectra measurements were performed on a Shimadzu 5301 spectrofluorophotometer equipped with a 150 W xenon lamp as the excitation source. Spectra were recorded using monochromator slit widths of 1.5 nm on both excitation and emission sides. The
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
407
Fig. 1. DTA–TG plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen. EL spectra were measured by SPEX Fluorolog-3 spectrometer at room temperature. The luminance was measured by PR-650 spectra-scan spectrometer.
Fig. 2. Infrared spectra of ligands and Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen in the range of 4000–400 cm−1 .
DTA–TG plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen are shown in Fig. 1. For example, DTA plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen show endothermic peak (melt-endothermic peak) at 218 ◦ C, but TG plots of the complex did not change. TG curves prove that the complex is stable, ranging from ambient temperature to 218 ◦ C in air. From Table 1, the complex contents (RE2 O3 , %) is not significantly different from the results of calculation according to the formula.
ferences in comparison with the ligands. The peaks around 1539 cm−1 corresponded to a stretching vibration of –N C (1,10-phenanthroline), 858 cm−1 , 721 cm−1 corresponded to a rC–H vibration of 1,10-phenanthroline and the peak in the spectra of complex at about 540 cm−1 reveals the presence of C–O–Ln and it cannot be observed in the ligands. In addition, typical asymmetric vibration of VC O (HTTA) group peaks were detected at about 1603 and 1511 cm−1 . Symmetric and asymmetric vibration of –COO− (N-HPA) group peaks was detected at about 1577 and 1413 cm−1 . IR spectra of doping elements complex was obviously different from HTTA, N-HPA and 1,10phenanthroline ligands. This indicates that were similar to the complex reported before [11,12].
3.2. IR spectra analysis
3.3. UV absorption spectra
FTIR absorption spectra of several ligands and complex are shown in Fig. 2. It can be seen that the absorption bands of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen have shown significant dif-
UV absorption spectra peaks of free ligands and complex in CHCl3 solution are listed in Table 2. Fig. 3 shows a UV spectrum of free ligands and Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen, absorption energy of the complex mostly comes
3. Results and discussion 3.1. DTA–TG analysis
Table 1 DTA–TG peaks of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen Decomposition temperature (◦ C) and weight loss (%) 218 Tm1 (◦ C) Weight loss (%) 0.00 Tm2 (◦ C) Weight loss (%)
544 75.3
RE2 O3 (%)
17.2 (17.8)
Table 2 Major UV absorption peaks of ligands and complex Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen
λ1 (nm) λ2 (nm) λ3 (nm)
HTTA
N-HPA
1,10-Phen
Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen
324.00 344.80 354.80
295.40 357.20 384.80
268.00 291.20 324.50
272.00 340.40 Fig. 3. UV spectra of ligands and Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen.
408
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
3.5. Electroluminescence
Fig. 4. Typical emission spectrum of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen.
from those ligands, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen shows typical absorption peaks of HTTA, N-HPA and 1,10-Phen. 3.4. Fluorescence properties Fluorescence emission spectra of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen is shown in Fig. 4. The corresponding emission spectrum contains 5 D0 → 7 FJ (J = 0, 1, 2, 3, 4) transition lines of Eu3+ , with hypersensitive transition 5 D0 → 7 F2 red emission as the most prominent group.
Fig. 5 shows the electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (PVK: Eu/BCP/AlQ/Al), the spectra of thin films obtained with different spinning rates, where the electroluminescence starts at a forward bias of 10 V. The brightness of the device increases with the increase of the bias voltage. This demonstrates that the electroluminescence is also from Eu3+ of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen in the blend emissive layer, and no electroluminescence is observed from PVK. It shows that the emission of Eu3+ ion owes to energy transferring from PVK. Under forward bias voltage, carriers were injected from electrodes, migrated and recombinated to form excitons in the PVK firstly, since the electron injection and transport property of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen is poor. Then the energy of excitons is transferred to the ligand by radiative decay, and finally to the central Eu ion [13–18]: • Device I: ITO/PVK: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (60 nm)/BCP (10 nm)/Al • Device II: ITO/PVK: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (60 nm)/BCP (10 nm)/Alq3 (8 nm)/Al In the structural device I, the characteristic emissions of europium ions at 594, 615, 655 and 690 nm are obtained under different driving voltage, as shown in Fig. 5. These emission peaks correspond to four energy level transitions of 5 D0 –7 FJ
Fig. 5. Electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (λex = 330 nm).
