Study of multi-wavelength emission organic electroluminescence devices

研究了多色有机电致发光器件的光学特性，为开发高效的有机电致发光显示器件奠定了基础。我们使用以下三种多层OLED进行研究。第一种是OLED，其具有一个发光层，该发光层包含掺杂在主体中的一个客体分子。在10 K下，S_1和T_1态的电子跃迁获得了两种颜色的发射，而在室温下仅获得了一种颜色的发射。为了增强荧光分子的室温T_1发射，主体分子的选择至关重要。第二OLED具有一个发光层，所述发光层包含给出不同发射带的多于两个的客体分子。强度比取决于两个客体分子的浓度比和主体分子的T_1能。第三OLED具有不同颜色发射的两个堆叠的发射层。发射强度比取决于层的厚度和两层的结构。除此之外，我们还研究了在玻璃衬底上蒸镀或旋涂的单层薄膜的吸收、光致发光和椭偏特性。本文主要研究了蓝光FIrpic、绿色Ir（ppy）_3和红光PtOEP荧光粉，以紫外光CBP、聚苯乙烯和聚碳酸酯荧光分子为基质材料。观察到的客体和主体分子的发光强度的温度依赖性。通过量子力学定量分析，阐明了温度依赖性是由于（1）T_1态三个零场分裂子态的自旋-声子弛豫，（2）客体和主体T_1态之间的吸热和放热能量转移，以及（3）客体和主体最低能量T_1态的能量耗散之间的平衡引起的。从OLED获得的量子效率由室温下的这种平衡确定。

Optical characteristics of multi-color organic light emitting diodes (OLEDs) were studied to contribute the development of highly efficient OLD devices for display. We studied using the following three kinds of multi-layer OLEDs. The first one is OLED with one emitting layer containing one guest molecule doped in host. Two color emissions were obtained by electronic transitions from the S_1 and T_1 states at 10 K, but only one color emission was obtained at room temperature. To enhance the T_1 emission at room temperature for fluorescent molecules, selection of host molecule was important. The second OLED has one emitting layer containing more than two guest molecules that give different emission bands. The intensity ratio depends on the concentration ratio of the two guests and on the T_1 energy of host molecule. The third OLED has two stacked emitting layers of different color emission. The emission intensity ratio depends on the thickness of the layers and structure of the two layers. Besides these OLEDs, the absorption, photoluminescence and ellipsometric properties of single layer films evaporated or spin-coated on glass substrate were investigated. Blue-emitting FIrpic, green Ir(ppy)_3 and red PtOEP phosphors were mainly studied, while uv-emitting CBP, polystyrene and polycarbonate fluorescent molecules were used as host materials. Temperature dependence of emission intensity is observed for the guest and host molecules. It is clarified, from quantum-mechanical quantitative analysis, that the temperature dependence is cause by balance among (1)spin-phonon relaxations in three zero-field splitting substates of the T_1 state, (2)endothermic and exothermic energy transfer between the T_1 states of guest and host, and (3)energy dissipation from the lowest-energy T_1 state of either guest or host. The quantum efficiency obtained from OLEDs is determined by such a balance at room temperature.