1. Guangxi Key Laboratory of Optical and Electronic Materials and Devices, Guangxi Universities Key Laboratory of Non-ferrous Metal Oxide Electronic Functional Materials and Devices, College of Materials Science and Engineering, Guilin University of Technology, Guilin 541004, P. R. China
2. UPR3079 CEMHTI, 1D Avenue de la Recherche Scientifique, 45071 Orléans Cedex2, France
3. Université d’Orléans, Faculté des Sciences, Avenue du Parc Floral, 45067 Orléans Cedex 2, France
4. CEA Saclay, Laboratoire Léon Brillouin, F-91191 Gif Sur Yvette, France