一种新型铽、钆稀土配合物的发光特性

Emitting Characteristics of a New Rare Earth Complex Doped into Ploy N-vinylcarbazole

合成了一种新型的铽、钆稀土配合物TbGd(BA)6(bipy)2,把它作为发光材料应用于有机电致发光器件中。为改善稀土配合物的载流子传输能力并避免其在真空蒸发时的热分解,实验中将铽、钆稀土配合物TbGd(BA)6(bipy)2掺入高分子导电聚合物Poly(N-vinycarbazole)(PVK)中,用旋涂的方式制备发光层,并制成电致发光器件。通过测量器件的光致和电致发光光谱,均得到纯正的、明亮的Tb3+离子的绿光发射,四个特征峰分别位于489,545,585,620nm,分别对应着能级5D4→7FJ(J=6,5,4,3)的跃迁。讨论了共混体系的发光特性和能量传递机理。稀土配合物的光致发光是由于外部直接激发及PVK到稀土配合物的能量传递。电致发光有两个途径,PVK到稀土配合物的能量传递及载流子的直接俘获。在双层器件中,发光区域随Alq3厚度变化,尤其是在高电压下,激子复合区域移向Alq3一侧。优化后,多层器件在电压为13V时,达到最高亮度183cd/m2,得到明亮的铽的绿色发光。

A new rare earth complex TbGd （BA）6 （bipy）2 was synthesized, which was used as an emitting material in OLEDs. By doping into poly N-vinylearbazole（ PVK）, stability and conductivity of terbium complex are improved. As can be seen from photolumineseence spectra of the blended film, the emission peaks at 405,489, 545, 585, 620 nm respond to PVK and ^5D4→^7FJ （J = 6,5,4,3） transition of Tb^3＋ ions respectively. The photoluminescence of PVK, terbium complex and their co-system indicated that energy transferred from PVK to terbium complex is respected as both the ratio of their blend and the state of terbium complex dispersed into PVK. When the m（ PVK）：m（TbGd（BA） 6 （bipy）2） is 5：1, the energy transferred from PVK to terbium complex completely. In order to study electroluminescence mechanism of the terbium complex, two series devices were fabricated with structures ： （ 1 ） ITO/PVK： TbGd （ BA ） 6 （ bipy ） 2/Al ; （ 2 ） ITO/PVK： TbGd- （BA） 6 （ bipy ） 2/Alq3/LiF/Al. The emitting film was prepared by spin coating PVK： TbGd （ BA ） 6 （ bipy ） 2 chloroform solution with mass ratio 5：1 onto the clean dry ITO glass. Then, the layers of Alq3, LiF and Al were deposited by vacuum deposition. For single-layer and double-layer devices, the emission of PVK is completely restrained, and only the green emission from Tb^3＋ is observed in electroluminescence, which is different from that in photoluminescence. The characteristics of these devices are investigated that not only energy transfer but also direct sequential charge trapping appeared to be the operating mechanism. In the charge trapping process, PVK is a hole transporting material and terbium complexes play a role as electron trapping centers. Terbium complexes trap electrons and holes, which enable direct recombination on terbium complexes. In the double-layer devices, holes and electrons were recombinated at the interface of emitting-layer/ electron-transporting-layer. With increasing the thickness of Alq3, especially at highly electric field, exciton recombination region transferred closely to electron transporting layer. From the optimized double-layer device, bright and green emission from terbium complex had been obtained with the highest brightness of 183 cd/m^2 at 13 V.