1. School of Physics and Opto-Electronic Technology, Collaborative Innovation Center of Rare-Earth Optical Functional Materials and Devices Development, Baoji University of Arts and Sciences, Baoji 721016, Shaanxi, P. R. China
2. College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P. R. China
3. Pillar of Engineering Product Development, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore