1. Chemical Physics and NanoLund, Lund University, P.O. Box 124, SE-22100 Lund, Sweden
2. Department of Materials Science and Engineering, Ocean University of China, Qingdao 266100, China
3. Department of Physics, Chemistry and Biology (IFM), Linköping University, S-581 83 Linköping, Sweden
4. Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
5. Department of Physics, Karlstad University, SE-65188 Karlstad, Sweden