1. Department of Physics, University of Calabria, Via Ponte Bucci Cubo 33b, 87036 Rende, Italy
2. Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e Microsistemi, Via del Fosso del Cavaliere 100, 00133 Rome, Italy
3. Philips Group Innovation—Intellectual Property and Standards, De Lismortel 31 (building 76), 5612 AR Eindhoven, The Netherlands
4. Philips Lighting Research, High Tech Campus 7, 5656AE Eindhoven, The Netherlands
5. Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628CJ Delft, The Netherlands