1. Optical Materials, CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, Pessac, F‐33608 (France), Fax: (+33) 5 4000 2761
2. Institute for Problems of Material Science, NASc of Ukraine, 3 Krjijanovskogo Str., 03680 Kiev‐142 (Ukraine)