Photoluminescence from Excited Energy Bands in Au25 Nanoclusters

The photoluminescence of Au-25 nanoclusters was studied to elucidate its mechanism. We observed luminescence from the excited band at 2.8 eV in addition to the well-known 1.8 eV emission. The excited band luminescence showed rapid decay described by a stretched exponential function with the mean relaxation time of 2.2 ns. The 1.8 eV luminescence indicated double exponential function decay with the relaxation times of 1.9 and 0.7 mu s. We compared the results with a model and found that the 1.8 eV emission corresponds to the transition between quantum levels of 6sp electronic states, while the excited band luminescence corresponds to that between the 6sp and 5d states. (C) 2011 The Japan Society of Applied Physics