1. The Open University, Physics and Geology Groups, 16 Klausner St., Tel-Aviv 61392, Israel
2. Enrique Berman Professor of Solar Energy, The Hebrew University, Department of Inorganic and Analytical Chemistry, 91904 Jerusalem, Israel
3. University Claude Bernard Lyon 1, Physico-Chimie des Materiaux Luminescents, CNRS, 69622 Villeurbanne, France
4. Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 937, 50-950 Wrocław, Poland