1. Faculty of Printing, Packaging and Digital Media Technology, Xi’an University of Technology, Xi’an, Shaanxi710048, P. R. China
2. China National Silicon Substrate LED Engineering Technology Research Center, Nanchang University, Nanchang330096, P. R. China
3. School of Chemistry and Chemical Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi710072, P. R. China