1. School of Applied Physics and Materials Wuyi University Jiangmen 529000 China
2. School of Physics and Optoelectronics School of Materials Science and Engineering Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied Techniques Guangdong Engineering Technology Research and Development Center of Special Optical Fiber Materials and Devices The State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 China