磁场作用下的有机电致发光

Effects of magnetic field on organic electroluminescence

分别制备了荧光器件ITO/NPB/Alq3/LiF/Al和磷光器件ITO/NPB/CBP:Ir(ppy)3/BCP/Alq3/LiF/Al,测试了50mT磁场作用下器件的I-V和L-V特性.与零磁场相比荧光器件和磷光器件的效率分别增加了4.4%和7%.从有机电致发光的机制出发对该现象进行了解释,认为外加磁场可以使三重态激子发生塞曼分裂,进而在荧光器件中引起了三重态激子T+到单重态激子S的转化;磷光器件中增大了主体向客体的三重态能量传递速率.磁场作用下器件的电流也同时变大,对此认为是器件中的三重态激子与自由载流子的相互作用减弱,引起自由载流子的散射概率变小,迁移率变大的结果.

Electrofluorescent organic light-emitting device with the structure of ITO/NPB/Alq_3/LiF/Al and electrophosphorescent device with the structure of ITO/NPB/CBP：Ir（ppy）_3/BCP/Alq_3/LiF/Al were fabricated.Their electroluminescence properties were measured under an external magnetic field of 50 mT.Compared to the case of without magnetic field,the electroluminescent（EL）efficiencies of the above-mentioned two kinds of devices increase 4.4% and 7%,respectively.Based on the luminescence mechanism of organic light-emitting diodes （OLEDs）, the observed phenomena were explained. The origin of the improvement can be attributed to the Zeeman split of triplet state due to the external magnetic field influence, resulting in the conversion of triplets T＋ into singlet S in the electrofluorescent device and an increase of the rate constants of triplet energy transfer from host to guest in electrophosphorescent device, respectively. At the same time, the reduced concentrations of triplet decreases the interaction of triplets with free carriers, resulting in an increase in the mobility of free carriers within the device and hence increasing the current.