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
409
used as emission materials. Experimental result shows the complex is stable, and luminescence of Eu3+ complex is enhanced after doping with Tb3+ . Photoluminescence spectra indicate that the complex shows good luminescent properties. The Tb3+ ion acts as an energy transfer bridge that helps energy transfer from PVK to Eu3+ . Acknowledgments This work was supported by research fund for the Doctoral Program of Higher Education (No. 20050010014), National Development Project of High Technology (Project 863) (2006AA03Z 412) and emphasis research fund for Jiamusi University (Szj2008-018). Fig. 6. Electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen at a driving voltage of 16 V.
(J = 1, 2, 3, 4) of europium ion (Eu3+ ), respectively. The 5 D0 –7 F1 is a magnetic dipole transition; 5 D0 –7 FJ is an electric dipole transition whose intensity is sensitive to chemical environment. While the Eu ions are found at symmetrical center, 5 D0 –7 F2 has strong fluorescence emission. The properties of monolayer device at 1000 rpm with impure concentration of 1:5 are the best, and optimum voltage is 18 V. Bright red emission can be obtained from the monolayer device. Fig. 6 shows the emission spectrum of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen film evaporated onto glass substrate (device II). There are three main peaks at 614, 595 and 550 nm. The three main peaks derived from Eu3+ ion, corresponding to transition states of 5 D0 → 7 F3 , 5 D0 → 7 F2 and 5 D0 → 7 F1 , the peak at 614 nm is much stronger than the others. The results demonstrate that in the mixed complexes there is almost no emission seen from Tb, there is an emission enhancement in device II. 4. Conclusion The following conclusions can be drawn from this work: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen has been synthesized and
References [1] J.C.G. B¨unzli, G. Bernardinelli, G. Hopfgartner, A.F. Williams, J. Am. Chem. Soc. 115 (1993) 817–821. [2] J. Kide, H. Hayase, K. Hongawa, et al., J. Appl. Phys. Lett. 65 (1994) 2124–2128. [3] G. Sun, W. Li, Y. Zhao, J. Lumin. 17 (1996) 364–369. [4] Z.-J. Wang, B. Li, Y. Fan, Chin. J. Lumin. 17 (1996) 276–280. [5] D. Fan, B. Chu, W. Li, J. Rare Earth 22 (2004) 334–337. [6] G.-L. Zhong, Y.-L. Wang, C.-K. Shi, Thin Solid Films 385 (2001) 234–238. [7] G.-L. Zhong, Y.-L. Wang, C.-K. Shi, J. Lumin. 99 (2002) 213–217. [8] B.-L. An, Y.-H. Yang, J. Rare Earths 21 (2003) 514–519. [9] Y. Lv, J. Zhang, W. Cao, Y. Whang, Z. Xu, J. Lumin. 128 (2008) 117–122. [10] D.-X. Zhao, W.-L. Li, Z.-R. Hong, J. Lumin. 82 (1999) 105–109. [11] X.-Q. Liang, N. Zeng, J. Guangxi Univ. 26 (2001) 298–302. [12] Y. Liu, C.-F. Ye, G.-D. Qian, J.-R. Qiu, J. Lumin. 118 (2006) 158–162. [13] F.-J. Zhang, Z. Xu, F. Teng, L. Liu, L.-J. Meng, Mater. Sci. Eng. B 123 (1) (2005) 84–89. [14] F.-J. Zhang, Z. Xu, F. Teng, J. Lumin. 117 (2006) 90–95. [15] H. Shen, Z. Xu, J. Rare Earth 21 (2003) 519–523. [16] K. Nakamura, Y. Hasegawa, H. Kawai, N. Yasuda, Y. Wada, S. Yanagida, J. Alloys Compd. 408 (2006) 771–775. [17] K. Manseki, Y. Hasegawa, Y. Wada, S. Yanagida, J. Alloys Compd. 408 (2006) 805–808. [18] Y.-G. Lv, J.-C. Zhang, W.-L. Cao, Y.-L. Fu, J. Alloys Compd. 462 (2008) 153–156.
