1. Istituto Nanoscienze-CNR, Euromediterranean Center for Nanomaterial Modelling and Technology (ECMT), via Arnesano, I-73100 Lecce, Italy
2. Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, via Arnesano, I-73100 Lecce, Italy
3. The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia 30332, United States
4. Key Laboratory of Green Synthesis and Applications, College of Chemistry, Chongqing Normal University, Chongqing 401331, P. R. China
5. Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China
6. College of Physics and Optoelectronics, South China University of Technology, Guangzhou 510641, P. R. China