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

Figure 5 (a) Absorption (solid line) and full luminescence (dashed line) spectrafor f2.8-nm-radius CdSe nanocrystals. In luminescence, the sample was excited at2.655 eV (467.0 nm). The downward arrow marks the emission position used in PLE.(b) PLE scan for the same sample. (Adapted from Ref. 9.)plot. The x-axis label, the energy of the first excited state, is a strongly sizedependentparameter. It is also much easier to measure accurately thannanocrystal size. For the y axis, the energy relative to the first excited stateis used. This is chosen, in part, to concentrate on the excited states. However, itis also chosen to eliminate the difficulty in comparing the data with theory.This point aside, Fig. 7 summarizes the size dependence of the first 10transitions for CdSe quantum dots from f1.2 to f5.3 nm in radius. Becausethe exciton Bohr radius is 6 nm in CdSe, these data span the strongconfinement regime in this material.In order to understand this size dependence, one could begin with thesimple particle-in-a-sphere model outlined in Section II.B. The complicatedCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.