Exciton confinement and stimulated emission from polyfluorene beta-phase; a new direction for polymer lasers.

有机发光器件开发中的一个主要问题是激子（辐射衰减以产生光的分子的激发态）在其寿命期间移动通过器件的容易性。由于有机膜的平均厚度仅为100 nm，激子可以行进相当长的距离，因此它们很有可能发现化学缺陷、其他激子和电荷载流子，并与器件的金属电极碰撞，所有这些都将导致它们被淬灭。因此，为了最大限度地提高这些设备中的光产生效率，找到一种简单的方法来捕获激子而不破坏它们将是有益的，使得最大数量的激子以光的形式放弃能量。在这个项目中，我们将实现这一目标，使用高度有序的聚集体区域内的主机无定形聚合物，以避免任何问题的相分离和设备的不稳定性，在多组分系统。我们最近已经证明，这些所谓的β相在聚辛基芴可以捕获激子和发射强烈，一旦所有的光氧化缺陷已被删除的聚合物。事实上，它们是如此的发射，以至于我们也能够从它们中产生可调谐的放大自发辐射（ASE）。因此，我们将研究限制的影响，β相网站在薄膜和制造设备从薄膜含有β相，研究通过限制提高器件效率。我们将使用飞秒时间分辨光谱来测量限制的强度，并且还测量停止激子迁移如何通过减少各种猝灭机制的影响来增加聚合物的辐射量子效率。由含β相薄膜制成的发光器件将进行优化，以考虑通过聚合物层的电荷迁移率的变化，从而最大限度地发挥限制的积极效益。一名博士生将详细研究薄膜的ASE特性作为β相含量的函数，并制造基于波导的器件来研究器件结构中的ASE。然后我们可以研究外加场和电流对受限激子的影响。从这些测量中，我们将得出使用激子约束和波导结构器件的电泵浦塑料激光器的参数要求。该项目旨在对聚合物发光二极管的设计进行一步改变，并为塑料激光二极管的实现提供指导。

A major problem in the development of organic light emitting devices is the ease by which excitons, the excite states of the molecules which radiatively decay to produce light, move through the device during their lifetime. As the organic films are on average only 100 nm thick, the excitons can travel appreciable distances and so there is a high probability for them to find chemical defects, other excitons and charge carriers and collide with the metal electrodes of the device, all of which will cause them to be quenched. Therefore, to maximise the efficiency of light production in these devices it would be beneficial to find a simple way to trap the excitons without destroying them, so that the maximum number give up there energy as light. In this project we will achieve this using highly ordered aggregate regions within a host amorphous polymer so avoiding any problems with phase segregation and device instability in a multi-component system. We have recently demonstrated that these so called beta-phases in polyoctylfluorene can trap excitons and emit strongly, once all photooxidative defects have been removed from the polymer. In fact they are so emissive that we have also been able to generated tuneable amplified spontaneous emission (ASE) from them. Therefore, we will study the confinement effects of the beta phase sites in films and fabricate devices from films containing beta phase to study improved device efficiency via confinement. We shall characterise the strength of the confinement using femtosecond time resolved spectroscopy and also measure how stopping exciton migration increases the radiative quantum efficiency of the polymer by reducing the effect of various quenching mechanisms. Light emitting devices made from beta phase containing films will be optimised to account for changes in charge mobilities through the polymer layers and so maximise the positive benefits of confinement. A PhD student will make detailed studies of the ASE properties of the films as a function of beta phase content and fabricate waveguide based devices to study ASE in device structures. We can then investigate the effect of applied field and current on the confined excitons. From these measurements we shall derive the parametric requirements for an electrically pumped plastic laser using exciton confinement and waveguide architecture devices. This project aims to make a step change in the design of polymer light emitting diodes and produce guidelines for the realisation of plastic laser diodes.