1. Luminescent Materials Laboratory, Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy
2. Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, United Kingdom
3. INSTM, UdR Verona, Strada Le Grazie 15, 37134 Verona, Italy
4. Institute of Physics, University of Tartu, W. Ostwald str. 1, 50411 Tartu, Estonia