Study of amplified spontaneous emission and stimulated emission properties of molecularly doped polymer thin films

随着有机／聚合物电致发光材料在有机发光二极管上的应用以及有机晶体管和有机太阳能电池的研制成功，有机／聚合物电致发光材料的优异的光电性能、低廉的生产成本、简单的加工工艺、宽广的选材范围和良好的机械性能等优点极大地吸引科学家们的研究兴趣，并开始了有机／聚合物发光薄膜的放大的自发发射和受激发射行为的研究。有机分子和聚合物的诸多如易得、廉价、结构多样、功能易调节、大的横截面积、高的荧光量子效率和低的自吸收等优点使其制成的激光器在未来光纤通讯领域中呈现了诱人的应用前景。新的有机激光材料不断涌现、器件结构不断推陈出新、新的激发原理不断提出并得到修正已经成为有机／聚合物固体激光研究领域的三大特点。本论文以研究有机材料的激光特性为目的，通过对有机染料DCJTB和三芳胺取代1，8-蔡酰亚胺齐聚物掺杂聚合物薄膜的放大的自发发射和受激发射特性的研究，探讨实现低闭值、高增益光泵浦有机聚合物激光的方法及影响器件性能的因素，阐明放大自发发射的工作机制，为进一步探讨电泵浦有机聚合物激光器提供材料体系和理论依据。1、研究了DCJTB掺杂聚合物薄膜的放大自发发射特性，分析了光泵浦条件下光谱窄化的放大自发发射机制，对ASE增益和损耗进行了讨论和数值拟合，并对增益方程进行了饱和修正。DCJTB：PS薄膜具有较低的闺值（0．16mJ·Pulse~(_1)·cm-2）、高的增益系数（40．72cm-1）、低的损耗值2．49cm一l和高的荧光量子效率（70．4％），其波导增益的波长分布呈明显的洛仑兹分布，增益饱和是均匀展宽的。与DCM比较发现，自由体积是决定材料性能的重要因素，大的自由体积有利于实现低闭值、高增益。我们的研究结果表明，DCJTB是非常好的激光介质材料。2、从ASE的发射波长、ASE闭值、增益和损耗四个技术指标出发，详细研究了激发光波长、聚合物基体、旋涂速度及基片等对DCJTB：PS薄膜放大自发发射（ASE）的影响，短的激发波长和合适的基体材料可以显著地降低闭值和提高增益，薄膜厚度和基片也对ASE性能有很大影响。利用琢lord镜面体系，研究了DCJTB染料掺杂相列向液晶体系的分布反馈激光特性，在电场作用下，可以有效地对TE、TM两种模式的输出强度进行调解。3、把电子传输／发光有机小分子材料Alq3掺杂到DCJTB和C545T掺杂聚合物薄膜，研究了它们的放大自发发射特性。通过在不同激发光波长激发下不同Alq3掺杂浓度对ASE性能影响的研究，发现掺杂Alq3显著地降低了闭值，增加了增益和减小了损耗。由于Alq3是一种良好的半导体有机发光材料，Alq3的引入对电泵浦有机聚合物激光器的研究具有重要的意义。4、研究了三种在4位氨基位置引入不同三芳胺功能基团的红光1，8-蔡酞亚胺齐聚物的放大自发发射特性，研究结果表明，三芳胺取代1，8蔡酞亚胺齐聚物具有低阂值、高增益和低损耗的特点，显示了较小的浓度淬灭效应，即使掺杂浓度高到60％仍可以观察到放大的自发发射现象，表明三芳胺取代1，8茶酞亚胺是一类非常有应用前景的有机半导体激光材料体系。Motivated by the rapid development of organic light-emitting diodes and their excellent optoelectronic performance, low cost, easily fabricated mechanics, the development of lasers made from disordered organic materials has become the focus of many investigations. Organic solid state lasers (OSSLs) have attractively spread applications ranging from element detection through telecommunications due to their large spectral tuning range, their high stimulated emission and their low threshold, which are still not easily accessible by most commonly used inorganic semiconductor materials. Since the demonstration in 1996 of optically pumped lasing from polymers in the solid state, more efforts have been devoted to synthesizing new materials, to understanding their stimulated emission properties and to developing device structures suitable to electrically pumping. In this thesis, the amplified spontaneous emission (ASE) and stimulated emission behaviors of organic dye DCJTB and 4-triarylamine substituted 1,8-naphthalimide semiconductor oligomer were studied in detail for purpose of a comprehensive investigation of lasing properties based on the organic emitting-light materials. The factors of which affect the threshold and gain in organic medium were investigated. The mechanism of the amplified spontaneous emission was elucidated in order to provide the materials and theory assistance required to understand the optical properties of these materials and how that relates to amplification in thin film waveguides on the way to realize electrically pumped organic lasers. 1. We presented a detailed study of the amplified spontaneous emission and gain characteristics of the dye DCJTB doped polymer thin films. Low stimulated emission threshold (O.16mJ-Pulse-1-cm-2), large net gain(40.72 cm"1) and low loss (2.49 cm"1) from DCJTB doped PS films were achieved compared with DCM. The gain distribution along wavelength was fitted well with Lorentzian function indicating that the gain was homogenously broadened. The improvement of lasing performance in DCJTB:PS films was attributed to the larger free volume of DCJTB caused by the introduction of steric spacer groups in DCJTB molecule. These results indicate that the DCJTB doped polymer films could be promising candidates as the gain medium of optically and electrically pumped organic diodes lasers. 2. The factors of which affect the ASE performances such as emission wavelength, threshold gain and loss were examined from four aspects, i.e. excitation wavelength, polymer matrices, spin-coating speed and substrate. It was found that the short excitation wavelength and optimal substrate can significant reduce the threshold energy and enhance the gain coefficient. At the same time, a photo-induced distributed feedback laser employing the DCJTB-doped NCL as active media was achieved by means of the holographic excitation using Lloyd mirror setup. The TE and TM modes of output signal can be continuously tuned on the basis of the reorientation of NLC molecules under an applied electric field. 3. The amplified spontaneous emission (ASE) characteristics in the electron transport /light emitting molecular Alq3 doped polymer films containing dyes DCJTB and C545T were studied in detail. It was found that the introduction of Alq3 in doping polymer films improved significantly the ASE performance with low threshold, high net gain coefficient and low loss, indicating that the doping systems are promising as gain medium in electrically pumped organic solid state lasers due to the excellent semiconductor properties of Alq3. 4. We investigated amplified spontaneous emission (ASE) of new 4-triarylamine substituted 1,8-naphthalimide semiconductor oligomers doped polymer films. A spectral narrowing red emission was achieved following amplified spontaneous emission (ASE) mechanism, which is seldom reported on the 1,8-naphthalimide derivatives as gain medium. Due to the existence of less concentration quenching effects, the 1,8-naphthalimide doped polymer films show low threshold, large net gain, and low loss even though the doping concentration is up to 60%. Our results indicate that 4-triarylamine substituted 1,8-naphthalimide oligomers are attractive candidates as gain medium to realize red organic semiconductor diode lasers