稀土配合物电致发光器件的瞬态特性和红外发光研究
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摘要
三价稀土(RE)配合物作为发光材料在有机电致发光领域独树一帜。这是因为
其具有如下特点:丰富的4f-4f跃迁覆盖从紫外到红外波段,窄谱带的发射有比较好
的色纯度和色饱和度,激发态寿命长,且在有机电致发光(OEL)过程中稀土离子可
以有效利用三线态激子能量发光,因而其电致发光的内量子效率理论上可以达到
100%。这些特点使稀土配合物电致发光在信息显示、光通信和激光输出等领域存在
实际或潜在的应用前景。
本论文的内容大致分为两方面:一是对脉冲电压驱动下的稀土配合物瞬态电致发
光特性进行了研究,得到了一些有意义的结果;二是首次观测到两种稀土离子,即铥
和钬配合物的红外电致发光,并探讨了稀土配合物红外电致发光器件在红外光通讯中
的潜在用途。
首先,我们研究了基于稀土配合物的OEL器件的瞬态电致发光。我们根据两种
稀土配合物Eu(DBM)_3bath[稀土本征发射]和Gd(DBM)_3bath[激基复合物发射
(exciplex)]的不同发光机制,以及它们瞬态电致发光行为的比较,首次较为准确地
测定了一类稀土配合物RE(DBM)_3bath的电子迁移率;半定量地总结了器件中
RE(DBM)_3bath配合物层内部激子复合区域随电场强度的变化规律;分析了EL
器件有机界面两侧贮存的空间电荷再复合导致的电致发光信号的瞬间增强,即
尖峰现象。
第二方面,在稀土红外发射方面,我们首次报道了铥和钬配合物的红外电致
和光致发光。这一发现为未来有机光通信提供了新的材料选择。分析了不同的
配体对Tm~(3+)配合物红外发射的影响,提出在电激发过程中,第一配体(而不是
第二配体)的最低激发三重态(T_1)与受体能级间的距离是RE配合物得到有
效红外发射的关键。首次报道了Ho(DBM)_3bath在光激发和电激发下的1500nm
发射。通过比较可见区Ho~(3+)离子的本征发射和有机界面的激基复合物发射,验
证了器件在不同驱动电压下得激子复合区域的扩展现象。首次得到了发射光谱
随电压变化的电压调制稀土配合物红外电致发光器件,并对现象进行了初步分
析。
Rare earth (RE) complexes used in the field of organic light-emitting diodes (OLED) have attracted much attention because of their narrow-band emissions and miscellaneous luminous properties. Given the complete intersystem crossing from the siglet to triplet and efficient intramolecular energy transfer from triplet to center ions, one can expect excellent performance of RE-complex-containing devices. Therefore, the application of RE complexes into OLED display technology shows satisfied narrow-band emissions covering the whole visible range. Moreover, since the abundant emissions of RE ions in the infrared range, RE complexes become the candidate materials for optical communicationsin the future.For better understanding of the mechanism in the RE complexes-based devices, we investigated the transient behaviors of the common RE complexes devices. On the other hand, electroluminescence (EL) and photoluminescence (PL) properties of new infrared emissive materials, including Tm~3+- and Ho~3+- complexes, were also explored.The electron mobility of tris-(dibenzoylmethanato)-mono-(bathophenanthroline or 1,10-phenonthroline) RE (RE(DBM)_3bath), i.e., 8×10~-5 cm~2/Vs under electric field of 1 MV/cm, was reported for the first time using transient EL measurement. Meanwhile, it was found that the electron mobility of Eu(DBM)3bath was higher than that of Gd(DBM)3bathat same electric field. The superior electron mobility of Eu complex suggested that there existed a considerable part of recombination taking place in bulk layer of RE(DBM)_3bath film which leaded to higher electron mobility which was observed from Eu(DBM)3bath, although principly the mobility of RE(DBM)3bath of different central ions should be same.Besides, we observed a strong EL spike at the end of driving pulse,
which was attributed to recombination of the remaining space charges. This phenomenon will be helpful to realize the electrical pumped Eu(DBM)3bath laser diodes.EL and PL in both visible and near infrared spectral range were observed from a holmium complex, Ho(DBM)3bath, for the first time. Five peaks at 580 nm, 660 nm, 980 nm, 1200 nm and 1500 nm were attributed to the internal 4f electronical transitions of the Ho3+ ion. The 1500 nm infrared emission corresponding to the 5F5—5I6 transition suggests Ho(DBM)3bath a potential candidate for the optical communications.Another type of near infrared OEL devices was also fabricated employing Tm complexes as emitting materials. The EL peaks at 1.4 um and 0.8 um were observed from the devices based on Tm(DBM)3bath or Tm(DBM)3phen at room temperature and were assigned to 3F4—3H4 and 3F4—3H6 transitions of Tm3+ ions, respectively. By comparison with the NIR emissions of four