Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (approximately 2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N,N'-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection-related to the highest occupied and lowest unoccupied molecular orbitals-grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.

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Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

Nanoparticles of copper sulfide have been synthesized by reacting a copper ammonia complex with an equimolar thiourea solution in Triton-X 100/cyclohexane water-in-oil microemulsions. The presence of an exceptionally sharp and blue-shifted peak at 475 ± 2 nm in the UV−vis spectrum reveals the formation of quasi-monodispersed, size-quantized particles. Using absorption spectroscopy, the formation of a chalchocite (Cu2S) phase is inferred. The peak position in the absorption spectra was found to be independent of net micellar water content as well as aging effect. It is attributed to the formation of a Cu(I) thiourea complex on the surface of the particles, which are hydrogen bonded to the polyoxyethylene (POE) chain of Triton-X 100 (TX-100). The role of thiourea in the tailoring of particles to the micellar periphery was confirmed by synthesizing the nanoparticles using other S2- agents like H2S, and Na2S. The role of the POE chain in mediating the adsorption was brought out by carrying out the reaction in microemulsions of POE containing surfactants other than TX-100. The kinetics of agglomeration has been studied and fits well in second-order rate law. A further enhancement in the solution stability of the particles was achieved by means of sodium hexametaphosphate.