Optical measurements on ZnS nanoclusters have been carried out to investigate surface effects along with quantum size effects. ZnS nanocrystals have been synthesized in the range of 1.5–2.5 nm, using different chemical methods as well as electronic passivating procedures. The size of nanoparticles has been estimated from empirical pseudopotential calculations. We have obtained a significantly narrower size distribution of ZnS nanocrystals than reported in earlier published results. We observed band gap luminescence in mercaptoethanol capped ZnS nanocrystals. Effects of various defect levels on the luminescent behavior of ZnS nanoparticles have been examined

The size dependence of electron energy levels of ZnSe quantum dots were studied by size selective photoluminescence excitation spectroscopy at low temperature. ZnSe quantum dots of different sizes were synthesized by a high temperature wet chemical route. Cubic zinc-blende crystallites with sizes ranging from 1.5to4.5nm showing only band edge luminescence were obtained. Four excited state transitions have been observed in photoluminescence excitation spectroscopy. This study establishes a connection between the electron energy levels of ZnSe quantum dots and their corresponding size. The experimentally observed excited states for ZnSe quantum dots have been analyzed on the basis of “effective mass approximation” calculations. The observed transitions for wide band gap ZnSe are compared with the well studied material, viz., CdSe. The present work enables one to gain further insight into the size dependence of the electronic structure of semiconductor quantum dots.

ZnSe quantum dots have been synthesized using a simple aqueous route. Coating ZnSe quantum dots with a ZnS monolayer, yields a remarkable enhancement in the PL quantum efficiency at room temperature without affecting the spectral distribution. The results suggest that passivation of surface states, along with an increased localization of the hole in core ZnSe layer, gives rise to high luminescence quantum yield.

Articles you may be interested inLinear and nonlinear optical properties of ZnO/ZnS and ZnS/ZnO core shell quantum dots: Effects of shell thickness, impurity, and dielectric environment ZnS quantum dots are synthesized by a high-temperature chemical route with narrow size distribution at diameters of 1.4 and 1.8 nm. Significantly small size dispersion of 1.4-nm-sized ZnS quantum dots is vivid from the transmission electron microscopic measurements. The nonlinear absorption is measured at wavelengths 532 and 520 nm using a picosecond laser in an open aperture z-scan setup. The measured two-photon absorption coefficients are 0.08 and 0.2 cm/GW for smaller and larger nanoparticles. Two photon absorption cross sections for nanoparticles are about six orders of magnitude larger than bulk ZnS.

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