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

tion spectra and broad PL spectra. Further, the PL QYs for NQDs that emitat >1 Am have been determined in comparison with Rhodamine 6G, whichhas a PL maximum at f550 nm. Typically, spectral overlap between the NQDemission signal and the reference organic dye is required to ensure reasonableQY values by taking into account the spectral response of the detector.An alternative low-temperature approach that has been applied to avariety of systems, including mercury chalcogenides, is the inverse-micellemethod. In general, the reverse-micelle approach entails preparation of asurfactant–polar solvent–nonpolar solvent microemulsion, where the contentof the spontaneously generated spherical micelles is the polar-solventfraction and that of the external matrix is the nonpolar solvent. The surfactantis commonly dioctyl sulfosuccinate, sodium salt (AOT). Precursorcations and anions are added and enter the polar phase. Precipitation followsand particle size is controlled by the size of the inverse-micelle ‘‘nanoreactors,’’as determined by the water content, W, where W = [H 2 O]/[AOT].For example, in an early preparation, AOT was mixed with water and heptane,forming the microemulsion. Cd 2+ , as Cd(ClO 4 ) 2 6H 2 O, was stirred intothe microemulsion, allowing it to become incorporated into the interior ofthe reverse micelles. The selenium precursor was subsequently added and,upon mixing with cadmium, nucleated colloidal CdSe. Untreated solutionswere observed to flocculate within hours, yielding insoluble aggregatednanoparticles. The addition of excess water quickened this process. However,promptly evaporating the solutions to dryness, removing micellarwater, yielded surfactant-encased colloids that could be redissolved in hydrocarbonsolvents. Alternatively, surface passivation could be provided by firstgrowing a cadmium shell via further addition of the Cd 2+ precursor to themicroemulsion, followed by addition of phenyl(trimethylsilyl)selenium(PhSeTMS). PhSe-surface passivation prompted precipitation of the colloidsfrom the microemulsion. The colloids could then be collected by centrifugationor filtering and redissolved in pyridine [27].More recently, the inverse-micelle technique has been applied to mercurychalcogenides as a means to control the fast growth rates characteristicof this system (discussed earlier) [13]. The process employed is similar totraditional micelle approaches; however, the metal and chalcogenide precursorsare phase segregated. The mercury precursor [e.g., mercury(II) acetate]is transferred to the aqueous phase, whereas the sulfur precursor [bis(trimethylsilyl) sulfide, (TMS) 2 S] is introduced to the nonpolar phase. Additionalcontrol over growth rates is provided by the strong mercury ligand,thioglycerol, similar to thiol-stabilized aqueous-based preparations. Growthis arrested by replacing the sulfur solution with aqueous or organometalliccadmium or zinc solutions. The Cd or Zn add to the surface of the growingparticles and sufficiently alter surface reactivity to effectively halt growth.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.