1. Department of Chemistry, Solid State Institute, and the Russell Berrie Nanotechnology Institute, Technion, Haifa 32000, Israel, ElOp Electro Optics Industries Ltd., P.O. Box 1165, Rehovot 76111, Israel, Department of Materials Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel, Laboratoire de Photonique Quantique et Moléculaire, Institut d'Alembert, Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson 94235 Cachan, France