1. Physics Department, Politecnico di Milano, Piazza Leonardo da Vinci, 20133 Milano, Italy
2. Chemistry, Materials and Chemical Engineering “Giulio Natta” Department, Politecnico di Milano, Via L. Mancinelli 7, 20133 Milano, Italy
3. Department of Science and High Technology, University of Insubria, Via Valleggio 11, 22100 Como, Italy
4. The Courtauld Institute of Art, Department of Conservation and Technology, Somerset House, Strand, London WC2R 0RN, United Kingdom
5. Institute for Photonics and Nanotechnologies, IFN-CNR, Piazza Leonardo da Vinci, 20133 Milano, Italy
6. Institute for Photonics and Nanotechnologies, IFN-CNR, Via Valleggio 11, I-22100 Como, Italy
7. Chemistry, Materials and Chemical Engineering “Giulio Natta” Department, Politecnico di Milano, Piazza Leonardo da Vinci, 20133, Milano, Italy