1. Department of Physics, Chemistry and Biology; Linköping University; Linköping 58183 Sweden
2. Center for Physical Sciences and Technology; Saulėtekio av. 3 Vilnius LT-10257 Lithuania
3. Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics; Technische Universität Dresden; Dresden 01062 Germany
4. Department of General Physics and Spectroscopy; Faculty of Physics; Vilnius University; Saulėtekio 9 Vilnius LT-10222 Lithuania