1. Department of Physics, The University of Hong Kong, Hong Kong, China
2. Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
3. Department of Physics, Oslo University, Oslo, Norway
4. State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics, Sun Yat-Sen University, Guangzhou, China
5. Institute of Optoelectronic Material and Technology, South China Normal University, Guangzhou, China