1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bld. 11, 1113 Sofia, Bulgaria
2. Centre for Energy Research, 29-33 Konkoly Thege Street, 1121 Budapest, Hungary
3. Institute of Optical Materials and Technologies “Acad. Jordan Malinowski”, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bld. 109, 1113 Sofia, Bulgaria