1. Department of Chemistry Southern University of Science and Technology Shenzhen Guangdong 518055 China
2. State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou Guangdong 510641 China
3. Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques South China University of Technology Guangzhou Guangdong 510641 China
4. Materials Research Laboratory and Materials Department University of California Santa Barbara CA 93106 USA
5. Department of Materials Science & Engineering National University of Singapore Singapore 117576 Singapore