1. State Key Laboratory of Luminescent Materials and Devices Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques Guangdong Engineering Technology Research and Development Centre of Special Optical Fiber Materials and Devices School of Materials Science and Engineering South China University of Technology Guangzhou 510641 China
2. Department of Physics and Engineering Physics University of Saskatchewan 116 Science Place Saskatoon Saskatchewan S7N 5E2 Canada
3. School of Physics and Optoelectronics South China University of Technology Guangzhou Guangdong 510641 China