1. Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom
2. Physics Department, M.V. Lomonosov Moscow State University, Moscow, Russia
3. Department of Organic Chemistry, Center for Physical Sciences and Technology, A. Goštauto str. 9, LT-01108 Vilnius, Lithuania
4. A.F. Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
5. Institute of Photonics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland