1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, G. Bonchev, Str., bld. 11, 1113 Sofia, Bulgaria
2. Institute of Optical Materials and Technologies “Acad. Jordan Malinowski”, Bulgarian Academy of Sciences, Blvd. Akad. G. Bonchev 109, 1113 Sofia, Bulgaria
3. Institute of Electronics, Bulgarian Academy of Sciences, Tzarigradsko Shousse 72, 1784 Sofia, Bulgaria