1. Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China, Fax: +852‐3411‐7348
2. Department of Physics and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
3. College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun, 130012, P.R. China