[1] Shandong Univ, Sch Phys & Microelect, Jinan 250100, Peoples R China
[2] Shandong Univ, State Key Lab Crystal Mat, Jinan 250100, Peoples R China
[3] Shandong Univ, Sch Chem & Chem Engn, Jinan 250100, Peoples R China
[4] Peking Univ, Dept Tech Phys, Beijing 100871, Peoples R China
[5] Peking Univ, Minist Educ China, Key Lab Heavy Ion Phys, Beijing 100871, Peoples R China