1. College of Chemistry and Molecular Sciences, Wuhan University, 430072 Wuhan, P. R. China
2. Faculty of Material Science & Chemistry Engineering, China University of Geosciences, Wuhan, Hubei 430074, P. R. China
3. Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China, Fax: +852‐3411‐5862
4. Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
5. Department of Physics, Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China