1. State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, P. R. China; Department of Chemistry, Shandong University, Jinan 250100, P. R. China; Institute of Optoelectronics, Department of Physics, Shandong University, Jinan 250100, P. R. China; and Semiconductor Institute Region of State Key Laboratory on Integrated Optoelectronics, Chinese Academy of Science, Beijing 100083, P. R. China