1 State Key Lab. on Integrated Optoelectron., Jilin University Region, Changchun 130023, CHN
2 Dept. of Chemistry, Northeast Normal University, Changchun 130024, CHN
3 Dept. of Chemistry, Jilin University, Changchun 130023, CHN
4 Institute of Material Physics, Tianjin Institute of Technology, Tianjin 300191, CHN
5 Material Research Center, Northwestern University, Evanston, IL60208-3108, USA