1. Department of Materials Science; University of Milano Bicocca; Via Cozzi 55 20125 Milan Italy
2. Department of Earth and Environmental Sciences; University of Milano Bicocca; Piazza Della Scienza 4 20126 Milan Italy
3. Optical Materials Engineering Laboratory; ETH Zürich; 8092 Zürich Switzerland
4. Department of Physics and Astronomy; University of Bologna; Viale Berti-Pichat 6/2 40127 Bologna Italy