1. Department of Physics, University of Science and Technology of China, 96 Jinzhai Road, Hefei 230026, Anhui. People's Republic of China
2. Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong S.A.R., People's Republic of China
3. Lebedev Physical Institute, Leninsky Prospect 53, Moscow 119991. Russia
4. Kurnakov Institute of General and Inorganic Chemistry, Moscow 117907, Russia