1. Hebei Provincial Key Laboratory of Optoelectronic Information Materials, and College of Physics Science and Technology; Hebei University; Hebei 071002 Baoding, P. R. China
2. Department of Physics; Blinn College; Bryan TX 77805 USA
3. State Key Laboratory of Metastable Materials Science and Technology; Yanshan University; Hebei 066004 Qinghuangdao, P. R. China