Luminescence properties of complex Tb0.25Eu0.75(TTA)2(N-HPA)Phen Yuguang Lv a,b , Jingchang Zhang a,∗ , Weiliang Cao a , Yali Fu a , Zhiyue Han a a
Institute of Modern Catalysis, Beijing University of Chemical Technology, State Key Laboratory of Chemical Resource Engineering, Beijing 100029, China b College of Chemistry and Pharmacy, Jiamusi University, Jiamusi 154007, China Received 4 November 2007; received in revised form 27 December 2007; accepted 3 January 2008 Available online 6 May 2008
Abstract Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen of Eu3+ with thenoyltrifluoroacetone (HTTA), N-phenylanthranilic acid (N-HPA) and 1,10-phenanthroline (Phen) doped with Tb3+ has been synthesized. Photophysical properties of the complex were studied in detail with IR, DTA–TG, XRD, ultraviolet absorption spectra and fluorescent spectra. The luminescence of Eu3+ complex was enhanced by doping with Tb3+ . It is proved by the TG curve that the complex is stable, and we have monitored the spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen with different ratios for spin-cast film rpm. It was found that there was an efficient energy transfer process between the ligands and metal ions. © 2008 Elsevier B.V. All rights reserved. Keywords: Thin films; Synthesis; Luminescence; Electroluminescence
1. Introduction
2. Experimental details
Lanthanide(III) ions have been regarded as attractive luminescent centers for optical devices, luminescence sensors of chemical species and biomedical assays. Rare earth complexes have good luminescence properties, such as extremely narrow emission bands and high internal quantum efficiencies, which are suitable to use as the emission materials [1–4]. Therefore, many rare earth complexes have been synthesized and used as the emitters in photoluminescence and electroluminescence devices [5–8]. In order to get brighter OEL, two methods can be applied to design luminescent rare earth complexes besides choosing a suitable device structure [9,10]. In this paper, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen has been synthesized to investigate the improvement of the europium emission. We have monitored the spectra of Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen (PVK: Eu/BCP/AlQ/Al) at the different rate rpm. Experimental result shows that the complex has good luminescent properties.
2.1. Sample preparation
∗
Corresponding author. Tel.: +86 10 64434904; fax: +86 10 64434898. E-mail address: [email protected] (J. Zhang).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.01.049
1 mmol mixture of EuCl3 ·6H2 O and TbCl3 ·6H2 O (mole ratios of Eu3+ to are 0.75:0.25), 2 mmol of HTTA and 1 mmol of N-HPA were dissolved in 50 ml ethanol. The pH value of the mixture was adjusted to 6–7 by adding 3 mmol ammonia. Then, Phen in ethanol solution was added to the reaction mixture, the molar ratio of 1,10-phenanthroline to RE3+ ion being 1:1. The precipitate was filtered, washed with water and ethanol, dried at room temperature, and then stored in a silica-gel drier. Tb3+
2.2. Electroluminescence device preparation Here, poly(N-vinylcarbazole) (PVK) was dissolved in chloroform with a concentration of 10 mg/ml. In order to improve the performance of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen thin film, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen was doped into PVK at weight ratio of 1:3. The PVK:Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen thin film was fabricated on the top of cleaned ITO coated glass substrate.
2.3. Measurements The sample solutions for optical measurements were prepared as follows: DTA–TG curves were obtained with a TGA–DTA 1700-Perkin-Elmer. Infrared spectra were recorded in the range of 4000–400 cm−1 by a prostige-21IR spectrophotometer in KBr flake. UV–vis spectra were performed on a UV-2501PCS double spectrophotometer. The excitation and emission spectra measurements were performed on a Shimadzu 5301 spectrofluorophotometer equipped with a 150 W xenon lamp as the excitation source. Spectra were recorded using monochromator slit widths of 1.5 nm on both excitation and emission sides. The
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
407
Fig. 1. DTA–TG plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen. EL spectra were measured by SPEX Fluorolog-3 spectrometer at room temperature. The luminance was measured by PR-650 spectra-scan spectrometer.
