1. Research Group “Solid State Lighting”, NanoEnergieTechnikZentrum, University of Duisburg-Essen, Carl-Benz-Str. 199, 47057 Duisburg, Germany
2. Werkstoffe der Elektrotechnik and CENIDE, University of Duisburg-Essen, Bismarckstr. 81, 47057 Duisburg, Germany