1. 1Science Institute, University of Iceland, Dunhagi 3, IS107 Reykjavik, Iceland
2. 2Thin Film Physics, Department of Physics (IFM), Linköping University, SE-581 83 Linköping, Sweden
3. 3Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
4. 4Institut für Angewandte Photophysik, TU Dresden, 01062 Dresden, Germany