Fig. 2. Infrared spectra of ligands and Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen in the range of 4000–400 cm−1 .
DTA–TG plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen are shown in Fig. 1. For example, DTA plots of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen show endothermic peak (melt-endothermic peak) at 218 ◦ C, but TG plots of the complex did not change. TG curves prove that the complex is stable, ranging from ambient temperature to 218 ◦ C in air. From Table 1, the complex contents (RE2 O3 , %) is not significantly different from the results of calculation according to the formula.
ferences in comparison with the ligands. The peaks around 1539 cm−1 corresponded to a stretching vibration of –N C (1,10-phenanthroline), 858 cm−1 , 721 cm−1 corresponded to a rC–H vibration of 1,10-phenanthroline and the peak in the spectra of complex at about 540 cm−1 reveals the presence of C–O–Ln and it cannot be observed in the ligands. In addition, typical asymmetric vibration of VC O (HTTA) group peaks were detected at about 1603 and 1511 cm−1 . Symmetric and asymmetric vibration of –COO− (N-HPA) group peaks was detected at about 1577 and 1413 cm−1 . IR spectra of doping elements complex was obviously different from HTTA, N-HPA and 1,10phenanthroline ligands. This indicates that were similar to the complex reported before [11,12].
3.2. IR spectra analysis
3.3. UV absorption spectra
FTIR absorption spectra of several ligands and complex are shown in Fig. 2. It can be seen that the absorption bands of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen have shown significant dif-
UV absorption spectra peaks of free ligands and complex in CHCl3 solution are listed in Table 2. Fig. 3 shows a UV spectrum of free ligands and Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen, absorption energy of the complex mostly comes
3. Results and discussion 3.1. DTA–TG analysis
Table 1 DTA–TG peaks of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen Decomposition temperature (◦ C) and weight loss (%) 218 Tm1 (◦ C) Weight loss (%) 0.00 Tm2 (◦ C) Weight loss (%)
544 75.3
RE2 O3 (%)
17.2 (17.8)
Table 2 Major UV absorption peaks of ligands and complex Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen
λ1 (nm) λ2 (nm) λ3 (nm)
HTTA
N-HPA
1,10-Phen
Tb0.25 Eu0.75 (TTA)2 (NHPA)Phen
324.00 344.80 354.80
295.40 357.20 384.80
268.00 291.20 324.50
272.00 340.40 Fig. 3. UV spectra of ligands and Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen.
408
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
3.5. Electroluminescence
Fig. 4. Typical emission spectrum of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen.
from those ligands, Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen shows typical absorption peaks of HTTA, N-HPA and 1,10-Phen. 3.4. Fluorescence properties Fluorescence emission spectra of complex Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen is shown in Fig. 4. The corresponding emission spectrum contains 5 D0 → 7 FJ (J = 0, 1, 2, 3, 4) transition lines of Eu3+ , with hypersensitive transition 5 D0 → 7 F2 red emission as the most prominent group.
Fig. 5 shows the electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (PVK: Eu/BCP/AlQ/Al), the spectra of thin films obtained with different spinning rates, where the electroluminescence starts at a forward bias of 10 V. The brightness of the device increases with the increase of the bias voltage. This demonstrates that the electroluminescence is also from Eu3+ of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen in the blend emissive layer, and no electroluminescence is observed from PVK. It shows that the emission of Eu3+ ion owes to energy transferring from PVK. Under forward bias voltage, carriers were injected from electrodes, migrated and recombinated to form excitons in the PVK firstly, since the electron injection and transport property of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen is poor. Then the energy of excitons is transferred to the ligand by radiative decay, and finally to the central Eu ion [13–18]: • Device I: ITO/PVK: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (60 nm)/BCP (10 nm)/Al • Device II: ITO/PVK: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (60 nm)/BCP (10 nm)/Alq3 (8 nm)/Al In the structural device I, the characteristic emissions of europium ions at 594, 615, 655 and 690 nm are obtained under different driving voltage, as shown in Fig. 5. These emission peaks correspond to four energy level transitions of 5 D0 –7 FJ
Fig. 5. Electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen (λex = 330 nm).