Tm-complexes with different ligands, it was found that the first ligand played a more important role for the Tm3+ ion emissions rather than the second one. Furthermore, in order to meet the requirement of optical communication, both Tm(DBM)3bath and Er(DBM)3bath were incorporated into EL devices so that a broadened EL emission band ranging from 1.4 um to 1.6 um was obtained, showing the potential application of Tm-complexes for optical communication systems.A novel type ofvoltage-tunable infrared emitting device was proposed. There existed two emissive centers in the emission layer and performed an interesting voltage-controlled infrared emission, which could be ascribed to the non-uniform distribution of excitons in the EL device.
其具有如下特点:丰富的4f-4f跃迁覆盖从紫外到红外波段,窄谱带的发射有比较好
的色纯度和色饱和度,激发态寿命长,且在有机电致发光(OEL)过程中稀土离子可
以有效利用三线态激子能量发光,因而其电致发光的内量子效率理论上可以达到
100%。这些特点使稀土配合物电致发光在信息显示、光通信和激光输出等领域存在
实际或潜在的应用前景。
本论文的内容大致分为两方面:一是对脉冲电压驱动下的稀土配合物瞬态电致发
光特性进行了研究,得到了一些有意义的结果;二是首次观测到两种稀土离子,即铥
和钬配合物的红外电致发光,并探讨了稀土配合物红外电致发光器件在红外光通讯中
的潜在用途。
首先,我们研究了基于稀土配合物的OEL器件的瞬态电致发光。我们根据两种
稀土配合物Eu(DBM)_3bath[稀土本征发射]和Gd(DBM)_3bath[激基复合物发射
(exciplex)]的不同发光机制,以及它们瞬态电致发光行为的比较,首次较为准确地
测定了一类稀土配合物RE(DBM)_3bath的电子迁移率;半定量地总结了器件中
RE(DBM)_3bath配合物层内部激子复合区域随电场强度的变化规律;分析了EL
器件有机界面两侧贮存的空间电荷再复合导致的电致发光信号的瞬间增强,即
尖峰现象。
第二方面,在稀土红外发射方面,我们首次报道了铥和钬配合物的红外电致
和光致发光。这一发现为未来有机光通信提供了新的材料选择。分析了不同的
配体对Tm~(3+)配合物红外发射的影响,提出在电激发过程中,第一配体(而不是
第二配体)的最低激发三重态(T_1)与受体能级间的距离是RE配合物得到有
效红外发射的关键。首次报道了Ho(DBM)_3bath在光激发和电激发下的1500nm
发射。通过比较可见区Ho~(3+)离子的本征发射和有机界面的激基复合物发射,验
证了器件在不同驱动电压下得激子复合区域的扩展现象。首次得到了发射光谱
随电压变化的电压调制稀土配合物红外电致发光器件,并对现象进行了初步分
析。
Rare earth (RE) complexes used in the field of organic light-emitting diodes (OLED) have attracted much attention because of their narrow-band emissions and miscellaneous luminous properties. Given the complete intersystem crossing from the siglet to triplet and efficient intramolecular energy transfer from triplet to center ions, one can expect excellent performance of RE-complex-containing devices. Therefore, the application of RE complexes into OLED display technology shows satisfied narrow-band emissions covering the whole visible range. Moreover, since the abundant emissions of RE ions in the infrared range, RE complexes become the candidate materials for optical communicationsin the future.For better understanding of the mechanism in the RE complexes-based devices, we investigated the transient behaviors of the common RE complexes devices. On the other hand, electroluminescence (EL) and photoluminescence (PL) properties of new infrared emissive materials, including Tm~3+- and Ho~3+- complexes, were also explored.The electron mobility of tris-(dibenzoylmethanato)-mono-(bathophenanthroline or 1,10-phenonthroline) RE (RE(DBM)_3bath), i.e., 8×10~-5 cm~2/Vs under electric field of 1 MV/cm, was reported for the first time using transient EL measurement. Meanwhile, it was found that the electron mobility of Eu(DBM)3bath was higher than that of Gd(DBM)3bathat same electric field. The superior electron mobility of Eu complex suggested that there existed a considerable part of recombination taking place in bulk layer of RE(DBM)_3bath film which leaded to higher electron mobility which was observed from Eu(DBM)3bath, although principly the mobility of RE(DBM)3bath of different central ions should be same.Besides, we observed a strong EL spike at the end of driving pulse,
