1. Jiangsu Key Laboratory for Nanotechnology, Collaborative Innovation Center of Advanced Microstructures, Nanjing National Laboratory of Microstructures, Department of Physics, Nanjing University, Nanjing 210093, P. R. China
2. Fujian Provincial Key Laboratory of Functional Marine Sensing Materials, College of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, P. R. China