1. University of Applied Sciences Muenster, Dep. of Chemical Engineering/Applied Materials Sciences, Stegerwaldstr. 39, 48565 Steinfurt, Germany, Fax: +49‐2551‐962‐187
2. Current address: OSRAM GmbH, Phosphor Development & Applications, Hellabrunner Straße 1, 81543 München
3. School of Chemistry, Box 23, Monash University, Clayton, Vic. 3800, Australia, Fax: +61‐03‐9905‐4597
4. On leave from: Mari Technical State University Yoshkar‐Ola, Institute of Physics, Lenin‐pl. 3, 424000 Yoshkar‐Ola, Russia