1. Hanoi University of Mining and Geology, Duc Thang, Tu Liem, Hanoi, Vietnam
2. VNU University of Science, Vietnam National University, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam
3. Quang Tri Teacher Training College, Đông Hà, Quang Tri, Vietnam
4. Department of Physics, Faculty of Basic–Fundamental Sciences, Vietnam Maritime University, 484 Lach Tray, Le Chan, Haiphong, Vietnam
5. Hong Duc University, 565 Quang Trung, Dong Ve, Thanh Hoa, Vietnam
6. Duy Tan University, 03 Quang Trung, Danang, Vietnam