CAREER: Using Photonic Crystals to Control the Emission of Rare Earth-Doped Semiconducting Polymers

用半导体（共轭）聚合物制成的发光二极管（LED）量子效率高达4%，工作寿命为50，000小时。几家公司正在开发使用这些LED的平板显示器。聚合物发光二极管的局限性之一是三重态激子不发光。通过将能量转移到磷光分子和稀土配合物来解决这个问题的初步步骤最近已经采取。本项目的目标之一是优化“掺杂”聚合物薄膜中的能量转移和电荷输运，从而获得高量子效率、低工作电压和高器件稳定性。当前聚合物LED的另一个限制是，大部分发射的光子通过全内反射被捕获在器件中，并且逃逸的光子不能方便地准直成光束或耦合到波导中。该项目的第二个主要目标是使用光子晶体，例如一维介质堆叠和二维光栅，来控制发射的方向性。以前的尝试并没有完全成功，因为不可能使光子晶体的光子带隙足够宽，以完全控制共轭聚合物的发射，共轭聚合物的发射光谱宽度超过100 nm。通过使用稀土掺杂的聚合物，其发射带宽小于4 nm，将有可能使用光子晶体来控制发射的方向性。该项目不仅将提高聚合物基LED的效率和功能，而且将为光子晶体科学和技术的发展提供方便的光源，该项目为学生提供了许多极好的研究机会。他们将与一组化学家合作，设计新的稀土配合物，并学习调节能量转移、电荷转移和光发射的量子力学。他们将与工业界人士互动，学习如何优化聚合物LED。他们将使用计算机建模来设计一维、二维和三维光子晶体，以控制光的发射。他们还将与3M的一个研究团队进行互动，并有机会将聚合物光子晶体科学和技术推向新的方向。大部分研究将由两名研究生完成，但本科生和硕士也有很多机会。此外，学院亦会发展有关纳米科技及有机光电子学的新课程，以供学生作研究用途。纳米技术课程的目的是让几个系的学生意识到在这个令人兴奋的领域的机会，并促进多学科的研究。有机光电子学课程将在PI的实验室中进行几次实验，以便学生可以巩固他们在课堂上所学的内容。高中教师将在夏天参观实验室，并接受培训，使用一套光学设备，以便他们可以向学生演示光子学实验。

Light-emitting diodes (LEDs) made with semiconducting (conjugated) polymersnow have quantum efficiencies as high as 4 % and operating lifetimes of 50,000 hours.Several companies are developing flat panel displays with these LEDs. One of thelimitations of polymer LEDs is that triplet excitons are non-emissive. Initial stepstowards solving this problem by transferring energy to phosphorescent molecules andrare earth complexes have recently been taken. One of the goals of this project is tooptimize energy transfer and charge transport in "doped" polymer films so that highquantum efficiencies, low operating voltages and high device stability can be obtained.Another limitation of current polymer LEDs is that most of the emitted photons aretrapped in the device by total internal reflection and that the photons which do escapecannot conveniently be collimated into a beam or coupled into a waveguide. The secondmajor goal of the project is use photonic crystals, e.g. one-dimensional dielectric stacksand two-dimensional gratings, to control the directionality of emission. Previousattempts to do this have not been fully successful because it was not possible to makephotonic crystals with a photonic band gap wide enough to completely control theemission of conjugated polymers, which have an emission spectrum with a width of morethan 100 nm. By using rare earth-doped polymers, which have emission bandwidths ofless than 4 nm, it will be possible to use photonic crystals to control the directionality ofemission. This project will not only increase the efficiency and functionality of polymer-basedLEDs, but will also provide a convenient light source for developing the scienceand technology of photonic crystals.The project provides many excellent research opportunities for students. Theywill work with a team of chemists to design new rare earth complexes and learn thequantum mechanics that regulate energy transfer, charge transfer and light emission.They will interact with members of industry to learn how to optimize polymer LEDs.They will use computer modeling to design one-, two-, and three-dimensional photoniccrystals to control the emission of light. They will also get to interact with a team ofresearchers at 3M and have the opportunity to push polymer-photonic crystal science andtechnology into new directions. Most of the research will be done by two graduatestudents, but there will be many opportunities for undergraduates and M.S. students totake on short-term projects.New courses on nanotechnology and organic optoelectronics will be developed toprepare students for research. The course on nanotechnology is designed to makestudents in several departments aware of the opportunities in this exciting area and tofoster multidisciplinary research. The course on organic optoelectronics will have severallab sessions in the PI's labs so that students can reinforce what they learn in class. Highschool teachers will visit the labs during the summer and be trained to use a kit of opticalequipment so that they can demonstrate photonics experiments to their students.