Photodynamics of White Luminescence in Organic Thin Films

本文研究了DCM、Alq和PBD（或PPCP）组成的有机薄膜（分别发出红、绿、蓝光）的白光动力学特性。结果总结如下：1。PBD、Alq和DCM的HOMO-LUMO水平为i型能量序列，PPCP和Alq的HOMO-LUMO水平为ii型能量序列。研究了PPCP/Alq双层EL器件的白光发光机理，提出了一种利用DCM的红色光致发光（PL）的新器件结构。与Alq和DCM共掺杂的PBD层根据其组成表现出白光。白光的产生机理是PBD向Alq和DCM以及Alq向DCM的能量传递。得到了上述部分能量传递的时间常数。在入射激光对PBD或Alq吸收的共振激发下，测量了时间分辨PL。结果表明，对于更纯的白光，由Alq的能量转移得到的DCM的发光是理想的。DCM的发光归因于Alq的短时间常数弛豫和PBD的长时间常数弛豫。从PBD到Alq没有发现明显的能量转移。当PBD和Alq都被激发时，分子分别发出蓝色和绿色发光，然后能量转移到DCM导致红色发光。光辐照不能有效激发DCM。

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.