1. Solid State Physics Department, National Research Centre, Dokki 12622, Giza, Egypt
2. Molecular and Fluorescence Spectroscopy Lab., Central Laboratories Network, National Research Centre, Dokki 12622, Giza, Egypt
3. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 11, Sofia 1113, Bulgaria
4. Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 11, Sofia 1113, Bulgaria
5. Institute of Electronics, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee, Sofia 1784, Bulgaria