This work presents experimental observation of the quantized growth of CdTe quantum dots (QD) in the presence of hexadecylamine (HDA), hexylphosphonic acid (HPA), and trioctylphosphine oxide (TOPO) above 200 °C. The crystal growth of CdTe QDs is monitored by in situ UV-vis absorption spectroscopy. The high-temperature absorption spectra indicate the evolution of multiple peaks corresponding to various sizes of QDs. Analysis of the growth kinetics suggests quantized growth of the CdTe QDs in the coordinating solvent mixture. The high-resolution transmission electron microscopy (HRTEM) images and electron diffraction pattern show that most of the QDs have the zinc blende crystal structure. The HRTEM images indicate nanotwinning and stacking faults in larger CdTe QDs. Domain sizes in the HRTEM images correlate well with the smallest observed magic-sized CdTe QDs, in agreement with the proposed aggregation growth mechanism under the experimental conditions. The smallest observed zinc blende CdTe QDs with the diameter of 1.9 ( 0.3 nm are isolated by quenching the reaction mixture during the initial phase of the QD synthesis. The experimental observation suggests that the surprising stability of the magic-sized CdTe QDs is the result of the surface stabilization of the QDs of the HDA and/or HPA. As previously suggested, the aggregation is driven by dipole-dipole interaction between CdTe nanoparticles. The results show that the aggregation of quantum dots could be very important at the early stage of the growth. The magic-sized QDs can be dissolved in either methanol or toluene, which suggests heterogeneity of their surface chemistry. The QDs dissolved in the methanol phase exhibit relatively strong white light emission from 400 to 650 nm with an emission quantum yield of approximately 4%. The QDs dissolved in the toluene phase exhibit very weak emission.

We report a novel method for the synthesis of stable, OH free zinc oxide quantum dots, using an electrochemical route. The optical properties of these quantum dots were studied at room temperature, by taking the optical absorption and luminescence spectra. The band gap luminescence is predominant in ZnO quantum dots synthesized by the present technique, while the green defect induced luminescence, typical of ZnO, is strongly quenched. The role of defects in photoluminescence emission is discussed.

Nanoparticles of indium oxide, a transparent conducting oxide with a band gap close to GaN, were synthesized by pulsed laser ablation of a pure indium metal target. X-ray diffraction and transmission electron microscopy confirmed that nanocrystalline indium oxide particles with a mean diameter of 6.6 nm with a cubic crystal structure were formed. Photoluminescence spectroscopy shows a strong emission peak at 3.78 eV with a weak size dependence.

We compare the spectroscopy of two different morphologies of CdTe/CdSe type-II nanocrystals. Core/ tetrapod and spherical core/shell particles are grown from identical CdTe cores, and both morphologies exhibit type-II spectroscopic behavior. The two morphologies show very different oscillator strengths for the lowest (luminescent) transition; the core/tetrapod particles exhibit larger oscillator strengths for the same amount of spectral shift. A model is presented that explains this difference and accurately predicts emission wavelengths and relative oscillator strengths for the spherical particles. This model uses an elastic continuum treatment to consider strain induced by lattice mismatch at the core/shell interface. The CdTe−CdSe lattice mismatch results in a calculated core pressure of about 2.9 GPa for the particles with the thickest shells. This pressure causes a change in the CdTe conduction band energy of about 0.24 eV and a change in the CdTe lattice parameter of 2.3%. The change in the lattice parameter is also seen in XRD spectra and HRTEM lattice fringe images. Because of the different morphology, core compression is essentially absent in the core/tetrapod particles. The model also considers radial interdiffusion of the selenium and tellurium. Particle annealing results in an alloyed region at the core−shell interface, and the radial composition profile can be calculated from a diffusion treatment. Partial alloying causes the luminescence to shift further to the red, which may be quantitatively understood in terms of calculated radial composition profiles and the known optical band-bowing parameters of CdTe−CdSe alloys.

Twenty feline vaccine-associated sarcomas were examined by transmission electron microscopy. Tumors contained pleomorphic spindle cells, histiocytoid cells, and giant cells. Most tumors contained myofibroblasts, which had morphologic features similar to those of fibroblasts. These cells were further distinguished by subplasmalemmal dense plaques and thin cytoplasmic actin myofilaments organized as elongated bundles concentrated at irregular intervals forming characteristic dense bodies. Intracellular crystalline particulate material was found in 5 of the 20 tumors. Energy dispersive X-ray spectroscopy was used to identify the crystalline material within one tumor as aluminum-based. One tumor from a feline leukemia virus-infected cat contained budding and immature retroviral particles.

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CdSe/CdS and CdSe/ZnS core/shell nanorods have been synthesized with various shell thicknesses and characterized by TEM. The CdSe cores have an aspect ratio of 5.0 ( 0.7. The TEM results show that there are different axial and radial shell growth rates. Shell deposition maintains the rod morphology, with a final aspect ratio of 4.1. The presence of the CdS or ZnS shell greatly affects the particle nonradiative relaxation dynamics and hence the luminescence quantum yields. Both types of shells passivate the surface, reducing the extent of both static and dynamic quenching. Two types of hole acceptors, phenothiazine and hexadecane thiol, have been adsorbed onto these core/shell nanorods, and the effects on the luminescence dynamics are studied using static and time-resolved spectroscopy. ZnS-and CdS-coated particles with adsorbed hole acceptors show differing extents of static and dynamic quenching. These differences may be understood in terms of the different shell morphologies, valence band offsets, and the differences in the phenothiazine and thiol energetics. The extents of static and dynamic quenching are also studied as a function of the phenothiazine or thiol concentration. In both the ZnS-and CdS-coated particles, these concentration dependencies indicate that static quenching is associated with strongly binding sites, presumably where the quencher is bound at a defect in the shell. Dynamic quenching is associated with more weakly binding sites on the surface of the particle.

We observed the quantum-confined band edge emission from ZnSe quantum dots and the size dependence of the energy states, spin-orbit interaction, and Stokes shift. The band edge emission occurs in the ultraviolet blue. The energy gap=Eg+C/dn where d is the diameter and n is 1.19±0.13 and 1.21±0.13 for the first and second electron-hole transitions, respectively. The separation between these transitions approaches the bulk spin-orbit splitting, while the Stokes shift decreases with particle size. Effective mass theories cannot explain these results. Trap emission is observed in some samples in the green and red, resulting from Se-related traps.