1. Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China, Fax: (internat.) + 852/25472933 or 28571586
2. PKU‐HKU Joint Laboratory on Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, P. R. China
3. Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R. China