1. Institute for Solid State Physics and Optics, Wigner Research Centre for Physics; Hungarian Academy of Sciences, Budapest, P.O.B. 49 H-1525 Hungary
2. Institute of Physics, Academy of Sciences of the Czech Republic; Na Slovance 2 Prague 182 21 Czech Republic
3. Department of Organic Chemistry; Institute of Chemical Technology; Technická 5, 166 28 Prague 6 Czech Republic