1. Key Laboratory of
Luminescence and Optical Information, Ministry of Education, Beijing Jiaotong University, Beijing 100044, People’s Republic of China
2. National Center for Nanoscience and Technology, Beijing 100190, People’s Republic of China
3. Department of Mechanical
and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0656, United States
4. Department
of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States