1. Institute of Semiconductors, Guangdong Academy of Sciences, Guangzhou, 510651, P. R. China
2. School of Marine Sciences, Sun Yat-Sen University, Zhuhai, 519082, P. R. China
3. Guangdong Province Key Laboratory of Rare Earth Development and Application, Institute of Rare Metals, Guangdong Academy of Sciences, Guangzhou, 510651, P. R. China