1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 11, Acad. G. Bonchev str., 1113 Sofia, Bulgaria
2. Faculty of Chemistry and Pharmacy, Sofia University St. Kliment Ohridski, 1 James Bourchier blvd., 1164 Sofia, Bulgaria
3. Inorganic Solid State Chemistry, Saarland University, Campus Geb. C4 1, 66123 Saarbrücken, Germany
4. Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, 109, Acad. G. Bonchev str., 1113 Sofia, Bulgaria