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

点击翻译按钮获取中文摘要

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.