1. School of Resources and Chemical Engineering, Sanming University, Sanming 365004, P. R. China
2. Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh 15282, Pennsylvania, United States
3. Centro de Estudios de Semiconductores, Departamento de Física, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela
4. Centro Nacional de Tecnologías Ópticas (CNTO), Mérida 5101, Venezeula
5. Department of Physics, Sogang University, Seoul 04017, South Korea