1. Department of Chemistry; National University of Singapore; Singapore 117543 Singapore
2. State Key Laboratory on Integrated Optoelectronics; College of Electronic Science and Engineering; Jilin University; Changchun 130012 China
3. State Key Laboratory of Rare Earth Resource Utilization; Changchun Institute of Applied Chemistry; Chinese Academy of Sciences; Changchun 130022 China
4. Center for Functional Materials; National University of Singapore Suzhou Research Institute; Suzhou Jiangsu 215123 China