Photodynamics of White Luminescence in Organic Thin Films

研究了由DCM、AlQ和PBD(或PPCP)组成的有机薄膜的白光发光的光动力学特性。研究结果如下：1.PBD、ALQ和DCM的HOMO-LUMO水平具有I型能量序列，而PPCP和ALQ的HOMO-LUMO水平具有II型能量序列。研究了PPCP/AlQ双层电致发光器件的白光发光机理，提出了一种基于DCM红光发光的新型器件结构。与AlQ和DCM共掺杂的PBD层根据组成的不同而表现出白色发光。白光发光的机制是从PBD到ALQ和DCM，也从ALQ到DCM的能量转移。得到了上述部分能量转移的时间常数。测量了入射激光对PBD或AlQ吸收的共振激发下的时间分辨发光。结果表明，对于较纯净的白色发光，利用AlQ的能量转移得到的DCM发光是理想的。DCM的发光可以归因于短时间常数的ALQ和较长时间常数的PBD的弛豫。没有发现从PBD到ALQ的显著能量转移。当PBD和ALQ都被激发时，分子分别产生蓝色和绿色发光，然后能量转移到DCM导致红色发光。DCM不能被光照射有效地激发。

This research was carried out to investigate the photodynamics for white luminescence in organic thin films composed of DCM, Alq, and PBD (or PPCP), which exhibit red, green, and blue luminescence, respectively. The results are summarized as follows;1. HOMO-LUMO levels of PBD, Alq, and DCM possess type-I energy lineup, while those of PPCP and Alq type-II lineup.2. Mechanism of white luminescence in PPCP/Alq double layer EL device was investigated, and a new device structure utilizing red photoluminescence (PL) of DCM is proposed.3. PBD layers codoped with Alq and DCM exhibit white luminescence depending on the composition. The mechanism of white luminescence has been found to be energy transfer from PBD to Alq and to DCM, and also from Alq to DCM. Time constants for some of the above energy transfer were obtained.4. Time-resolved PL was measured under the resonant excitation of the incident laser to the absorption of PBD or Alq. The result shows that for the more pure white luminescence the luminescence of DCM derived by the energy transfer from Alq is desirable.5. Luminescence from DCM has been attributed to the relaxation from Alq with short time constant and from PBD at longer time constant.6. No remarkable energy transfer has been recognized from PBD to Alq. When bothe PBD and Alq are excited, the molecule contribute to blue and green luminescence, respectively, and then the energy transfer to DCM results in red luminescence. DCM cannot be efficiently excited by photo irradiation.