1. College of Forestry, Northwest A&F University, Yangling, Shaanxi 712100, China
2. Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin, Heilongjiang, 150025, P. R. China
3. School of Science, Guangdong University of Petrochemical Technology, Maoming, Guangdong 525000, P. R. China