3.2. Apparatus

Fluorescence measurements were performed on a Hitachi Model F-2500 fluorescence spectrophotometer (Hitachi, Tokyo, Japan). The emission spectra were recorded upon excitation at 320 nm. The slits for excitation and emission were both set at 10.0 nm. Steady-state absorption measurements were carried out on a Beckman DU-800 UV-vis spectrophotometer (Beckman Coulter, Inc., Fullerton, CA, USA) by scanning in the range 200–600 nm. Transmission electron microscopy (TEM) images were collected on a Tecnai G2 F20 transmission electron microscope (FEI, Hillsboro, FL, USA) operating at 200 kV.