1. School of Optoelectronic Engineering & CQUPT-BUL Innovation Institute Chongqing University of Posts and Telecommunications Chongqing 400065 P. R. China
2. Institute of Physics University of Tartu W. Ostwald Str. 1 Tartu 50411 Estonia
3. Faculty of Science and Technology Jan Długosz University 42200 Częstochowa Poland
4. Academy of Romanian Scientists Ilfov Str. No. 3 050044 Bucharest Romania
5. Inorganic Chemistry Department Uzhhorod National University Pidhirna str. 46 88000 Uzhhorod Ukraine
6. West University of Timisoara Bd. V. Parvan 4 300223 Timisoara Romania