1. Key Laboratory for Micro-/Nano-Optoelectronic Devices of the Ministry of Education; School of Physics and Electronics; Hunan University; Changsha 410082 P. R. China
2. Key Laboratory for Colloid and Interface Chemistry of State Education Ministry; School of Chemistry and chemical Engineering; Shandong University; Jinan 250100 P. R. China
3. Tianjin Key Laboratory of Composite and Functional Materials; School of Material Science and Engineering; Tianjin University; Tianjin 300072 P. R. China
4. Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education); Nankai University; Tianjin 300071 P. R. China