1. a Institute of Polymers , Bulgarian Academy of Sciences , Acad. G. Bonchev Str., bl. 103-A, 1113, Sofia, Bulgaria
2. b Ecole Polytechnique Fédérale de Lausanne, Laboratory of Lanthanide Supramolecular Chemistry , CH-1015, Lausanne, Switzerland
3. c Department of Ecology , Forestry University of Sofia , 1756, Sofia, Bulgaria
4. d Central Laboratory of Mineralogy and Crystallography , Bulgarian Academy of Sciences , Acad. G. Bonchev Str., bl. 107, 1113, Sofia, Bulgaria