[1] Graz Tech Univ, Inst Solid State Phys, Christian Doppler Lab Adv Funct Mat, A-8010 Graz, Austria
[2] JOANNEUM RES, Inst Nanostruct Mat & Photon, Christian Doppler Lab Adv Funct Mat, A-8610 Weiz, Austria
[3] Graz Univ Technol, Inst Solid State, A-8610 Graz, Austria
[4] Berg Univ Gesamthsch Wuppertal, D-42097 Wuppertal, Germany
[5] Univ Ulm, D-89069 Ulm, Germany
[6] Univ Florida, Ctr Macromol Sci & Engn, Dept Chem, Gainesville, FL USA