which was attributed to recombination of the remaining space charges. This phenomenon will be helpful to realize the electrical pumped Eu(DBM)3bath laser diodes.EL and PL in both visible and near infrared spectral range were observed from a holmium complex, Ho(DBM)3bath, for the first time. Five peaks at 580 nm, 660 nm, 980 nm, 1200 nm and 1500 nm were attributed to the internal 4f electronical transitions of the Ho3+ ion. The 1500 nm infrared emission corresponding to the 5F5—5I6 transition suggests Ho(DBM)3bath a potential candidate for the optical communications.Another type of near infrared OEL devices was also fabricated employing Tm complexes as emitting materials. The EL peaks at 1.4 um and 0.8 um were observed from the devices based on Tm(DBM)3bath or Tm(DBM)3phen at room temperature and were assigned to 3F4—3H4 and 3F4—3H6 transitions of Tm3+ ions, respectively. By comparison with the NIR emissions of four Tm-complexes with different ligands, it was found that the first ligand played a more important role for the Tm3+ ion emissions rather than the second one. Furthermore, in order to meet the requirement of optical communication, both Tm(DBM)3bath and Er(DBM)3bath were incorporated into EL devices so that a broadened EL emission band ranging from 1.4 um to 1.6 um was obtained, showing the potential application of Tm-complexes for optical communication systems.A novel type ofvoltage-tunable infrared emitting device was proposed. There existed two emissive centers in the emission layer and performed an interesting voltage-controlled infrared emission, which could be ascribed to the non-uniform distribution of excitons in the EL device.
引文
[1] Pioneer News, 1995, Oct. 12.5.
[2] A. Bernnanose, et al, J. Chem. Phys., 32, 396.
[3] M. Pope, et al, J. Chem. Phys., 36 (1963) 2042.
[4] P. S. Vincett, et al, Thin Solid Films, 44 (1982) 171.
[5] C.W. Tang, S. A. Vanslyke, Organic electroluminescent devices, Appl. Phys. Lett. 1987, V51, 913-915
[6] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Markay, R. H. Friend, P. L. Burns, A. B. Holmes, Light-emitting diodes based on conjugated polymers, Nature, 1990, V347, 539-541
[7] D. Brown, A. J. Heeger, Electroluminescence from light-emitting diodes fabricated from conducting polymers, Thin Solid Films, 1992, V216, 96-98
[8] G. Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri, A. J. Heeger, Flexible light-emitting diodes made from soluble conducting polymer, Nature, 1992, V357, 477-479
[9] C. Adachi, M. A. Baldo, S. R. Forrest, M. E. Thompson, High-efficiency organic electrophosphorescent devices with tirs(2-phenylpyridine)iridium doped into elctron-transporting materials, Appl. Phys. Lett. 2000, V77,904-906
[10] P. E. Burrows, S. R. Forrest, T. X. Zhou, L. Michalski, Operating lifetime of phosphorescent organic light emitting devices, Appl. Phys. Lett. 2000, V76, 2493-2495
[11] C. J. Liang, D. Zhao, Z. R. Hong, D. Z. Zhao, X. Y. Liu, W. L. Li, J. B. Peng, J. Q. Yu, C. S. Lee, S. T. Lee, Improved performance of electroluminescent devices based on an europium complex, Appl. Phys. Lett. 2000, V76, 67-69
[12] X. C. Gao, H. Cao, C. H. Huang, B. G. Li, Electroluminescence of a novel terbium complex, Appl. Phys. Lett. 1998, V72, 2217-2219
[13] R. J. Curry, W. P. Gillin, 1.54 μm electroluminescence from erbium (III) tris(8-hydroxyquinoline) (ErQ)-based organic light-emitting diodes, Appl. Phys. Lett. 1999, V75, 1380-1382
[14] Y. Kawamura, Y. Wada, Y. Hasegawa, M. Iwamuro, T. Kitamura, S. Yanagida, Observation of neodymium electroluminescence, Appl. Phys. Lett. 1999, V74, 3245-3247
[15] Y. Kawamura, Y. Wada, M. Iwamuro, T. Kitamura, S. Yanagida, Near-infrared electroluminescence from ytterbium(lll) complex, Chemistry Letters 2000, 280-281
[16] Ziruo Hong, Chunjun Liang, Ruigang Li, Faxin Zang, Di Fan, Wenlian Li, L. S. Hung, S. T. Lee, Infrared and visible emission from organic electroluminescent devices based on praseodymium complex, Appl. Phys. Lett, 2001, V79, 1942-1944.
