1. Wuhan National Laboratory for Optoelectronics; School of Optical and Electronic Information; Huazhong University of Science and Technology; 1037 Luoyu Road Wuhan 430074 P. R. China
2. Ningbo Institute of Materials Technology & Engineering; Chinese Academy of Sciences; 1219 Zhongguan Road Ningbo 315201 P. R. China
3. Department of Materials Science and Engineering; University of California Los Angeles; 405, Hilgard Avenue Los Angeles CA 90095-9000 USA
4. Department of Materials Science and Engineering; Monash University; Scenic Blvd & Wellington Road Melbourne VIC 3800 Australia