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

Figure 27 Transmission electron micrograph of Cd 0.88 Mn 0.12 S rods, 7 nm widewith an aspect ratio of f4. (From Ref. 42, reprinted with permission.)anneal treatments above 120jC [75]. Finally, low-temperature inverse-micellereactions appear to benefit from an ‘‘aging’’ process. The micelle solutions areallowed to ‘‘age’’ prior to ligand stabilization and workup. This process isthought to entail particle growth by Ostwald ripening and concurrent loss ofdopant leading to 40–60% less Mn 2+ [69] or Co 2+ [74] in CdS particles. Theresultant DMS NQDs, however, are of superior quality compared to unagedparticles. For example, electronic absorption spectroscopy has been used todemonstrate a change in local environment for Co 2+ in CdS NQDs dissolvedin pyridine (a coordinating solvent) for unaged and aged samples. Unagedsamples are dominated by surface-bound Co 2+ , (Co(A 4 -S) 2 (N(py)) 2 andCo(A 4 -S) 3 (N(py)) 1 , where (A 4 -S) refers to ‘‘lattice sulfides’’ and N(py) topyridine coordination), and entirely lattice-bound Co 2+ [Co(A 4 -S) 4 ] prevailsin aged samples [74]. Interestingly, the aging process, which requires up toseveral days, can be substituted by an isocrystalline shell-growth process thatCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.