1. Department of Physics and CICECO - Aveiro Institute of Materials; University of Aveiro; 3810-193 Aveiro Portugal
2. Department of Physics; CICECO - Aveiro Institute of Materials and Instituto de Telecomunicações; University of Aveiro; 3810-193 Aveiro Portugal
3. UNESP - Institute of Chemistry; São Paulo State University; P.O. Box 355 14801-970 Araraquara-SP Brazil
4. Department of Electric and Computer Engineering and Instituto de Telecomunicações; Instituto Superior Técnico; Universidade de Lisboa; 1049-001 Lisboa Portugal