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

amorphous content to the metal flux. The time required for complete phasetransformation was several times that of the simple R-InS to h-InS conversion.VI.NANOCRYSTAL DOPINGIncorporation of dopant ions into the crystal lattice structure of an NQD bydirect substitution of constituent anions or cations involves synthetic challengesunique to the nanosize regime. Doping in nanoparticles entailssynthetic constraints not present when considering doping at the macroscale.The requirements for relatively low growth temperatures (for solvent/ligandcompatibility and controlled growth) and for low posttreatment temperatures(to prevent sintering), as well as the tendency of nanoparticles to efficientlyexclude defects from their cores to their surfaces (see Sect. V) are nanoscalephenomena. Dopant ions in such systems can end up in the external samplematrix, bound to surface ligands, adhered directly to nanoparticle surfaces,doped into near-surface lattice sites, or doped into core lattice sites [64].Given their dominance in the literature thus far, this section will focuson a class of doped materials known, in the bulk phase, as dilute magneticsemiconductors (DMSs). Semiconductors, bulk or nanoparticles, that aredoped with magnetic ions are characterized by a sp–d exchange interactionbetween the host and the dopant, respectively. This interaction providesmagnetic and magneto-optical properties that are unique to the doped material.In the case of doped nanoparticles, the presence of a dopant paramagneticion can essentially mimic the effects of a large external magneticfield. Magneto-optical experiments are, therefore, made possible merely bydoping. For example, fluorescence line-narrowing studies on Mn-doped CdSeNQDs are consistent with previous studies on undoped NQDs in an externalmagnetic field [64]. Further, nanosized DMS materials provide the possibilityfor additional control over material properties as a result of enhanced carrierspatial confinement. Specifically, unusually strong interactions betweenelectron and hole spins and the magnetic ion dopant should exist [65,66].Such carrier spin interactions were observed in Cd(Mn)S [65] and inZn(Mn)Se [66] as giant splitting of electron and hole spin sublevels usingmagnetic circular dichroism (MCD). Under ideal dopant conditions—asingle Mn ion at the center of an NQD—it is predicted that significantlyenhanced spin-level splitting, compared to that in bulk semimagnetic semiconductors,would result [65]. Host–dopant interactions are also apparent insimple PL experiments. Emission from a dopant ion such as Mn 2+ can occurby way of energy transfer from NQD host to dopant and can be highlyefficient (e.g., QY = 22% at 295 K and 75% below 50 K [66]) (Fig. 23). TheCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.