1. Department of Physics, Hainan Normal University, Haikou 571158, P. R. China
2. College of Materials and Metallurgy, Institute of Nanophotonic Physics, Guizhou University, Guiyang 550025, P. R. China
3. State Key Laboratory of Environment Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550003, P. R. China