Spectroscopic Studies Pave the Way to Brighter LEDs Volkmar Dierolf, Lehigh University, DMR In 2009, Fuijawara et al. from Osaka University demonstrated a major improvement of the efficiency for red GaN-based LED devices that have an Eu-doped GaN layer as the active region. In order to elucidate the origin of this improvement, Dierolf et al. have performed detailed spectroscopic measurements and showed that the improvement is due to improved crystal quality but energy transfer efficiency of the majority incorporation site for Eu is still low. Dierolf group identified a minority site that has a thousand-fold enhanced energy transfer efficiency. Enriching this Eu-defect species is the key for further (order of magnitude) improvement. Dierolf’s study indicate that the RE-ions-in-GaN technology has potential to achieve wall-plug efficiencies of 10% or higher. Such efficiency values would make the technology viable for applications solid state lighting and display technology. Fig. 2 Fig. 1

Recent breakthroughs in the science of rare earth ions for optical applications have brought the field decisive steps ahead. To further accelerate progress, Dierolf has organized –jointly with several international collaborators– a series of MRS symposia. These symposia which rotate in their location between Europe, US-East Coast, and US-West Coast and bring together 150+ experimentalist and theorists with expertise in semiconductors and insulating materials, specializing in a wide variety applications such as dosimeter, solid state lighting, and displays. These meetings, resulted in a comprehensive proceedings volume (MRS proceedings Vol. 1111) as well as a book in the Springer Series on Topics in Applied Physics (see image) which give excellent overviews of the current state of the art. Bringing the Community Together Volkmar Dierolf, Lehigh University, DMR

Research Opportunity for Undergraduate Students from Underrepresented Groups in Physics Volkmar Dierolf, Lehigh University, DMR Dr. Dierolf’s group has a proud record of hosting undergraduate students from underrepresented groups for 10-week summer research program at Lehigh (10 in the last 5 yrs). Dierolf’s REU student Demitrious Wilson from Washington State University used excitation emission spectroscopy to determine the incorporation of Eu ions into GaN. He determined electron-phonon coupling of the ions. While doing his research opportunity he learned how to operate liquid He cryostats, confocal microscope, and tunable laser and to evaluate complex and vast experimental data sets. At the end of the summer, he gave a talk in the research seminar (see Figs.) and prepared a poster that he will present in upcoming scientific meetings.