Photodynamics of White Luminescence in Organic Thin Films

本研究以DCM、Alq和PBD（或PPCP）组成的有机薄膜为研究对象，分别研究了其红光、绿色和蓝光的白色发光动力学。研究结果如下：1. PBD、Alq和DCM的HOMO-LUMO能级具有I型能量序列，而PPCP和Alq的HOMO-LUMO能级具有II型能量序列.研究了PPCP/Alq双层电致发光器件的白色发光机理，提出了一种利用DCM红光发光的新型器件结构.共掺杂有Alq和DCM的PBD层根据组成表现出白色发光。白色发光的机理是PBD向Alq和DCM以及Alq向DCM的能量转移。得到了上述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光致发光。结果表明，对于更纯的白色发光，DCM的发光是由Alq的能量转移得到的. DCM的发光归因于Alq的弛豫时间常数较短，而PBD的弛豫时间常数较长。没有显着的能量转移已被确认从PBD到Alq。当PBD和Alq同时被激发时，分子分别产生蓝光和绿色光，然后能量转移到DCM上，产生红光。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.