1. Faculty of Physics, Hanoi National University of Education, 136 Xuan thuy, Cau giay, HaNoi, Vietnam
2. Thainguyen University of Education, 28 Luong Ngoc Quyen, Thainguyen 250000, Vietnam
3. Department of Chemistry, Biochemistry and Physics, University of Quebec at Trois-Rivieres, Trois-Rivières G8Z 4M3 Canada