[2] A. Bernnanose, et al, J. Chem. Phys., 32, 396.
[3] M. Pope, et al, J. Chem. Phys., 36 (1963) 2042.
[4] P. S. Vincett, et al, Thin Solid Films, 44 (1982) 171.
[5] C.W. Tang, S. A. Vanslyke, Organic electroluminescent devices, Appl. Phys. Lett. 1987, V51, 913-915
[6] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Markay, R. H. Friend, P. L. Burns, A. B. Holmes, Light-emitting diodes based on conjugated polymers, Nature, 1990, V347, 539-541
[7] D. Brown, A. J. Heeger, Electroluminescence from light-emitting diodes fabricated from conducting polymers, Thin Solid Films, 1992, V216, 96-98
[8] G. Gustafsson, Y. Cao, G. M. Treacy, F. Klavetter, N. Colaneri, A. J. Heeger, Flexible light-emitting diodes made from soluble conducting polymer, Nature, 1992, V357, 477-479
[9] C. Adachi, M. A. Baldo, S. R. Forrest, M. E. Thompson, High-efficiency organic electrophosphorescent devices with tirs(2-phenylpyridine)iridium doped into elctron-transporting materials, Appl. Phys. Lett. 2000, V77,904-906
[10] P. E. Burrows, S. R. Forrest, T. X. Zhou, L. Michalski, Operating lifetime of phosphorescent organic light emitting devices, Appl. Phys. Lett. 2000, V76, 2493-2495
[11] C. J. Liang, D. Zhao, Z. R. Hong, D. Z. Zhao, X. Y. Liu, W. L. Li, J. B. Peng, J. Q. Yu, C. S. Lee, S. T. Lee, Improved performance of electroluminescent devices based on an europium complex, Appl. Phys. Lett. 2000, V76, 67-69
[12] X. C. Gao, H. Cao, C. H. Huang, B. G. Li, Electroluminescence of a novel terbium complex, Appl. Phys. Lett. 1998, V72, 2217-2219
[13] R. J. Curry, W. P. Gillin, 1.54 μm electroluminescence from erbium (III) tris(8-hydroxyquinoline) (ErQ)-based organic light-emitting diodes, Appl. Phys. Lett. 1999, V75, 1380-1382
[14] Y. Kawamura, Y. Wada, Y. Hasegawa, M. Iwamuro, T. Kitamura, S. Yanagida, Observation of neodymium electroluminescence, Appl. Phys. Lett. 1999, V74, 3245-3247
[15] Y. Kawamura, Y. Wada, M. Iwamuro, T. Kitamura, S. Yanagida, Near-infrared electroluminescence from ytterbium(lll) complex, Chemistry Letters 2000, 280-281
[16] Ziruo Hong, Chunjun Liang, Ruigang Li, Faxin Zang, Di Fan, Wenlian Li, L. S. Hung, S. T. Lee, Infrared and visible emission from organic electroluminescent devices based on praseodymium complex, Appl. Phys. Lett, 2001, V79, 1942-1944.