Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Figure 7 The size dependence of the resonant Stokes shift. This Stokes shift is thedifference in energy between the pump energy and the peak of the ZPL in the FLNmeasurement. The points labeled X are the experimental values. The solid line is thetheoretical size dependent splitting between the F1 L state and the F2 exciton groundstate (see Fig. 2d).form an exciton–phonon polaron [38] or an exciton–dangling bond magneticpolaron [36].The resonant PL excitation (PLE) studies of CdSe NCs also confirmsthe predicted bright-dark exciton fine structure [39]. The resonant PLEexperiment provides information on both the level splitting and the relativestrength of optical transitions. Although there is a qualitative agreementbetween the experimental data and the theory, the theoretical model clearlyfails to explain saturation of the relative oscillator transition strength in smallNCs (see Fig. 9 in Chap. 2). This discrepancy can be due to the fact that theparabolic band approximation used to describe the conduction and valencebands overestimates the transition oscillator strength is small NCs. Thedetailed description of PLE experiments can be found in Chapter 2.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.