1. a Faculty of Chemistry and Chemical Engineering , “Babes-Bolyai” University , 11 Arany Janos, Cluj-Napoca , 3400 , Romania
2. b Faculty of Physics , “Babes-Bolyai” University , 1 M. Kogalniceanu, Cluj-Napoca , 3400 , Romania
3. c Faculty of Science , University of Oradea , 5 Armata Romana, Oradea , 3700 , Romania