1. College of Physics Science and Technology, Shenzhen University, Shenzhen 518060, China
2. Division of Physics and Applied Physics, Centre for Disruptive Photonic Technologies (CDPT), School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
3. Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
4. School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore 639798