1. Research Institute for Technical Physics and Materials Science, H-1525, P.O. Box 49, Budapest, Hungary
2. Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Béla sqr. 1, H-6720 Szeged, Hungary
3. Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, H-1525, P.O. Box 49, Budapest, Hungary