Y. Lv et al. / Journal of Alloys and Compounds 468 (2009) 406–409
409
used as emission materials. Experimental result shows the complex is stable, and luminescence of Eu3+ complex is enhanced after doping with Tb3+ . Photoluminescence spectra indicate that the complex shows good luminescent properties. The Tb3+ ion acts as an energy transfer bridge that helps energy transfer from PVK to Eu3+ . Acknowledgments This work was supported by research fund for the Doctoral Program of Higher Education (No. 20050010014), National Development Project of High Technology (Project 863) (2006AA03Z 412) and emphasis research fund for Jiamusi University (Szj2008-018). Fig. 6. Electroluminescence spectra of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen at a driving voltage of 16 V.
(J = 1, 2, 3, 4) of europium ion (Eu3+ ), respectively. The 5 D0 –7 F1 is a magnetic dipole transition; 5 D0 –7 FJ is an electric dipole transition whose intensity is sensitive to chemical environment. While the Eu ions are found at symmetrical center, 5 D0 –7 F2 has strong fluorescence emission. The properties of monolayer device at 1000 rpm with impure concentration of 1:5 are the best, and optimum voltage is 18 V. Bright red emission can be obtained from the monolayer device. Fig. 6 shows the emission spectrum of Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen film evaporated onto glass substrate (device II). There are three main peaks at 614, 595 and 550 nm. The three main peaks derived from Eu3+ ion, corresponding to transition states of 5 D0 → 7 F3 , 5 D0 → 7 F2 and 5 D0 → 7 F1 , the peak at 614 nm is much stronger than the others. The results demonstrate that in the mixed complexes there is almost no emission seen from Tb, there is an emission enhancement in device II. 4. Conclusion The following conclusions can be drawn from this work: Tb0.25 Eu0.75 (TTA)2 (N-HPA)Phen has been synthesized and
References [1] J.C.G. B¨unzli, G. Bernardinelli, G. Hopfgartner, A.F. Williams, J. Am. Chem. Soc. 115 (1993) 817–821. [2] J. Kide, H. Hayase, K. Hongawa, et al., J. Appl. Phys. Lett. 65 (1994) 2124–2128. [3] G. Sun, W. Li, Y. Zhao, J. Lumin. 17 (1996) 364–369. [4] Z.-J. Wang, B. Li, Y. Fan, Chin. J. Lumin. 17 (1996) 276–280. [5] D. Fan, B. Chu, W. Li, J. Rare Earth 22 (2004) 334–337. [6] G.-L. Zhong, Y.-L. Wang, C.-K. Shi, Thin Solid Films 385 (2001) 234–238. [7] G.-L. Zhong, Y.-L. Wang, C.-K. Shi, J. Lumin. 99 (2002) 213–217. [8] B.-L. An, Y.-H. Yang, J. Rare Earths 21 (2003) 514–519. [9] Y. Lv, J. Zhang, W. Cao, Y. Whang, Z. Xu, J. Lumin. 128 (2008) 117–122. [10] D.-X. Zhao, W.-L. Li, Z.-R. Hong, J. Lumin. 82 (1999) 105–109. [11] X.-Q. Liang, N. Zeng, J. Guangxi Univ. 26 (2001) 298–302. [12] Y. Liu, C.-F. Ye, G.-D. Qian, J.-R. Qiu, J. Lumin. 118 (2006) 158–162. [13] F.-J. Zhang, Z. Xu, F. Teng, L. Liu, L.-J. Meng, Mater. Sci. Eng. B 123 (1) (2005) 84–89. [14] F.-J. Zhang, Z. Xu, F. Teng, J. Lumin. 117 (2006) 90–95. [15] H. Shen, Z. Xu, J. Rare Earth 21 (2003) 519–523. [16] K. Nakamura, Y. Hasegawa, H. Kawai, N. Yasuda, Y. Wada, S. Yanagida, J. Alloys Compd. 408 (2006) 771–775. [17] K. Manseki, Y. Hasegawa, Y. Wada, S. Yanagida, J. Alloys Compd. 408 (2006) 805–808. [18] Y.-G. Lv, J.-C. Zhang, W.-L. Cao, Y.-L. Fu, J. Alloys Compd. 462 (2008) 153–156.